Savvy growers, instead of reaching for the chemicals, look to a cue from Mother Nature in their search for effective biological products that can prevent and treat certain fungal diseases. The most notable are a specific group of naturally occurring bacteria that can be used to prevent and control fungal infections. These bacteria are called Bacillus subtilis and Bacillus pumilis.

So what are these strange Latin names and, most importantly, how can we use these bacteria to help us grow healthier, happier, and more productive plants? We asked Emily Walter from Agraquest, a provider of biological and low-chemical pest management solutions, to give us the lowdown on our friendly neighborhood fungal disease controllers.

Fungal diseases are a common issue among gardeners. And some of the more common diseases that gardeners struggle to control are powdery mildew and botrytis. Mildew can cause significant damage on some plants. It’s a common, but rarely fatal disease which affects many different types of plants. Most gardeners resort to removing infected plants, but often, the best strategy combines control and treatment.

So What Exactly Is Powdery Mildew?

Powdery mildew is a fungal disease that causes patches of white to gray powder on leaves, stems, fruits or flowers of infected plants. These patches can grow to cover the entire surface on both sides of leaves. Different strains of fungi cause the disease on different plants, but they are all similar in appearance. On some types of plants, the mildew will cause leaves to yellow and prematurely drop, or can cause stunted or deformed plant growth, and eventual plant decline. Mildew thrives in cool, damp conditions with poor air circulation. Indoor and greenhouse growers listen up!

What about Botrytis?

The dreaded botrytis or ‘gray mold’ is a fungal disease that infects many annual and perennial plants. There are several species of the fungus botrytis which can cause significant plant damage; the most common is Botrytis cinerea. Botrytis infections are favored by cool and humid conditions, and are most common during rainy spring and summer weather when temperatures hover around 60°F (15°C). Gray mold can take hold and spread rapidly if your indoor garden sustains long periods of high relative humidity, or outdoors when rainy, drizzly weather continues over several days. Botrytis can affect leaves, stems, crowns, flowers, flower buds, seeds, seedlings, bulbs and just about any other part of a plant with the exception of the roots.

[Left] Scanning Electron Micrograph (SEM) showing a healthy fungal spore on the surface of a leaf. [Rigth] SEM showing a destroyed fungal spore after foliar application of the beneficial bacteria Bacillus subtilis strain QST713. The Bacillus bacteria are the small rod shaped organisms around the top of the picture.

Steps Towards Prevention

Good cultural practices can help prevent and control the spread of fungal issues. The first and most important step toward prevention is to select healthy plants in the first place; these will be more likely to resist fungal attacks.

Plant breeders often select specimens that show resistance to common fungal diseases. This has lead to many different varieties of fruits, flowers and vegetables that have an ever increasing resistance to fungal diseases.

If you have no choice but to use susceptible types of plants outdoors, make sure they are in full sun and will receive a minimum of six hours of sun each day. Isn’t UV radiation great? Indoors, however tempting as it may be, never overcrowd your plants! Allow plenty of fresh air to circulate around your plants, this will discourage disease. When growing indoors, it’s absolutely crucial to focus on maintaining adequate ventilation.

Carefully remove infected fruits, flowers or mildew covered leaves. It is best not to do any removal of diseased plant when they are wet with dew or rain since this could spread fungal spores during conditions which favor infections. Likewise, avoid overhead watering or misting plants especially if fungal disease has been troublesome in the past.

If you encounter a heavily infected leaf, fruit, or flower and are worried about spreading spores around your garden, carefully cover the moldy item with a plastic bag before attempting removal. This way, spores end up in the bag rather than all over your garden!

Always throw away infect plant debris instead of placing it on the compost pile. Spores can overwinter on diseased plant material. New spores can be carried by the wind, so destroying the infected plant parts are essential to help stop the spread of plant disease pathogens.
In an effort to keep fungal diseases at bay, it’s good general practice to keep your indoor garden as clean and tidy as possible. Avoid leaving yellowing or dead leaves hanging from plants, and never keep piles old leaves and trash bags in or near you indoor garden.

Fungal Control Options

There are many chemical controls on the market but they do have some drawbacks. Some controls have temperature and timing restrictions impacting applications or harvest of your crops. Some diseases become resistant to certain chemicals over time as well. If you are using IPM (Integrated Pest Management) in the garden, you will want to preserve beneficial insects, which can be impacted by some chemical controls. Additionally, not all chemical fungicide treatments are acceptable for consumable plants. Some chemicals can only be used when the plant is dormant or cannot be used when the plant is close to harvest time. Carefully read fungicide labels to discover which is right for your particular need.

Beneficial Bacteria – Bacillus as a Fungicide

Another way to control plant diseases is to use products based on beneficial bacterial, specifically Bacillis subtilis or Bacillis pumilis. Both of these bacteria are common found in soil and have been used in horticulture and agriculture for many years.

Bacillus subtilis are naturally-occurring soil borne bacteria, fist characterized in 1835. Over the years varying strains of B. subtilis have been widely used for industrial processes (like detergents or waste water treatments). Bacillus subtilis strains produce extremely photo – and temperature – stable bacterial spores, making them ideal for gardening applications. B. subtilis is also Generally Regarded As Safe (GRAS) by the EPA.

Some strains of Bacillus subtilis are active ingredients in highly effective, broad-spectrum contact fungicides and bactericides. The Bacillus subtilis in these products produce lipopeptides, which are anti-fungal metabolites and anti-bacterial compounds. These lipopeptide compounds that Bacillus subtilis produce kill fungal spores and they are highly stable, resistant to elevated temp and pH extremes.

Lipopeptides are small peptide rings with a lipid (fat) attached. One end of the lipopeptide is negatively charged, the other is “greasy”. A fungal cell membrane can be compared to a sandwich – with hydrophilic (water-loving) surface and a lipophilic (fat-liking) core. The lipopeptides insert into those fungal cell membranes and create small holes in a fungal spore. As, they puncture the cell membrane, cell contents leak out and the fungus is killed.

Some B. subtilis products rely on prolonged wet periods on the leaf surface for the bacteria to become active, produce lipopeptides and then out-compete the fungal spores for leaf surface area. This is not the case with all products – the specific Bacillus subtilis strain QST 713 is unique in that it does not require time to activate, since the bacteria have already done their job producing the lipopeptide metabolites during production. Information about the active ingredient and how it works should be found on the container label of the product you decide to use.

Some Bacillus subtilis strains also illicit plant health and growth promotion in treated plants.  When applied, these strains can trigger the plants’ internal defenses and physiological responses. The effect is systemic – responses are triggered throughout the plant even when a small area is treated.

Products based on Bacillus subtilis are widely used by gardeners and commercial growers since they offer broad spectrum control, have little potential for resistance, have no temperature or time restrictions for application, are non-toxic to beneficial insects (including honey bees) and can be used up to and including the day of harvest. Some products based on B. subtilis are approved for organic production. Since Bacillus subtilis are non-toxic to beneficial insects you can use predatory insects for pest control and beneficial bacteria for disease prevention.

Products based on Bacillus pumilis strains are useful for gardeners for similar reasons. While products based on B. subtilis destroy fungal cell membranes, products based on B. pumilis instead focus on fungal cell walls. The compounds produced by B. pumilis compete with fungal diseases for amino sugars needed to build cell walls, effectively making it impossible for fungal cells to build and grow. B. pumilis does not control bacterial diseases. Instead, it is strongest against rust and mildews. B. pumilis is typically used by a gardener when targeting a specific type of fungal infection that is better controlled by this specific bacteria over the more broad spectrum approach of B. subtilis. Also, B. pumilis strains, like those of B. subtilis, have been shown to trigger plant’s natural defenses.

Both of these beneficial bacteria are best used when applied to plants in a preventative disease control program or at the very first sign of disease. Beneficial bacteria can be used in conjunction with other gardening products. Bacillus subtilis and Bacillus pumilis can be applied every seven days up to the day of harvest if needed. Beneficial bacteria can be applied more often if needed such as every four days during heavy disease pressure. When applying either type of bacteria as a foliar spray one should spay the leaves, shoots and new growth until the plant is dripping wet. Run-off spray will not affect beneficial soil fungi like mycorrhiza. When a gardener is planning to use beneficial bacteria or an organic gardening product to prevent or control fungal and bacterial diseases they should scout the garden often to look for any signs of disease. Strains of these beneficial bacterial can also be found in some compost teas since it can promote plant health and growth promotion.

Practical Tips:

When Do I Use It?

Most Bacillus subtilis or pumilus products can be sprayed as a preventative measure or be used as a curative control. They can be applied early on in the plant’s lifecycle on established cuttings or seedlings, and as late as the day of harvest on mature plants. Most growers freak out at the mere idea of spraying mature flowers or ripe fruit, but these natural Bacillus products are safe for human consumption and actively kill fungal growth.

Spray timing

When using outdoors, it’s best to spray in early morning or late afternoon when light intensity is not too strong. Sunlight contains a natural broad spectrum microbe inhibitor, Ultra Violet light. If applied during strong sunlight, the UV may prevent some Bacillus products from working effectively.
When spraying indoors, it’s also good practice to spray in low light. This may mean raising your grow lights up high before spraying, or spray just before the lights come on or go off.

Spraying the plants

The best fungal control is achieved when the plants are thoroughly wet, and run-off spray is dripping from the leaves. It’s a good idea to use a wetting agent for increased coverage. Avoid adding other foliar additives or nutrients as this may interact negatively with the beneficial bacteria. Spray the underside and top side of the leaves as well as any exposed stems. Sprays can be repeated every 3-4 days if plants are heavily infected, or every 7-10 days as a preventative.

What products contain Bacillus subtilis or pumilus for foliar fungal disease control?

Most good quality compost teas will contain some Bacillus subtilis and pumilus strains, so regular spraying can help with disease prevention. For a more targeted fungal control, the patented Bacillus subtilis strain QST 713 can be found in the commercial product ‘Serenade.’

Other Bacillus subtilis strains are used for root disease control, these include strains GB 03 found in the microbial inoculant ‘Companion’ and strain MBI 600 found pre-mixed into the substrate ‘Pro Mix MX with BioFungicide’.

When growing your favorite fruits, flowers or veggies in your garden, sooner or later you’ll have to deal with thrips feasting on your plants. Usually, the first signs of thrips in your garden will be the visual damage they do to your plants’ leaves. This damage will appear as small, slug like, silvery trails accompanied by patches of white/yellow spots on the leaves. This is the result of thrips piercing the leaf tissue and sucking out the contents of the cells. You may also see accompanying tiny black spots, which are thrips’ droppings. So, not only do they eat your plants but they poop all over them too. Don’t you just love ‘em?

There’s a huge variety of thrips species that feed on cultivated plants, including onion thrips (Thrips tabaci), melon thrips (Thrips palmi) and tobacco thrips (Frankliniella fusca), but worldwide, the most common pests of this species are the western flower thrips (Frankliniella occodentalis). There are subtle differences in color and size among the  species, but seeing as western flower thrips are the most common, we’ll focus on them.

Useless Factoid: You can have many thrips but there is no such thing as a single thrip. Like deer, sheep and pants, the word thrips is used for both singular and plural references.

Thrips - Adult and Larvae

Appearance

Adult western flower thrips are light to dark-brown in color. They are very small, rarely larger than 1.2mm in length, and, when stationary, they look a bit like a tiny splinter of wood. Adult thrips are very evasive and can be difficult to spot. On vegetative plants, they like to spend most of their time on the underside of leaves and will often hide along the edges of the leaf veins. On flowering plants thrips will congregate in the flowers, making them difficult to see. Adult thrips have wings, but they are not great fliers. Although they only fly short trips between leaves or plants, they make many of these short flights a day, which makes them relatively fast at moving around even the largest of crops. Once outdoors and airborne, adult thrips can be caught by winds and easily cover longer distances.

Life Cycle

The rate at which thrips develop and move through their life cycle depends largely on their environment—particularly temperature, humidity and the quality of their food. Adult western flower thrips can live for 30-35 days. During this time the female is capable of laying 2-10 eggs per day, with a total of 150-300 eggs during her lifetime. Rather than the eggs being laid on the surface of a plant, thrips insert their eggs into soft plant tissue, mostly that of leaves, flowers and fruits. One egg at a time is inserted into its own cut in the plant tissue; these eggs are often identified on plants’ leaves as small hard bumps. Eggs take around 4-7 days to hatch at 68-77˚F (20-25˚C). Once hatched they enter their first of two feeding stages as larvae. The larvae are white to orange in color and feed for around 6-10 days at 68-77˚F (20-25˚C) before entering a non-feeding pre-pupa stage, which lasts for 1-2 days. After this fasting, they enter the pupa stage to complete their development into  adulthood. Pupation mostly occurs on the ground or growing media, but it is not uncommon for it to occur on the plant, and it takes around 3-4 days at 68-77˚F (20-25˚C). After pupation they emerge as adults and move quickly up the plant to begin feeding, mating and laying more eggs. The total time from egg to adult is 22-23 days at 68˚F (20˚C) and 14-15 days at 77˚F (25˚C), this shows how integral temperature is to a thrips’ development.

As well as damaging plant tissue through feeding, thrips also harbor and spread viruses, most notably the tomato spotted wilt virus. It is therefore extremely important that once thrips are found within a crop, appropriate action is taken to control them. A very effective way of controlling thrips populations is through the use of biological controls: aka predators. Arguably, one of the most effective control measures for thrips is through the introduction of the predatory mite Amblyseius cucumeris.

Amblyseius cucumeris?

Also called Neoseilus cucumeris, this tiny predatory mite is beige-brown in color and has a pear shaped body less than 1mm long. Cucumeris live on plant foliage and eat a variety of food, mainly small arthropods like thrips larvae. Cucumeris even eat pollen in the absence of prey! Generally, they are not fussy eaters and will also eat spider mite nymphs and eggs, but they offer the best control when introduced to deal with thrips.

Close up of Cucumeris - Image courtesy of Nigel Cattlin/FLPA

Cucumeris is a very small mite and works for you by feeding on the first-instar thrips larvae soon after they have hatched. Adult cucumeris are hungry little warriors and can eat 1-5 thrips larvae per day. Female cucumeris can lay 20-30 eggs at the rate of 1-3 a day, and these are laid mainly on the underside of leaves. After 2-3 days the cucumeris larvae hatch from the egg and develop through two nymphal stages, the protonymph and deutonymph, before they mature as adults. The life cycle takes 11 days at 68˚F (20˚C) and just 8 days at 77˚F (25˚C), which is considerably faster than a thrips’.

As well as temperature, relative humidity (RH) is a very important factor in cucumeris development. Eggs require a RH greater than 60% in order to hatch, and nymphs and adults are happier when the RH is between 65-75%. Growers maintaining an RH lower than 60% can still be successful using cucumeris as thrips control. This is because cucumeris are mostly found on the underside of leaves around the leaf veins, and these areas provide tiny microclimates where humidity is higher. Unlike some predators, cucumeris are able to function in both long and short day-lengths, making them suitable for year round greenhouses and indoor gardens. As long as the relative humidity is adequate and the temperature stays above 50˚F (10˚C), cucumeris will remain active.

Cucumeris are best introduced as a preventative or when thrips numbers are low. As they are generalist predators they can sustain themselves in crops when pest numbers are very low by feeding on pollen. Cucumeris are a great tool for thrips control because they are able to lurk in the shadows when thrips numbers are low and yet devour many thrips larvae when necessary.

As cucumeris can only eat thrips larvae, it’s important to try and maintain high numbers of cucumeris to make sure that the thrips larvae don’t make it to adulthood. By targeting the young developing thrips larvae, cucumeris break the thrips’ life cycle, controlling their population.

Products

You can introduce cucumeris mites into your garden and start the biological control of thrips using two different products and release methods. If you look into purchasing Amblyseius cucumeris from your grow store or a specialist online retailer, you will find they are available in tubes and sachets.

The tubes contain a carrier material, most often a mixture of vermiculite and/or bran, with cucumeris mites throughout the material at all life stages. They are bred in controlled laboratory conditions using other tiny mites as a food source. Packaged and sold in cardboard tubes, the most widely used sizes are the 17 ounce (0.5 liters) tube with 10,000 cucumeris and the 34 ounce (1 liter) tube containing 25,000 or 50,000. Some suppliers offer larger buckets containing 1.3 gallons (5 liters) with 250,000 cucumeris predatory mites!

When introducing cucumeris onto plants from cardboard tubes, a couple of techniques can be employed. For large short plants with a dense canopy, distributing the mites and carrier material over the tops of the plants works best. For taller plants, sprinkling the mites and carrier material over the lower larger leaves is fine. When plants are young and do not have much foliage to catch the carrier material, creating a small heap of material next to the young plants works well as the cucumeris mites can move from this base and walk up the plant’s stem. For an adequate level of thrips control, 50-100 Amblyseius cucumeris should be released per 3.3 square feet (1 square meter); this action should be repeated every 2-4 weeks to keep cucumeris numbers high.

Everest’s Top Tip – When releasing cucumeris from the tube, a gentle rotation while sprinkling will ensure mites in the tube get distributed evenly.

The sachets are made of non-porous paper and are essentially small bags containing a bran material and an active breeding colony of Amblyseius cucumeris. There are a few different sachet deigns; the most popular are the larger sachet with a card hook, and the smaller folding twin sachet. All sachets will have a small hole through which the adult cucumeris can venture out. Hanging the sachets on plant stems or petioles (leaf stems) provides the plant with a continual source of fresh cucumeris ready to eat the thrips. Depending on environment and size, the sachets will release 200-400 cucumeris mites per week and can last for up to six weeks. The sachets provide a protected breeding ground for the cucumeris and enable the colony to thrive in lower humidity. Most sachets available can withstand a constant relative humidity as low as 50% in the growing environment and still work effectively. They should be introduced into the garden at the rate of one sachet per 3.3 square feet (1 square meter), or one per plant. They should be replaced every 4-6 weeks to maintain high cucumeris numbers and continuous plant protection.

Everest’s Top Tip – Sachets should always be positioned in the shade within the crop to prevent direct light drying them out. This will help maintain a long life for the breeding colony.

Tubes vs. Sachets

Tube vs. Sachets

If you have noticed small amounts of thrips damage on your foliage, and want to introduce cucumeris before the thrips become an infestation, it’s best to start by distributing the contents of a tube. This will quickly introduce a healthy population of adult cucumeris to start eating the thrips larvae straight away. A follow-up tube distribution two weeks later, or alternatively the introduction of sachets soon after the first tube release will further support the cucumeris population. Sachets work best as a preventative measure, mainly because it takes time for the cucumeris to establish themselves within the crop. A popular method is to introduce sachets into a newly planted crop or shortly after spraying a compatible pesticide. The spray will knock out a lot of the thrips population and the cucumeris sachets will help maintain the reduced population and prevent outbreaks.

Other Control Measures

Thrips damage on Chrysanthemum leaf - Image courtesy of Nigel Cattlin/FLPA

There are a few other bio-controls that work well in the battle against thrips. Last issue we focused on Hypoaspis miles, which eats soil organisms. Hypoaspis are very useful when used in combination with cucumeris, as they will consume the thrips that complete their life cycle pupating in growing media.

Another popular thrips predator is Orius, the ‘pirate bug.’ This bug preys on all the life stages of thrips, including adults, and can be used in situations where thrips numbers are too high for cucumeris to cope. One last measure you can use for thrips control is Steinerema feltiae, which is a beneficial nematode that attacks thrips pupae in/on the growing media when used as a soil drench, and which also kills adult thrips when used as a foliar spray.

Spraying and Monitoring

Thirps damage on Squash leaf - Image courtesy of Richard Becker/FLPA

When dealing with any pest problem in your indoor garden, it’s important to take the appropriate first step. If you have quite a bad thrips problem with lots of visible damage, you should use an insecticide spray. Introducing any type of predator to deal with a heavy infestation very rarely works. Only after one or two sprays when the pest population is lower should you consider introducing predators. Remember to check the compatibility of your chosen insecticide to make sure it will not kill your introduced predators. Sprays that kill on contact and have a short persistency on plant foliage are most applicable.

To keep an eye on the thrips population in your crop, it’s a good idea to hang blue or yellow sticky cards. These will catch the adult thrips and give you an idea of the size of your infestation. Replacing the sticky traps every 2-4 weeks will give you an even better picture.

In a nut shell:

Amblyseius Cucumeris eat:

1. Preferentially: first-instar thrips larvae.
2. Secondarily: other arthropods such as spider mites and their eggs, and pollen.

They will:

1. Control thrips populations, when introduced early or preventatively.
2. Eat thrips larvae thereby preventing thrips developing into adults.
3. Eat young spider mite nymphs and eggs, but not as a significant control measure.

They won’t:

1. Control large thrips populations.
2. Prevent more damage occurring from existing or invading adults.
3. Work well in temperatures below 50˚F (10˚C) or in low humidity.

Bill Sutherland from Growing Edge Technologies discusses neem oil and how it can form an important part of your indoor garden pest control program.

WHAT IS NEEM OIL?

Neem oil is a natural product derived from the seeds of the neem tree (Azadirachta indica). The neem tree is native to tropical and semi-tropical regions of South Asia but also grows in the Middle East and some parts of Africa. Most of the widespread cultivation and use of neem is in India, where it has been used for over two thousand years as a medicinal treatment for a plethora of ailments and disorders. The neem tree is an evergreen, which grows to around 60 ft (18 m) and produces white aromatic flowers followed by a small fruit that looks much like a large olive. Inside the fruit lies the payload; one large seed from which the oil is extracted by either cold pressing or solvent extraction. A by-product of neem oil extraction is a solid dried product called ‘neem cake’, which can be used as an organic fertilizer as well as a good method of controlling soil-dwelling pests. Here we will focus on the properties, uses and advantages of neem oil when used as a natural pest control agent for your homegrown fruits and flowers.

Please note: Neem oil products are not currently registered for use as a pesticide in Canada.

What does neem oil do?

This may sound disappointing, but it needs to be said: neem is not an insecticide that kills on contact, and it has a low instant ‘knock down’ effect. However, it is still very effective! Unlike other chemical insecticides, neem oil gets into an insect’s body after the ingestion of neem coated plant material and gets to work within a few hours. The predominant active component in neem oil is called azadirachtin, and once in a pest’s body it directly affects the hormonal system, more so than the digestive or nervous system. The way in which azadirachtin targets the hormonal system means that insects are far less likely to develop resistance in future generations. As well as azadirachtin, other liminoid compounds present in natural neem oil (nimbin, salanin, gedunin, azadirone, melandriol and more) play a significant collaborative role in deterring feeding and reducing pest populations.

Biological Effects of Neem Oil on Insects

Historical use and recent research studies show that a broad range of phytophagous (plant eating) pest insects are affected and can be controlled by neem oil, these include:

• Orthoptera: grasshoppers, katydids, crickets etc.
• Coleoptera: wide range of beetles/weevils
• Hemiptera: leafhoppers, aphids, psyllids & some scale insects
• Lepidoptera: cutworms, borers & caterpillars
• Thysanoptera: thrips
• Diptera: Sciarid fly, fruit fly, buffalo/blow & march fly
• Heteroptera: sucking bugs – Green veggie bug, spotted fruit bug etc.
• Others: nematodes, snails, and also some fungi and pathogenic viruses

1. Insect Growth Regulation

Neem oil is unique in nature since it works on juvenile hormones. The insect larva feeds and when it grows, it sheds its old skin and continues growing. This molting phenomenon, also know as ecdysis, is predominantly governed by the enzyme ecdysone. When the ingested neem, or more specifically azadirachtin, enters into the body of larva, the activity of ecdysone is suppressed. This causes molting failure and results in the larva not developing to the next life stage, and ultimately dying. If only a small amount of neem-coated foliage is ingested, and the concentration of azadirachtin is insufficient to cause molting failure, the larva will manage to enter a short-lived prepupal stage where it will die. In some instances, where the concentration of azadirachtin is still less, the adult emerging from the pupa will be malformed and sterile, without any capacity for reproduction.

2. Feeding Deterrent

One of most important properties of neem oil is feeding deterrence. Most insects are permanently hungry during their larval stages, particularly when they are mobile on the leaf surface. An insect’s maxillary gland is responsible for initiating feeding. When these glands give a signal, peristalsis in the alimentary canal is increased, which makes the larva feel hungry, and makes it start eating. When a leaf is treated with neem oil, the presence of the liminoids azadirachtin, salanin and melandriol produces an anti-peristaltic wave in an insect’s alimentary canal, producing something similar to a vomiting sensation combined with a reduced ability to swallow. Because of this sensation, an insect will avoid feeding on neem-treated leaf surfaces.

3. Oviposition Deterrent

Another way in which neem oil reduces pests is by not allowing the females to deposit eggs. This property is known as oviposition deterrence, and quickly thwarts the pest population growth. Interestingly, studies by Knapp & Kashenge (Insect Sci. Applic.2003) on spider mites, and Singh & Singh (Phytoparasitica, 1998) on fruit flies have shown that natural neem oil formulations are more effective as oviposition deterrents and insect mortality than azadirachtin concentrates alone. Results from Knapp’s & Kashenge’s study showed that azadirachtin does not seem to play a major role in the control of spider mites. Although, azadirachtin is an important component of neem oil, the other less studied ingredients seem to have a positive synergistic effect when it comes to effecting the behavior, effectiveness and mortality of plant pests.

Neem Oil’s Effect on Non-Target Species and Beneficial Insects

One of the problems with the use of chemical pesticides has been their impact on non-target species, particularly when used outdoors. Often they have proved harmful to other beneficial species present in the ecosystem. Neem oil products have proved to be remarkably benign to insects such as adult bees and butterflies that pollinate crops and trees, ladybugs that consume aphids, and wasps that act as parasites on various crop pests. As mentioned above, neem oil has to be ingested to be effective. Those insects that feed on plant tissues, therefore, easily succumb. However natural enemies that feed only on other insects, and bees and butterflies that feed on nectar rarely come in contact with significant concentrations of neem oil to cause themselves harm.

Neem Oil’s Other Benefits as a Foliar Spray

Beside its insecticidal and nematicidal properties, neem oil is also a promising agent for the control of viral and fungal plant diseases. Neem oil in combination with paraffin oil has been shown to greatly reduce disease incidences of the yellow vein mosaic virus of okra and legumes, and leaf curl of chili, all of which can cause enormous losses. Neem oil has also been shown to reduce transmission of the tobacco mosaic virus in greenhouse vegetable crops of pepper, cucumber and tomato.

Neem oil has been demonstrated to suppress fungal activity. Fungi are constantly evolving enemies of growers and some can reach epidemic proportions. Neem oil has been shown to protect seeds against fungal diseases while in storage, and be beneficial as a preventative spray for fungal leaf diseases such as powdery and downy mildew.

Neem oil also contains some key nutrients that make it a good foliar fertilizer. A typical good quality neem oil product found in your local grow store will contain the following plant nutrients:

• Total Nitrogen 1.20% by mass
• Phosphorus as P 0.07% by mass
• Potassium as K 0.01% by mass
• Magnesium as Mg 0.03% by mass
• Copper as Cu 10 ppm
• Magnesium, as Mn 0.40 ppm
• Zinc as Zn 20.00 ppm
• Iron content 14.00 ppm

So, not only will regular spraying of neem oil onto your plant foliage control pests, it will also help prevent diseases and act as a foliage fertilizer! Amazing stuff.

How to Use Natural Cold-Pressed Neem Oil:

Foliar Spraying

Like most of the vegetable oils, natural cold-pressed Neem oil is non-soluble in water and has to be made soluble with suitable emulsifiers before spraying. Some commonly available emulsifiers that can be used are liquid soaps, eco-friendly detergents, surfactants, wetting agents, soap nut powder, and many other organic emulsifiers.

1. Collect together your equipment.
2. To make 10 liters of spray-able neem, pour 1 liter of water into a container, add 10–15 ml of liquid soap, or a suitable emulsifier, and agitate well until the soap/emulsifiers completely dissolve.
3. To this solution add 50 ml of neem oil and agitate well until a pale yellowish white emulsion is formed.
4. Add this prepared emulsion to 9 liters of water in a bucket and stir thoroughly. The neem solution is now ready for spraying.

Spraying should be done within 8 hours of mixing, using a suitable sprayer. This solution can be used as a foliar spray on crops, and also can be sprayed on the surface of growing media for effective action against root pests.

It is recommended to repeat the spraying 5 times at intervals of 7 to 10 days. Spraying should be undertaken during periods of low light intensity; outdoors or in greenhouses this should be in the early morning or late in the evening. If you grow under lights, raise them high and consider turning a few off to reduce light intensity before spraying.

Soil Drench

• To make 10 liters of drench-able neem. Add 1 liter of water to a container. Add 20–30 ml of liquid soap, or suitable emulsifier, and agitate well until the soap/emulsifiers completely dissolve.
• To this solution add 250–350 ml of neem oil and agitate well until a pale yellowish white emulsion is formed.
• Add this prepared emulsion to 9 liters of water in a bucket and stir thoroughly. The neem solution is now ready to pour onto the growing medium. Apply enough for a small amount of run-off to occur.

Please Note: Drenching potting soil with neem will adversely affect the beneficial biology of the rhizosphere. If you need to drench the root zone with neem, a follow up application with a good quality actively aerated compost tea will help to re-inoculate the beneficial bacteria, fungi and protozoa.

Neem Oil’s Effect on Plants

Neem oil not only coats the plant foliage after spraying, it is actually absorbed into the leaf material and can be transported around the plant systemically. Neem’s liminoid compounds (mainly azadirachtin) can be taken up by the roots after root zone applications, thereby reaching leaf and stem material throughout the whole plant. This reinforces the anti-feeding deterrent properties or neem oil, which makes the whole plant rather unappealing to invading pests.

Due to this persistence in the plant, neem oil products should not be used on plants that are approaching maturity. As a general rule, avoid spraying or soil drenching neem oil on plants that have five weeks left before harvest. As mentioned above, neem products have been used topically and ingested for medicinal use by humans for thousands of years and are completely non-toxic. However, neem has a very bitter taste that can, if used too late in a plant’s life cycle, be passed into the developing consumable produce.

Summary of the Advantages of Neem Oil

1. Broad spectrum of activity
2. No known insecticide resistance mechanisms
3. Compatible with many other insecticides and fungicides
4. New mode of action with possible multiple sites of attack
5. Low use rates
6. Compatible with other biological control agents for Integrated Pest Management programs.
7. Not persistent in the environment
8. Minimal impact on non-target organisms
9. Formulation flexibility
10. Application flexibility — can be sprayed or drenched

You’ve all heard the old adage, “Your enemy’s enemy is your friend.” Well, it’s never truer than in the world of indoor gardening! Savvy growers have been using “predators” for years. A predator is just another name for a beneficial insect – an insect that feeds on the pests you hate! Usually Mother Nature keeps everything in check. Indoors, you have to take the role of Mother Nature, otherwise a rogue pest can breed uncontrollably and quickly overwhelm your garden. With this in mind, we thought we’d put together a regular feature on predator insects. After all, it’s good to know who your friends are!

Hypoaspis Miles vs. Fungus Gnats

Seeing the first signs of fungus gnats? Allow us to introduce you to a good friend of ours: Hypoaspis miles. These guys are truly fantastic predatory insects all gardeners need to know about. This tiny mite is less than 1mm in size and resides in the top few inches of the growing media preying on a variety of soil organisms, but is especially useful for the control of fungus gnat larvae (aka Sciarid fly larvae).

What are Fungus Gnats?

The most common root pests that lurk in your growing media are without doubt the larvae of fungus gnats. These pesky little insects will usually appear in your garden as harmless looking small 3-5mm black flies. True, the black files themselves won’t actually do any direct damage to your plants, it’s their habitual egg laying that’s the problem. The flies are attracted to wet growing media, particularly organic substrates like potting soils and coco coir or anything with algae growing on it. After mating the female flies can lay anywhere between 50 and 200 eggs which hatch in two to three days. Once hatched the larvae, which look like tiny maggots, develop through four life stages or ‘instars’ over a period of two to three weeks. At the end of this period they normally reach around 5mm in length and are translucent white color with a distinctive black head. You can often see their guts throughout the length of the larvae with their previously eaten food moving through.

The larvae move through the upper surface of the growing media feeding on decaying organic material, algae and fungus but more importantly they eat living plant material, mostly roots but also stem tissue. As a result of this root tissue damage they open the plant up to a variety of disease such a Pythium, Phytophthora and Fusarium. Plants under attack from fungus gnats will often slow down in growth, leaves may discolor, nutrient and water uptake will be affected and in severe cases the plant will wilt and if left untreated it may die.

After two-three weeks of feeding the larvae will enter a pupation stage for three-four days until they emerge as an adult fly. Adult fungus gnat flies can live and lay eggs for between one and three weeks. At temperatures above 77°F (25°C) the complete life cycle from egg to larvae to adult fly takes three to four weeks.

Hypoaspis miles?

Hypoaspis are predators that feed on fungus gnat larvae, springtails, thrips pupae and other small harmful soil insects. When introduced into a growing area that isn’t already plagued by fungus gnats, they have a significant impact in reducing and eventually eradicating them. They don’t work effectively when pest number are high, mainly because they can’t eat everything!

Hypoaspis miles is light brown in color with a darker V-shaped making on its back, this dark V is due to the slightly darker dorsal shield on top of a slightly lighter colored body. They mostly live in the upper surface of growing media. In compacted growing media that may be only the first half inch but in looser more open growing media that may roam down two inches below the surface or more. Hypoaspis prefer growing media high in organic matter such as peat or coco coir but they will happily establish populations in rockwool, perlite and expanded clay pebbles too.

Females lay oval eggs in the growing media at the rate of two to three per day. The eggs hatch in approximately six days (at 68°F (20°C) but this figure is dependent on temperature) into six legged white-beige larvae. After two days they enter the protonymphal stage followed by the deutonymphal stage which actively feed for around ten days before becoming adult. The total development time from egg to adult takes between 17-18 days (again at 68°F (20°C)) when they have plenty of prey to eat. Hypoaspis miles adults can live for between 4- 5 months, and usually have an even population ratio of one female to every one male.

Temperature plays a huge role in the development time for Hypoaspis, at 59°F (15°C) the development time extend to 34 days and at temperature lower than 50°F (10°C) development almost stops. The mites will recover when the temperature rises, as long temperatures no lower than 10°C are sustained for long periods. Temperature below 46°F (8°C) and above 90°F (32°C) are detrimental to their development. At 75°F (24°C), the Hypoaspis development cycle shortens to around 12 days showing just how important temperature is to their reproduction and growth.

Hypoaspis are ferocious eaters of fungus gnat larvae! Hooray! An astonishing eight first instar larvae can be consumed by adult Hypoaspis each day! Contrary to popular belief, Hypoaspis will not eat fungus gnat eat eggs or pupae. They can attack and kill up to one fourth instar larvae per day, but as fungus gnat larvae reach maturity they can get up to seven times larger than Hypoaspis adults making it possible for them to be attacked but not completely consumed. Some uncommonly large fungus gnat larvae may be attacked but not be killed by Hypoaspis due to their size. However, the most import life stage to target is the young developing fungus gnat larvae. When these are removed fewer and fewer make it to the pupae stage which mean a huge reduction in adult flies. This effectively throws a huge spanner in the cogs of the fungus gnat breeding machine, totally disrupting their life cycle, and as the Hypoaspis population grows the fungus gnats get wiped out. Read it and weep fungus gnats!

One key attribute that makes Hypoaspis such a good biological control is their ability to last for up to 70 days without food! In the absence of fungus gnat larvae Hypoaspis can sustain themselves on nematodes, soil microorganisms, algae or in some cases decomposing plant debris, but they do not feed on live plants. This handy generalist feeding approach prevents the population from crashing after eating their way through lots of fungus gnat larvae. Once up to a healthy population size they literally form an army of mites scavenging through the growing media surface constantly in search of prey. This makes Hypoaspis an excellent preventative measure as well as a key tool in the fight against existing fungus gnat populations.

Hypoasis are also know to feed on thrips pupae, which often fall from plants and into the growing media before turning into adults. Hypoaspis are not efficient as a standalone solution to thrips control, but they are effective when used in combination with Amblyseius cucumeris (above ground thrips predator) or spray programs.

Geeky Fact
While they are mostly found below ground during the day, many entomologists have observed Hypoaspis miles climbing up stems and onto foliage low down on plants during humid nights. Here they have been observed feeding on mealybugs, thrips larvae and other organisms.

When purchasing Hypoaspis miles from your grow store, garden center or specialist supplier they most often come in a carrier material of peat and vermiculite. They are bred on this carrier material in controlled laboratory conditions using the tiny storage mite (Tyrophagus putrescentiae) as a food source. This is then packaged and sold in cardboard tubes ranging in size, the most widely used are either 17 ounce (0.5 liters) tubes with 10,000 Hypoaspis or 34 ounce (1 liter) containing 25,000. For larger growers some suppliers offer larger buckets containing a gallon or more with over 100,000 predatory mites in. The peat and vermiculite mix will contain all stages of Hypoaspis including adults, eggs and immature mites.

Left to right, 17 ounce tube, open tube showing peat/vermiculite mix, one low infestation dose

Releasing the mites into your garden is easy. Simply sprinkle the mixture onto the surface of the growing media. Application rates vary depending on the level of infestation. Most biological control companies recommend using 30 mites per square foot of ground area as a preventative measure and up to 120 per square foot for treating existing infestations. If you’re growing in pots, around one level teaspoon at the base of each plant will be enough as a preventative and one heaped teaspoon for existing fungus gnat problems. A 34 ounce container of Hypoaspis miles retails for around $40.00 (USD) and can treat between 100-200 three gallon pots.

If fungus gnats are a constant problem in your indoor garden, you should introduce Hypoaspis predators one to two weeks after planting into the final pot/system. Top up two to three weeks later with a second application to help build up the Hypoaspis population.

Top Tip!
Before distributing the mites into your garden roll the tube back a forth a few times and leave it on its side for ten minutes. This will create a more uniform spread of Hypoaspis mites within the peat-vermiculite mix before dispersal. If stored upright for too long all the mites will try to make their way to the surface of the mix which will lead to the first few applications getting all the goodies.

Hypoaspis are sensitive to some chemical foliar pesticides as run-off can drip onto the surface of growing media. Pyrethrum products and more importantly their synthetic cousin’s permethrin and bifenthrin will have longer term harmful consequences on the growth of Hypoaspis populations and should be avoided. Be sure to check the compatibility of your chosen pesticide with your predators before application.

If you are struggling to control fungus gnats in your garden and you need a quick fix help the Hypoaspis predators get on top of the situation try using a bacterial larvicide containing Bacillus thuringiensis israelensis (Bti). This bacteria kills the active larvae but not Hypoaspis. Another compatible bio-control is the beneficial nematodes Steinernema feltia. These natural microscopic parasites will infect the fungus gnat larvae quickly and effectively without harming the Hypoaspis mites.

Using sticky yellow traps around the canopy and at the base of the plants is also great idea. Not only will these trap the adults and prevent them from laying eggs, but they can be used as monitoring cards to keep an eye on fungus gnat numbers. Simply look at the cards, make a note of the amount of flies trapped and replace the traps each week. A steady decline in fungus gnat numbers should be observed after releasing the predators.

In a nut shell

Hypoaspis miles eat:

1) Preferentially; fungus gnat larvae and thrips pupae

2) Secondarily; other tiny soil organisms algae and plant debris

They will:

1) Control fungus gnat population keeping the pest to a minimum and over time eradicate them

2) Aid in the control of thrips species that pupate in the growing media

Should be used:

1) When fungus gnat numbers are low

2) When growing media temperatures are above 10°C

Should not be used:

1) As a sole treatment for a fungus gnat infestation, they will not be able to cope with the amount of pests.

2) As a sole treatment for thrips.

3) In conjunction with pesticides before checking compatibility. 

Have you ever been given this odd-sounding advice? Even when we are encouraged to try and understand how plants work, our inherent tendency to personify the natural world is inescapable. Growers often like to draw parallels between humans and plants, after all, there’s no doubt that plants are marvelous, highly specialized and well-adapted organisms. You might even go as far to say they are “intelligent.” But let’s be honest here. Plants are totally different from us, especially in the way they react and respond to their environment. However, if we can get our heads around the world from a plant’s perspective, we become what is commonly referred to as “green-fingered.” We become … better growers.

Have you ever wondered how plants “feel” humidity? An understanding of what humidity is, what it means to plants, and how you can manage it in your indoor garden will help you and your plants stay happy all year round.
The humidity of the air is basically the amount of water in the air. Water can only truly stay in the air when it is the invisible gas – water vapor. Small droplets of water in air, such as fog or mist, are not water vapor; they are simply larger particles of water temporarily suspended in the air that are ready to be turned into water vapor by evaporation.

Temperature plays an important role when it comes to humidity. The warmer the air, the more water vapor it can hold. This means the maximum amount of water that air can hold is directly related to the temperature of the air. As the amount of water air can hold constantly changes with temperature it is difficult to pin an absolute or fixed amount of water that can be held by air. So what’s the best way to quantify humidity if the goal posts are changing all the time? The answer is something called Relative Humidity (RH) – this is a measure in terms of percentage, of the water vapor in the air compared to the total amount of water vapor that the air could potentially hold at a given temperature.

Why is RH so important?

As growers we measure the RH of our gardens using digital or analogue hygrometers. These readings are very important because RH has a direct effect on the plant’s ability to transpire and therefore grow. Generally, plants do not like to lose lots of water through transpiration. Plants have some degree of control of their rate of transpiration through management of their stomata but the general rule is the drier the air, the more plants will transpire.
Now let’s move on to the idea of “pressure” – this is an important concept to grasp when it comes to understanding a plant’s response to humidity. All gasses in the air exert a pressure. The more water vapor in the air the greater the vapor pressure. This means that in high RH conditions there is a greater vapor pressure being exerted on plants than in low RH conditions. High vapor pressure can be thought of as a force in the air pushing on the plants from all directions. This pressure is exerted onto the leaves by the high concentration of water vapor in the air making it harder for the plant to ‘push back’ by losing water into the air by transpiration. This is why with high RH plants transpire less. Conversely, in environments with low RH, only a small amount of pressure is exerted on the plants’ leaves, making it easy for them to lose water into the air.

What is Vapor Pressure Deficit (VPD)?

VPD can be defined as the difference (or deficit) between the pressure exerted by water vapor that could be held in saturated air (100% RH) and the pressure exerted by the water vapor that is actually held in the air being measured.
The VPD is currently regarded of how plants really ‘feel’ and react to the humidity in the growing environment. From a plant’s perspective the VPD is the difference between the vapor pressure inside the leaf compared to the vapor pressure of the air. If we look at it with an RH hat on; the water in the leaf and the water and air mixture leaving the stomata is (more often than not) completely saturated -100% RH. If the air outside the leaf is less than 100% RH there is potential for water vapor to enter the air because gasses and liquids like to move from areas of high concentration (in this example the leaf) into areas of lower concentration (the air). So, in terms of growing plants, the VPD can be thought of as the shortage of vapor pressure in the air compared to within the leaf itself.

Another way of thinking about VPD is the atmospheric demand for water or the ‘drying power’ of the air. VPD is usually measured in pressure units, most commonly millibars or kilopascals, and is essentially a combination of temperature and relative humidity in a single value. VPD values run in the opposite way to RH vales, so when RH is high VPD is low. The higher the VPD value, the greater the potential the air has for sucking moisture out of the plant.
As mentioned above, VPD provides a more accurate picture of how plants feel their environment in relation to temperature and humidity which gives us growers a better platform for environmental control. The only problem with VPD is it’s difficult to determine accurately because you need to know the leaf temperature. This is quite a complex issue as leaf temperature can vary from leaf to leaf depending on many factors such as if a leaf is in direct light, partial shade or full shade. The most practical approach that most environmental control companies use to assess VPD is to take measurements of air temperature within the crop canopy. For humidity control purposes it’s not necessary to measure the actual leaf VPD to within strict guidelines, what we want is to gain insight into is how the current temperature and humidity surrounding the crop is affecting the plants. A well positioned sensor measuring the air temperature and humidity close to, or just below, the crop canopy is adequate for providing a good indication of actual leaf conditions.

Managing Humidity

Managing the humidity in your indoor garden is essential to keep plants happy and transpiring at a healthy rate. Transpiration is very important for healthy plant growth because the evaporation of water vapor from the leaf into the air actively cools the leaf tissue. The temperature of a healthy transpiring leaf can be up to 2-6°C lower than a non-transpiring leaf, this may seem like a big temperature difference but to put it into perspective around 90% of a healthy plant’s water uptake is transpired while only around 10% is used for growth. This shows just how important it is to try and control your plants environment to encourage healthy transpiration and therefore healthy growth.
So what should you aim to keep your humidity at? Many growers say a RH of 70% is good for vegetative growth and 50% is good for generative (fruiting /flowering) growth. This advice can be followed with some degree of success but it’s not the whole story as it fails to take into account the air temperature.

Humidification systems to increase RH.

Table 1 shows the VPD in millibars at various air temperatures and relative humidity. Most cultivated plants grow well at VPDs between 8 and 10, so this is the green shaded area. Please note that the ideal VPD range varies for different types of plants and the stage of growth. The blue shaded are on the right indicates humidification is needed where the red shaded area on the left indicates dehumidification is needed.

By looking at this example we can see that at 70% RH the temperate should be between 72-79°F (22-26°C) to maintain healthy VPDs. If your growing environment runs on the warm side during summer, like many indoor growers, a RH of 75% should be maintained for temperatures between 79-84°F (26-29°C.)

The problem with running a high relative humidity when growing indoors it that fungal diseases can become an issue and carbon filters become less effective. It is commonly stated that above 60% RH the absorption efficiency drops and above 85% most carbon filters will stop working altogether. For this reason it is good practice to run your RH between 60-70% with the upper temperature limit depending on your crop’s ideal VPD range, in the example it would be 64-79°F (18-26°C.)

The table also shows that if your temperature is above 72°F (22°C), 50% RH becomes critically low and should generally be avoided to minimize plant stress.
Please understand that by presenting this information we do not want you to go to your indoor gardens and run your growing environment to within strict VPD values. What’s important to take from this is that VPD can help you provide a better indication of how much moisture the air wants to pull from your plants than RH can.
If you want to work out for yourself the VPD of your plants leaves you can follow the steps below:

1. Measure the leaf temperature and look up the vapor pressure at 100% RH on table 2 below.
2. Measure the air temperature and relative humidity and look up the nearest vapor pressure figure on table 2.
3. Subtract the air vapor pressure from the leaf vapor pressure

Example:
Leaf Temperature = 24°C (100% RH)     Leaf VP: 29.8
Air Temperature = 25°C @ 60% RH     Air VP:     19.0
VPD=     10.8

Humidity’s Effect on Plants

Plants cope with changing humidity by adjusting the stomata on the leaves. Stomata open wider as VPD decreases (high RH) and they begin to close as VPD increases (low RH). Stomata begin to close in response to low RH to prevent excessive water loss and eventually wilting but this closure also affects the rate of photosynthesis because CO2 is absorbed through the stomata openings. Consistently low RH will often cause very slow growth or even stunting. Humidity therefore indirectly affects the rate of photosynthesis so at higher humidity levels the stomata are open allowing co2 to be absorbed.

Leaf roll on Thai basil- Localized humidity stress causes by the lights being too close.

When humidity gets too low plants will really struggle to grow. In response to high VPD plants will try to stop the excessive water loss from their leaves by trying to avoid light hitting the surface of the leaf. They do this by rolling the leaf inwards from the margins to form tube like structures in an attempt to expose less of the leaf surface to the light, as shown in the photo.

For most plants, growth tends to be improved at high RH but excessive humidity can also encourage some unfavorable growth attributes. Low VPD causes low transpiration which limits the transport of minerals, particularly calcium as it moves in the transpiration stream of the plant – the xylem.  If VPD is very low (95-100% RH) and the plants are unable to transpire any water into the air, pressure within the plant starts to build up. When this is coupled with a wet root zone, which creates high root pressure, it combines to create excessive pressure within the plant which can lead to water being forced out of leaves at their edges in a process called guttation. Some plants have modified stomata at their leaf edges called hydathodes which are specially adapted to allow guttation to occur. Guttation can be spotted when the edges of leaves have small water droplets on, most evident in early morning or just after the lights have come on. If you see leaves that appear burnt at the edges or have white crystalline circular deposits at the edges it could be evidence that guttation has occurred.

Guttation on tomato plants caused by high RH and wet coco coir.

Powdery Mildew from poor humidity control.

Most growers are well aware that with high humidity comes and increased risk of fungal diseases. Water droplets can form on leaves when water vapor condenses out of the air as temperature drops, providing the perfect breeding ground for diseases like botrytis and powdery mildew. If humidity remains high it further promotes the growth of fungal diseases. The water droplet exuded through guttation also creates the perfect environment for fungal spores to germinate inviting disease to take hold.

Quick reference chart:

So hopefully now you are not just ‘thinking like a plant’ – you’re ‘feeling it’ too!

Next time, part two of Plantworks will be looking at foliar spraying and how plants absorb nutrients into their leaves.

As we’ve learned in part 1 and part 2, in order to grow successfully in a hydroponic system, there are certain basics that always need to be kept in check: otherwise, plant performance inevitably suffers. After covering source water, nutrient and pH, world-renowned hydroponics expert Michael Christan breaks down the final ingredients of a healthy indoor growing environment: oxygen, light, temperature, humidity, air circulation and CO2.

Photos courtesy of AmHydro.

The 5 basics of recirculation and plant performance:

1. Pure source water
2. Balanced nutrient ions/anions (EC)
3. Optimum pH
4. Plentiful oxygen availability
5. Optimum light/temp/humidity/air circulation/CO2

The Importance of Oxygen

It’s obvious that loose, friable soil with organic matter and thriving microbes grows plants much better than tight, clay soil devoid of organic matter. The primary missing ingredient in the latter is air (oxygen) availability.

The air we breathe is composed of gasses: 78% nitrogen (N2), 21% oxygen (02), 0.9% argon (Ar) and 0.03% carbon dioxide (CO2). The one we’re focusing on in this article is oxygen. The action of microbes on organic matter in a loose soil produces air pockets as organic matter is mineralized. These oxygen pockets are crucial to the survival and rapid colonization of healthy microbial populations. When the organic matter in the soil is fully consumed by the microbes and plants have consumed all the minerals, oxygen becomes depleted and, if more organic matter is not reapplied, plant performance slows and pathogenic (anaerobic) microbes can colonize. This condition is best avoided.

In media-based recirculating systems, the O2 is in the media: e.g. rockwool, perlite, grow rocks. Plentiful air space is available even after water is drained from the media. Roots thrive in O2-rich pockets. They are able to produce prolific root systems and plentiful root hairs to increase surface area to better absorb available ions. This is the best reason for using media with porosity. Of course, flood and drain systems suck fresh air into the media when it drains, which is why it’s such a great irrigation system.

In water-based recirculating systems, NFT, DFT and Aeroponics, O2 availability is intrinsic to the design of the system. NFT is a flat-bottomed tube with a shallow nutrient stream moving slowly, keeping root hairs moist and absorbing O2 (see “NFT Gro-Tanks,” UGM009). Aeroponics is misting droplets of water, increasing the surface area many-fold for roots to grow prolific root hairs for ion absorption. It supersaturates the solution with O2. DFT uses air pumps and water temp to keep roots bubbled with 02 and oxygen rich.

The heart of a media-based or water-based recirculating system is the nutrient reservoir. This too requires oxygenation, especially when water temperatures rise. The use of air pumps and air stones on smaller reservoirs and pump-powered eductors (venturis) on larger reservoirs make a big difference in pathogen suppression (nasty fungi and bacteria don’t like O2). This agitation drives ethylene gas from the solution and increases the longevity of the nutrient. Be sure that, if there are reservoir lids, there’s room for air exchange with ambient air in the room or greenhouse. Many commercial growers use fresh outside air in their eductors to keep the nutrient solution optimum.

Dissolved Oxygen (DO) can be measured to determine solubility of oxygen in fresh water. Fresh water at 72°F (22°C) has a DO of 8.7 ppm; at 82°F (28°C) it drops to 8.1 ppm. Salt solutions are lower. As a rule of thumb, every increase of 1ppm in DO is equivalent to an 11°F (12°C) temp drop. The cooler the temp, the higher the DO. You don’t want cold water on plant roots, though. You want 72°F (22°C) water at your roots for most plants.

When we measured DO in our greenhouse reservoirs, we found that a 74°F (23°C) nutrient tank at an EC of 2 had a DO of 6.3 ppm (low because of salts and sitting still). When we turned on an eductor (venturi), which we do in ALL reservoirs, we received a reading of 7.6 ppm. BIG difference. That’s an increase of 1.3 ppm without changing temperature.

Then we add an in-line Mazzei injector in between the tank and the feeder pipe, which raises DO to 8.3 ppm. By the time the water had run down the NFT channel and 18 plants had their way with the O2, with some off-gassing occurring, there was an 8.1 ppm DO left in the nutrient solution going back to the reservoir. That’s what we’re after! Plants thrive at those DO levels. Makes ALL the difference.

Be careful: as water temperatures of salt solutions increase, you must mitigate by adding O2 in the reservoir as well as directly on the roots. If you can’t get the DO level up by mechanical means, then you will most likely require a water chiller, which is expensive but sometimes imperative. If you cannot bring water temps down or increase DO in the nutrient solution, your next action will be disease suppression or inoculating roots with beneficials to out-compete the pathogens that thrive in high temp, low DO water. If you do get a DO meter, get a good one. We use an Extech Model 407510.

Light

Photosynthetically Active Radiation (PAR) light is a fancy term for the wavelengths plants use to vibrate chloroplasts to power the engine of photosynthesis, a vaguely understood process in my opinion. It is said that PAR light is in the 400 to 700 nanometer wavelength range. No big deal if you’re outside or in a well-lit greenhouse. But if you are growing under HID light or using it as a supplement, it certainly is.

Color temperatures of lamps are measured in degrees Kelvin from a color rendering index (CRI). The blue/white side of the spectrum has higher Kelvin temp: 6000K-8000K (MH lamps). The yellow/red side of the spectrum has lower Kelvin temperature: 3000K (HPS lamps). As a rule, the higher the Kelvin temp, the more vegetative the growth. The lower Kelvin temps are used for supplemental and/or flowering light. Different bulbs have different combinations or blends of gasses for better PAR value. Plants can be finicky and prefer one blend of light more than another. Trial and error, sometimes, is the only way to find out what your plants really like.

High Intensity Discharge (HID) lamps produce light when the gases inside the fused alumina tube are heated to the point of evaporation by high voltage electricity. This process forces the metal gasses to throw off a barrage of photons partly in the PAR range. As the bulb burns over time, the metal gasses slowly change form and degrade out of the PAR range. It is not obvious, but plant performance can suffer from lack of the PAR light when there is no shortage of photons to the naked eye. To look at light as a possible limiting factor, keep track of the hours your bulbs have been burning. If you are over the recommended burn range as stated by the manufacturer, that could be what’s compromising your system. Rule of thumb with HPS bulbs is to replace them every 12 months, and MH bulbs every 9 months, with HPS burning 12 hour days, MH burning 18 hour days.

Outside it’s obvious what limits light, like trees. But in greenhouses, if the glazing is dirty, that’s a big deal and that situation just creeps up on you. Depending on what you’re growing and what time of year it is, a dirty film can cut out as much as 30% of available light. If you are using an 85% transmission film and have 30% attributed to dirt, that’s 55%, basically shade cloth. In situations where there is too much light and plants are unable to cope with the leaf temperatures or solar radiation, a white or metallic shade cloth is preferable to black, as black can radiate heat back down on the plant canopy. A simple mistake easily avoided by many growers in double poly greenhouses is that the inflation fan is pulling inside air in between the films, thereby creating moisture that blocks light. You can tell by the droplets in between the films, or a haze. It is always recommended to use outside air for inflation. Of course, all of this is dependent on location, latitude, geography, plant in cultivation and skill/experience of the grower. We cannot cover all those variables in a brief article.

Temperature

Plant response to temperature is pretty obvious. It’s visible. Plants stop growing when root temps hit 58°F (14°C). Air temp can actually be cooler than 58°F, but when roots are cool, growth slows and stops even when air temp increases. When temps are too high, say 95°F (35°C) plus, depending on RH, air flow, light, kind, size, and age of a plant, they may stop feeding and spend their energy evaporating water from their stomata to cool down. Temperature must be managed to keep plants transpiring and active in the sweet spot.

Most temp controllers are effective, turning on fans for increased air exchanges, but when temps are too hot outside, air conditioners must be used. As a variable, though, temperature control is straightforward. It’s common knowledge that insects like very consistent temperatures and no air movement. Find which temperatures are your best high and low, and vary them morning, daytime and night. Keep an inhospitable environment for the pests without sacrificing plant performance: another dance to master.

Humidity

The two ways of explaining humidity are relative humidity (RH) and vapor pressure deficit (VPD). Most people are familiar with RH and use hygrometers so, for the purposes of this article, I will use RH.

In my experience, this is the one variable that most growers need to be more aware of. The dance between temp/humidity directly affects transpiration rates as poor transpiration opens the plant organism to disease and mineral deficiencies.

RH is the amount of water vapor present in the air expressed as a % of the amount needed for saturation at the same temperature. Here’s what that means: if the humidity is too high, e.g. 95% at 75°F, plants cannot transpire or evaporate enough water to pull minerals up the vascular system even with stomata wide open. This usually results in calcium (Ca) deficiency (remember, Ca is a non-mobile element and must be constantly supplied to growing tips) and plant stress, which increases their vulnerability to fungal intrusion.

If humidity is too low, 50% at 75°F, stomata will open in an attempt to evaporate water because of the low pressure around the leaf, but then close up to conserve cell pressure in the leaf. Plants stress as they cannot take in CO2 with closed stomata and growth stops as the plant is just trying to survive without going into wilt (i.e. loss of leaf turgidity from which it’s difficult to recover). Again the plant is vulnerable to disease and insects. These two extremes points will create a high probability of crop loss.

As a rule, at 75°F (24°C), if RH is below 60% you must add moisture to get to 75% (which is ideal), but stay below 85% to avoid stress and disease. At 85°F (29°C), if RH is below 70% you must add moisture to get to 80% (which is ideal), but stay below 90% to avoid stress and disease. As temperature rises, air holds less moisture. Steer your plants within these parameters for optimum plant performance.

When RH is too low, use a fogger or humidifier coupled with outside air exchanges. When outside air is too warm and dry, you will have to use some form of air conditioner (if that is the only way) to drop the temperature to increase the moisture-holding capacity of the air.

When RH is too high, raise temperature to reduce moisture saturation of air coupled with outside air exchanges. If outside air has too high of an RH, you will need a dehumidifier to pull water out of the air.

Transpiration is king. Monitoring transpiration rates and keeping them optimum with temp/RH manipulation is crucial. If you are outside of the temp/RH safe zones and don’t use some mechanical method of bringing them under control, you will always be fighting the results of that variable being unchecked. This is where high quality environmental controllers come in handy

You can buy the most expensive nutrients, goodies and gadgets available to grow your crop, but if your plants are unable to transpire and you don’t know that, you had best learn quickly or get a day job

Air Circulation and CO2

No matter what kind of controlled environment you’re running, greenhouse or greenroom, air circulation is another key component that is often overlooked until mildew takes out your crop or your plants starve from lack of CO2. The great outdoors takes care of all this, but inside you have to provide the controls or fall prey to what you didn’t know you didn’t know.

Rule of thumb: 60 air exchanges per hour. Not only do you need to flutter your plants with gentle breezes from an oscillating fan or horizontal air flow (HAF) fans in a greenhouse, but you must freshen the air with air exchanges from outside, taking advantage of the 385 ppm ambient CO2. The raw materials that PAR light makes into carbohydrates are CO2 and H2O. CO2 furnishes the carbon and oxygen, while water furnishes the hydrogen for the carbohydrate (CH2O).

If air exchanges are frequent, 385 ppm CO2 is plenty unless you’re looking to accelerate growth by enriching your space with higher levels to, say, 1500 ppm CO2. Even if you are adding CO2, you still must exchange air. There are numerous ways to provide CO2: chemical reactions, gas bottles, gas generators and a variety of controllers and monitors depending on the size of the operation. For the purpose of this article, you just need to know that it is a basic component of the indoor growing environment, and be mindful that it’s always available. Without CO2, plants will not grow.

One of my teachers, Grenville Stocker in NZ, took me into one of his client’s lettuce/herb greenhouses and asked me, “Would you get a chair, sit down, read a book or hang out in here all day?” Actually, it was way too moist, not enough air movement, my shirt was sticky, and it was uncomfortably warm. I said, “No way.” He remarked, “How do you think those plants feel? The same way, I reckon, except they can’t leave.” Then he showed me powdery mildew in certain areas, a thrip infestation and tip burn in some of the lettuces. The plants did not look vital, they looked stressed. I noticed the HAF fans were down, because of a blown breaker that the grower had been meaning to fix for a week. He had an RH monitor but no controller to check humidity and spill air or add heat … AND he was doing only 1 air exchange per hour because it was cold outside. He wanted to keep temps up inside without turning on the heat, which would cost him money. I looked at the RH: it was 95%. Temp was 80°F but it felt like 90°F because of the humidity. His client was too busy to pay attention or take coaching, and he wasn’t even there. Grenville always tested me; he’d say, “What’s wrong with this picture?” Then he would point out a basic that was obvious once I saw it. Most problems were easy to correct once distinguished.

I found out later the grower lost 50% of his crop and the other 50% was barely marketable. Had he kept HAF fans working, increased his air exchanges and turned up the heat to drive off the humidity with the help of a controller, he would not have had crop and financial loss. Just that one error cost him a market: he couldn’t deliver, so a competitor moved in. The point I’m making is: don’t leave your plants in an environment you can’t handle being in yourself. Use meters and controllers, but always keep them honest by paying attention to what your skin says.

All the variables of light, temperature, humidity, air circulation and CO2 must dance together in a harmony that you must monitor and control to be successful and avoid crop loss. If you cannot distinguish which variable is out, you will be guessing what the problem is and perhaps taking actions that are detrimental. Next time a problem arises (which inevitably will happen) and you’re scratching your head as to what to do, go through this list and check off each one that you KNOW is in tolerance. These 5 basics could be what you didn’t know you didn’t know. Now that you do, dissect them and become competent with each one:

The 5 basics of recirculation and plant performance:

1. Pure source water
2. Balanced nutrient ions/anions (EC)
3. Optimum pH
4. Plentiful oxygen availability
5. Optimum light/temp/humidity/air circulation/CO2

For the content and experiences that allowed me to write these articles, I’d like to thank my teachers, Grenville Stocker (Stocker Hort), Jeff Broad (AutoGrow), Genaro Calabrese (ex partner), Grant Creevey (Accent Hydro) and all our clients and associates for sharing and being open to “figuring it out.” Controlled environment plant cultivation is infinitely beguiling; I am always learning a greater respect for being part of that process. Genaro’s motto: “Every plant, every day.”

Good luck and good growing.

Michael Christian, the president of American Hydroponics since 1984, is a hydroponic system designer and consultant to commercial growers worldwide.

The basics – What is NFT?

NFT stands for Nutrient Film Technique. With this hydroponic system, plants grow in a purpose-built sloping channel with a fall of 1:40–1:50. Nutrient solution is pumped from a reservoir onto the channel where it passes over the plants’ roots and finally returns back to the reservoir. The roots on the channel develop to form a mat, which is partially in the shallow film of re-circulated nutrient solution, and partially above it. Utilizing this technique, the root mat growing in the nutrient film is supplied with essential water and nutrients, and the root mat above the film remain sufficiently moist with an abundance of oxygen.

The NFT system was developed between the 1960s and ’70s by Dr. Allen Cooper at the Glasshouse Crops Institute in the UK. In the early days, the growing channels were made in concrete floors. Today, growing channels are made from plastic and are often referred to as “trays” or “gullies.”

Why choose NFT?

Other than supplying your plants with the ideal root environment, NFT systems are incredibly efficient and environmentally friendly. The nutrient solution is recirculated for long periods: in some commercial applications, for many months. This continual recycling of the solution makes the most out of the water and nutrients you’re supplying. NFT systems also use very little growing media: just the small amount of substrate the plant is propagated in. This means that after each crop all you have to dispose of is a mat of roots, which easily biodegrades.

NFT Gro-Tanks

The system I will be demonstrating is called a Gro-Tank and is manufactured in the UK by Nutriculture.

The Gro-Tank is great for small-scale production as it has a wide top tray for the roots to grow on, with the reservoir directly beneath it spanning its whole length. A small submersible pump in the reservoir delivers nutrient solution to the tray above, which flows down the tray and back into the reservoir. This compact, self-contained design eliminates the need for lots of pipe work and is very low to the floor, making best use of the height available for tall/vining plants.

I have used the Gro-Tanks for many types of crops, including lettuce, basil, watercress, coriander, parsley, rocket, chard, chives, tomatoes, peppers, chillies, strawberries, cantaloupe melons, cape gooseberries, and many more. The diary below shows one of my NFT grows with cucumbers. I hope you enjoy…

Equipment

1 x heated greenhouse
1 x heated propagator
5 x starter plugs
5 x 4” rockwool blocks
1 x 604 Nutriculture Gro-Tank: 5ft x 1.5ft (153cm x 49cm) tray with 16 gallon (60L) reservior
1 x submersible adjustable pump
1 x submersible water heater
Spreader mat (capillary matting)
4 x roller hooks (plant supports)
Vine clips
Liquid nutrients and growth supplements

January 18th – Germination

I’m growing a cucumber variety called Carmen, which is an all-female F1 hybrid variety. The majority of cucumber varieties produce both male and female flowers; all we are interested in are the female flowers, as these develop cucumber fruit. This all-female (parthenocarpic) variety will develop a seedless fruit without the need for pollination. I found Carmen great last year for greenhouse growing as you don’t have to pick male flowers off and it produces large, full fruits.

I planted the seeds in starter plugs pre-soaked with a low-strength nutrient solution (EC 1.2) designed for seedlings and cuttings, and a liquid beneficial microbe additive. These were placed in a heated propagator and germination was fast!

Shown here is one cucumber seedling 8 days after planting. At this point they were transplanted into 4” rockwool blocks.

January 31st – Propagation

Considering it’s been 21 days since I planted the seeds, I’m happy with the way they’re progressing. They are now being watered with nutrient solution (EC 1.4, pH 5.8) every 2-3 days. The roots are doing really well and can be seen on the top of the block.

Without the block covers, algae would be taking over and the roots would not be growing so well on the surface. The natural light entering the greenhouse is being supplemented with 220W fluorescent strip lights. These plants should be ready for their NFT system in about 1 week.

February 4th – Growing on

The plants now need nutrient solution every day and the roots are clearly visible all over the bottom of the block. I also have increased the EC to 1.6. They will need to be planted in the next few days.

February 5th – Setting up

These cucumber plants are now 26 days old and are ready to go onto their final system, which will be an NFT Gro-Tank.

The most important thing about getting plants ready for NFT systems is to ensure they are well-established and have a mass of healthy white roots. Without this mass of roots inside the rockwool block, the plant will not be able to cope with the continuous irrigation of the NFT system. These plants have been propagated using an air pruning technique (see “Power Propagation” UGM0005) to ensure the rockwool block is packed full of roots.

This is the Gro-tank I will be using (below). It is called a 604. Nutriculture, which makes the system, also makes 5 other size variations to suit any grow area. The top tray is where the plants are placed and the reservoir underneath stores 16 gallons (60L) of nutrient solution.

The Gro-Tank has one delivery tube where the nutrient solution is pumped onto the tray using a small submersible pump with an adjustable output:

To ensure an even distribution of nutrient solution on the tray, I use capillary matting, aka “spreader mat.” The system manufacturers recommend using spreader mat and supply it with the system. One layer is enough. After laying it out, I fill the reservoir with water that has been standing in a storage tank for a few days: this allows some chlorine to be evaporated and, more importantly, allows the temperature to rise. Tap water in February in the North of England usually comes out ice cold and will seriously stress plants if used.

Once the tank is filled I turned the pump on and slow the output down so the solution lands in the middle of the first diamond. This provides a flow rate of approximately 1 quart (1L) per minute. Recommended flow rate for NFT systems can be anywhere between 13.5oz to 2 quarts (400ml to 2L) per minute. Determining flow rate in NFT systems usually depends on channel length; if you have very long channel lengths you will need larger flow rates. You could probably write a thesis on other variables that will determine the required flow rate for NFT, but I find that as long as nutrient solution flows as a shallow film and does not “puddle,” the plants grow well.

After a few minutes of the pump running, the spreader mat wets throughout the tray. I always run the pump and observe the way the water is flowing down the tray. I have found from experience that if the Gro-Tank is not placed on a level floor then some areas of the tray will develop puddles and other parts will remain dry. Leveling out the tank with thin pieces of plywood usually sorts out an uneven floor. Luckily, the floor is fine and I’m happy to “go with the flow.”

Now that I know the flow down the tray is perfect, I cut out the planting holes in the corriboard cover. Corriboard is twin-walled, semi-rigid plastic sheeting. It prevents any light from reaching the roots and can help provide a bit of support for the plants. I’m planting 4 plants in the Gro-Tank, so I cut the holes accordingly.

Providing support for large plants is very important. To support my cucumber plants I use roller hooks, which are a spool of string on a wheel attached to a support hook. The vines are trained up the string with the help of plastic vine clips. When they grow tall enough to reach the wheel, string is let out, which lowers the vine. This support hook is then moved along so the excess vine at the bottom rests on the corriboard. Using this technique, one of my cucumber plants last year was 49 feet (15m) long!

Another popular way to support plants on NFT systems is using netting, which is stretched out horizontally on a frame above the plants so that when they grow into it they are supported by the net.

Before planting onto the tray I remove the plastic wrapper from around the block. When I was learning how to grow using NFT systems I was told by a more experience grower at the time to “leave the wrapper on, otherwise the block will fall apart.” After a few crops I decided to experiment so I slid the wrapper up the block exposing the bottom third. This helped with initial establishment and root growth from the block, which I believed was a factor in achieving a more successful crop. The next crop I decided to risk it and remove the wrapper completely and, instead of the block falling apart, I got quicker establishment and a much better root mat. The block lasted the whole season, staying completely intact. Not surprisingly, I don’t follow this grower’s advice anymore.

Once the roller hooks are in place, I tie the string around the rockwool blocks and place them into position:

The positioning of the blocks on the tray is fairly important: I find staggering the plants works best. This allows the nutrient solution to flow uninterrupted through the mid-section of the tray, which helps once the root mat has built up. I also find that positioning the blocks so that the solution can flow through the grooves on the bottom of the block helps with establishment.

Then I place the corriboard and black and white sheeting back on the tray and lower the plants into their pre-cut holes. I cut the black and white with an X so the folds can be repositioned over the top of the block to cover it and prevent algae growth.

Now that the plants are in their system, I add a “grow” nutrient to the water in the reservoir at an EC of 1.6 and a pH of 5.8. I also add a strong dose of beneficial microbes to the mix to aid with root growth and disease prevention.

I put a submersible water heater in the tank and set the thermostat to 64°F (18°C). I also plugged in the pump, which I will now leave alone to run 24/7. Some growers plug their NFT pumps into a segmental or interval timer. This “pulse feeding” is not the strategy Dr. Allen Cooper conceived when he developed NFT, but some people growing plants with more sensitive root systems or who use large propagation blocks find it helps. It’s very important when implementing pulse feeding that the root mat never approaches a dry state. I have contacted Nutriculture about pulse feeding, and they only recommend that the pump is run 24/7.

These cucumber plants should settle in and start growing vigorously in the next few days. Hopefully I should be picking my first fruits in no time.

February 14th – Vegetative Progress

In 11 days these cucumbers on the NFT Gro-Tank have more than doubled in height and they are establishing well into their system. I have attached them to the string using plastic vine clips, which clip onto the string and hold the vine in place.

I have been routinely checking the nutrient solution pH and EC every 1-2 days. The pH was rising by 0.2 points every 2-3 days. As the pH reached 6.2-6.4, I added phosphoric acid to bring it back to 5.6-5.8. I like to let the pH drift a bit rather than keeping it within a tight range: as long as it doesn’t go higher than 6.5 or lower than 5.5, I’m not worried.

Usually I find the nutrient strength stays stable or increases slightly as the water level drops, but over the past 11 days the plants have used approximately 4 gallons (15L) of nutrient solution and the EC has dropped to 1.2. This is an indication that the plants are hungry, so I top up the reservoir with water and increase the nutrient strength to an EC of 1.8. Whenever I add anything to the tank I disconnect the delivery tube from the tray and submerse a larger 265 gallons/hour (1000L/hour) pump in the reservoir to mix the solution. Once the nutrient solution is corrected, I reconnect the delivery tube.

I always estimate how much water I add back to the tank and take a mental note. Once I know I’ve added back roughly the same volume as the tank holds (16 gallons / 60L) I will consider running the reservoir down to half full, emptying the tank, and refilling it with fresh water and nutrient solution.

Many growers change out the nutrient solution every week, regardless of how much the plants are using. I find this a bit unnecessary and like to base my solution change-outs on how the plants are using it.

The pictures below show how well the roots are extending from the rockwool blocks. Soon there will be a thick mat of roots all over the tray:

February 25th – Flowers and Fruits

It always amazes me how fast plants grow in a productive environment using hydroponic systems, but cucumbers are a whole other ball game. In 11 days they have more than tripled in size and burst into flower. One fruit is already quiet large and will be ready in a few days.

They have also started sending out tendrils and growing side shoots. I remove both but keep a few side shoots for cutting material and put them in my aeroponic propagator.

The greenhouse environment is pretty easy to maintain this time of year. The heating keeps the night-time temperature around 64°F (18°C) and the top vents ensure the day temp does not exceed 77°F (25°C). I have 2 centrifugal humidifiers running to keep the relative humidity between 60-70%.

The plants are now using 1.5-2 gallons (6-8L) of nutrient solution per day and I make sure I top up the reservoir frequently. It’s better to have a full tank as it provides a better buffer for changes in pH and EC. The plants seem happy with the nutrients at 1.8 EC so I’ll leave things be.

One thing I love about NFT is that you don’t have to think about irrigations. The pump is on a slow trickle, and that’s all that matters.

The cucumber fruit develops behind the un-pollinated female flower.

February 27th – Nutrient tweaking

We have had a few warmer, brighter days recently and the plants are loving it. The first large fruit is growing well but is showing signs that I need to tweak the nutrient slightly. You may notice in the picture below that the bottom of the cucumber is slightly more bulbous than the top. The leaves of the plants are also showing a faint yellowing (chlorosis) around the edges. This is a sign that the plant requires more potassium.

To increase the potassium in the solution I add a blooming additive high in potassium and phosphorus at the rate of 1 ml per L. Before adding this I top up the tank with water, add the PK booster, then add more base nutrient to bring it back to 1.8.

You may also notice some loose vermiculite on the tank and floor. I have introduced the predatory insects Phytoseiulus persimilis, which come in a vermiculite carrier. I noticed a small outbreak of spider mite on some peppers on the other side of the greenhouse, so as a precaution I sprayed all the plants in the greenhouse with a natural-contact insecticide that works by suffocation, not chemicals. A few days after spraying, I introduced the predators to clean up any lingering spider mites. I will now introduce a bottle of 2000 Phytoseiulus persimilis every 4 weeks throughout the greenhouse and keep spraying to a minimum.

February 29th – Roots going mad

The roots are really growing well now and starting to develop to form a mat in places. I like to regularly inspect the roots in the NFT system, mainly because you don’t get to do it with other systems!

March 3rd – Plant Training

The plants have now reached the full height of the greenhouse so I let out a small amount of string and lower the vines.

Once I have lowered these a few times I will move the roller hooks clockwise around the Gro-Tank. The stems rest on top of the corriboard. I started using this training technique with my tomatoes and tried it with cucumbers. I find it works pretty well but most commercial growers implement an umbrella training system. I have yet to try it but will get around to it one day.

March 11th – New plants!

The side shoots I took off 2 weeks ago are now rooted plants and are ready for transplanting.

I have to say, aeroponic propagators are great. I have one running continuously in the corner of my greenhouse and just put shoots in and forget about them. 1-2 weeks later you have cuttings. Can’t get any easier.

March 14th – The Bumper Crop

The plants have definitely responded well to the PK booster. The leaves are now dark green all over and the fruits have developed to be large, full and evenly shaped. Some are slightly curved but it adds to the character!

I’ve had 3 cucumbers off the plants so far, but today I picked 6 ripe fruits in one go. From here on out I guarantee I will have so many cucumbers that I will make myself and all my friends sick of the sight of them!

March 26th – Growing on

The cucumbers have been growing well and are now producing ripe fruit at a steady rate of two to three cucumbers every four days. They could try and produce more but I remove developing fruits once there are more than 4 developing on each vine. If there is a high fruit load on the plant, developing fruits will abort. The weather is starting to warm up and the greenhouse is now thriving from the increased day lengths and light intensity. Bring on summer!

Looking Ahead

Recognizing the environmental conditions and adjusting the nutrient solution is part of my ongoing management strategy for recirculating systems. As warmer weather comes along in May and June I will certainly see the EC rising every few days in the reservoir. As this starts to happen I will dilute the EC slightly to around 1.6.to compensate.

Water uptake will certainly go up too so I will have to make sure I regularly top up the reservoir once a day. I also make sure I service my pump every 2 months. This is fairly quick and easy to do and will give me peace of mind that it’s in good working order.

Interested in NFT and want to learn more? If you missed Everest’s introduction to NFT and grower’s tips in UGM0009, check it out here!

What are Aphids?

Aphids (aka plant lice) are soft- bodied, pear-shaped insects that feast on your plants. Outdoors they are most prevalent during the spring and summer seasons. Aphids are common garden pests – the green variety is the most well-known, although they can also take pink, brown, yellow and black forms. In all, there are over 200 species of aphids. Some varieties are quite specific to certain plant groups, whereas most are not that fussy and will munch on a wide variety of different plants. Aphids are capable of asexual reproduction and can spawn throughout most of the year, sometimes producing nearly 100 young per aphid in the course of just one week! Indoor growers need to be especially wary of aphids. If you don’t spot them early, a relatively small intrusion will soon turn into a massive infestation unless you act quickly.

What’s the Damage?

Aphids injure your plants by puncturing plant stems and stalks with their skylets – powerful suction devices built into their mouths. Their goal is to find some plant sap which, once located, they suck mercilessly, gorging themselves at the plant’s expense. Prolonged aphid attacks will considerably weaken your plants. Common telltale signs of aphid damage include curled, discolored, and deformed leaves. Also, keep an eye out for “sooty mold” which is caused by mold colonies feeding off the sticky waste the aphids leave behind after their feeding frenzy. If all that isn’t enough, aphids can also spread incurable plant diseases. In short, aphids SUCK big time!

October 23

The wind began gusting with enough force to knock down my outdoor tomato plants. In order to save them, I had to continually move them in and out until the gusting ceased. It didn’t take long until the task of moving 40+ pots from the front yard into my two-bedroom apartment became onerous and inconvenient. Confronted with a living room and kitchen full of plants, I had no other place to put them than right in front of the door to my indoor garden. There (and everywhere in the house), my outdoor plants were spared from the 50-mile/ hour winds outside. I left them there for just over an hour. The strong winds passed so I proceeded to return all the plants outdoors. Little did I know that this would be the dumbest, most destructive thing I had ever perpetrated on my beloved tomato plants.

October 24

I woke up and began my regular morning watering of my outdoor plants. During this activity it’s not uncommon for me to spot the occasional caterpillar or earwig enjoying its breakfast, but today was different. Instead, I stumbled upon a family of aphids nesting on my tomato leaves. Temperatures had begun to hang in the 50s and 60s, and I was expecting the usual aphid wave that comes in the fall. So when I saw the little critters, I thought “well, the wave is here. I’ll start squishing aphids and wipe them out with some neem oil. No big deal.” And so I focused my attentions on pest control for my outdoor plants. And it worked! In less than two days’ time, my tomatoes appeared to be completely pest-free. Fortune, it seems, is not without a sense of irony.

October 28

Today was reservoir change day, always a logistically challenging endeavor considering how little room I have to move around in. First step is to empty my indoor garden of plants so that I stand a chance of reaching the ebb and flow table positioned against the far wall of my walk-in grow closet. As I moved and inspected the plants from the mid-section of the room I began to notice some light green bumps on the leaves of my sweet banana peppers. I got up close and saw these shiny, six-legged little critters standing on the leaves, their antennae bent towards their backs, gross-looking, and engaging in some serious sap-sucking. APHIDS! And if experience told me anything I knew that there were probably plenty more to be found. Sure enough, my heart sank when I discovered that all of the pepper plants on my ebb and flow table were populated with aphid “families.” Everything from my Dorset Nagas, my Ajíes Dulce and Caballeros, my Bhut Jolokias, and (oh, noooo!), some pimento plants that came from seeds saved by my late Grandmother – everything was covered in aphids! Panic eventually gave way to pragmatism. The remainder of the day was mostly taken up with bug-squishing and a frenzy of neem spraying. The reservoir change was postponed for another day or two. I had more pressing matters to attend to!

October 31

(photo courtesy of Flagstaffotos)

I woke up determined to get that reservoir change out of the way. I ventured into the bowels of my indoor garden and began to remove the plants from the tray as before. This revealed just how badly infested my plants were: colonies of aphids had pitched tents all over the plants’ leaves, stems and shoots. All of the lower leaves were suddenly looking really crappy: some had begun to show brown spots and the spotting looked like it was creeping upwards toward the plant canopy. Now I had a disease to identify on top of my aphid problem! It was not long before I identified the leaf spotting to be Anthracnose, a viral plant disease (for which there is no cure), which is often carried by aphids. That’s when the seriousness of the matter really struck home. My beautiful pepper plants were screwed. Even if I were to effectively eradicate what was now a full-blown plague of aphids, I’d still be left with sick plants! I’d screwed up royally by breaking that one important rule: Never bring outdoor plants into your indoor garden! If you absolutely have to, make sure they first undergo a lengthy quarantine period!

The plants had to be destroyed. Man, I was gutted. It didn’t matter so much that my Nagas were in the midst of setting fruit or that my pimentos had a special significance — all my infected plants had to be killed. So I took my camera and snapped a few shots of the unwanted guests and, without making too much of a stir, began to hack and bag branches until only the plants’ stems were left. All the containers were dumped – substrate n’ all – into a reinforced garbage bag. All infected plant matter was then doublebagged and immediately thrown in the dump outside. The reservoir was emptied and bleached thoroughly. The rest of the plants in my indoor garden were thoroughly inspected. Some contained one or two aphids, and were cleared of all visible pests and removed from the indoor garden. I sprayed a 10% bleach solution on the walls, floor and ceiling. All equipment inspected and sterilized. An hour of sparing an outdoor plant from wind damage had already compromised my whole indoor grow. This time I would leave nothing to chance.

After my indoor garden was cleaned, I re-checked all the plants and decided to just do away with any seedlings that showed signs of aphids or anthracnose. It would not be worth the time, effort and money to raise a plant that was doomed from the start. The rest of the plants were sprayed with neem oil in order to slow down the life cycle of any aphid youngling I could not catch. Inspections were performed daily until the problem was under control; I scheduled neem oil treatments every 3rd day, but this ended up being performed every other day due to the resurgence of young aphid colonies. Some leaves were beginning to appear rather leathery – probably because of the excess spraying of neem oil. At the end of that week I discovered some aphids nesting on the young shoots of my baobab tree. No other aphid affront had been this cheeky. I don’t mind admitting that the sight of more aphids at this point tipped me over the edge. It was time to call in the big guns.

November 2

I marched to my local hydro shop and made a beeline for the pest control aisle. There I picked up the largest can of pyrethrin-based spray. The store owner seemed surprised to see me buy a can of bug spray because I am a neem-type guy, so I let him in on the battle that was taking place in my indoor garden. He assured me that I had done all I could and that the bug spray would definitely take care of the problem. Once back home, I inspected all the plants and manually killed as many aphids as I could spot – only a handful at this point. This was good news as it indicated to me that the bulk of the infestation had been eradicated by disposing of the infected plants. Now my task was to prevent a re-infestation. In order to achieve this I had to do more than merely reduce their numbers: they needed to be obliterated!

The pyrethrin spray was applied after the lights went out, using short bursts and kept 1-2 ft away from the plants. This would ensure a more ample, gentler coverage while still delivering the pyrethrins to any potential pests. I sprayed my plants once again during mid-week and decided to wait a few more days and re-evaluate its effectiveness. My concerns about burning the plants dissipated throughout the upcoming week, as none of my plants showed signs of contact burn. Not only that, but I was seeing fewer & fewer aphids around the area, and my baobab tree exhibited none by the end of the week. Having seen good results from the pyrethrum spray, I decided to incorporate it into my pest control program. From then on, I would be lightly (but thoroughly) spraying my plants on a weekly basis.

Lessons Learned

There are lessons to be learned and relearned from our mistakes. My first mistake was the breaking of this most-important rule: Never bring outdoor plants into your indoor garden without first undergoing a quarantine period. You can also say that I screwed up by not destroying the pepper plants immediately after finding the first aphids indoors. But then again, no signs of Anthracnose were initially observed. I should have erred on the side of caution and assumed that where there are aphids, diseases follow. My third mistake was over-applying neem oil. Neem did not burn my plants, but it certainly turned my leaves hard and leathery (and I do not know if that is a good thing for their tiny, delicate stomata). However, all in all, I think I was lucky to have been able to control it by using pyrethrin; otherwise, all my plants would’ve been for the trash!

Moment of silence for Eliab’s loss. Now … got an aphid-assaulting tip or horror story you care to share? Post it below!

Source: Institute of Science in Society

“Major crops genetically modified for just two traits – herbicide tolerance and insect resistance – are ravaged by super weeds and secondary pests in the heartland of GMOs as farmers fight a losing battle with more of the same; a fundamental shift to organic farming practices may be the only salvation.”

- Dr. Mae-Wan Ho, Institute of Science in Society

Two traits account for practically all the genetically modified (GM) crops grown in the world today: herbicide-tolerance (HT) due to glyphosate-insensitive form of the gene coding for the enzyme targeted by the herbicide, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), derived from soil bacterium Agrobacterium tumefaciens, and insect-resistance due to one or more toxin genes derived from the soil bacterium Bt (Bacillus thuringiensis). Commercial planting began around 1997 in the United States, the heartland of GM crops, and increased rapidly over the years. By now, GM crops have taken over 85-91 percent of the area planted with the three major crops, soybean, corn and cotton in the US [1]] (see Table 1), which occupy nearly 171 million acres.

Table 1. GM crops grown in 2009 in the USA

The ecological time-bomb that came with the GM crops has been ticking away, and is about to explode.

HT crops encouraged the use of herbicides, resulting in herbicide-resistant weeds that demand yet more herbicides. But the increasing use of deadly herbicide and herbicide mixtures has failed to stall the advance of the palmer super weed in HT crops. At the same time, secondary pests such as the tarnished plant bug, against which Bt toxin is powerless, became the single most damaging insect for US cotton.

Monster plants that can’t be killed

It is the Day of the Triffids – not the genetically modified plants themselves as alluded to in John Wyndham’s novel – but “super weeds that can’t be killed” [2], created by the planting of genetically modified HT crops, as seen on ABC TV news.

The scene is set at harvest time in Arkansas October 2009. Grim-faced farmers and scientists speak from fields infested with giant pigweed plants that can withstand as much glyphosate herbicide as you can afford to douse on them. One farmer spent US$0.5 million in three months trying to clear the monster weeds in vain; they stop combine harvesters and break hand tools. Already, an estimated one million acres of soybean and cotton crops in Arkansas have become infested.

The palmer amaranth or palmer pigweed is the most dreaded weed. It can grow 7-8 feet tall, withstand withering heat and prolonged droughts, produce thousands of seeds and has a root system that drains nutrients away from crops. If left unchecked, it would take over a field in a year.

Meanwhile in North Carolina Perquimans County, farmer and extension worker Paul Smith has just found the offending weed in his field [3], and he too, will have to hire a migrant crew to remove the weed by hand.

The resistant weed is expected to move into neighbouring counties. It has already developed resistance to at least three other types of herbicides.

Herbicide-resistance in weeds is nothing new. Ten weed species in North Carolina and 189 weed species nationally have developed resistance to some herbicide.

A new herbicide is unlikely to come out, said Alan York, retired professor of agriculture from North Carolina State University and national weed expert.

Glyphosate-resistant weeds from widespread planting of HT crops

Glyphosate is the most widely used herbicide in the US and the world at large. It was patented and sold by Monsanto since the 1970s under the trade name and proprietary formulation, Roundup. Its popularity shot up with the introduction of HT crops. Data from the US Department of Agriculture indicate that the use of glyphosate on major crops went up by more than 15 fold between 1994 and 2005 [4]. The EPA estimated in 2000-2001 that 100 million pounds of glyphosate are used on lawns and farms every year [5], and over the last 13 years, it has been applied to more than a billion acres [6].

It did not take long for glyphosate-resistant weeds to appear, just as weeds resistant to every herbicide used in the past had appeared. The Weed Science Society of America reported nine weed species in the United States with confirmed resistance to glyphosate [6]; among them are strains of common ragweed (Ambrosia artemisiifolia), common waterhemp (Amaranthus rudis), giant ragweed (Ambrosia trifida), hairy fleabane (Conyza bonariensis), horseweed (Conyza canadensis), Italian ryegrass (Lolium multiflorum), johnsongrass (Sorghum halepense), rigid ryegrass (Lolium rigidum), and palmer pigweed (Amaranthus palmeri).

Glyphosate-resistant palmer super weed

Glyphosate-resistant palmer pigweed first turned up in late 2004 in Macon County, Georgia, and has since spread to other parts of Georgia as well as to South Carolina, North Carolina, Arkansas, Tennessee, Kentucky and Missouri [7]. An estimated 100 000 acres in Georgia are severely infested with pigweed and 29 counties have now confirmed pigweed resistance to glyhosate, according to weed specialist Stanley Culpepper at the University of Georgia. In 2007, 10 000 acres of glyphosate-resistant pigweed infested land were abandoned in Macon County.

Monsanto’s technical development manager Rick Cole was reported saying that the problems were “manageable”. He advised farmers to alternate crops and use different makes of herbicides. Monsanto sales representatives are encouraging farmers to mix glyphosate and older herbicides such as 2,4-D, banned in Sweden, Denmark and Norway on account of links to cancer and reproductive and neurological damages. It is a component of Agent Orange used in Vietnam in the 1960s.

Farmers in Georgia are reported to be going back to conventional non-GM crops.

Weed scientists at the University of Georgia estimate that an average of just two palmer amaranth plants in every 6 m length of cotton row can reduce yield by at least 23 percent [8]. A single weed plant can produce 450 000 seeds. Many fields in Arkansas, Tennessee, New Mexico, Mississippi and most recently, Alabama are also infested.

Paraquat is recommended for use in conservation tillage programmes, mixed with up to three other herbicides, each with a different mode of action. Scientists at the University of Tennessee have seen palmer weeds resistant not only to glyphosate but also to the sulfonylurea herbicide trifloxysulfuron-sodium.

Glyphosate resistance with the greatest of ease

Critics have been predicting glyphosate-resistant weeds before HT crops were introduced, simply through cross-pollination between HT crops and wild weedy relatives. But they had neglected the ‘fluid genome’ mechanisms that can alter genomes and genes in response to environmental stimuli, enabling most weed plants to become herbicide resistant independently of cross-pollination. I drew attention to these mechanisms in my book Genetic Engineering Dream or Nightmare, the Brave New World of Bad Science and Big Business [9] first published in 1997/1998.

Researchers led by Todd Gaines at Colorado State University, Fort Collins in the United States investigated glyphosate-resistant palmer pigweed populations from Georgia. They found that the gene coding for the enzyme EPSPS responsible for metabolising glyphosate herbicide was amplified (multiplied) 5 to 160-fold in glyphosate-resistant plants compared with glyphosate-susceptible plants [10]. The level of gene expression was positively correlated with gene copy number. Fluorescent staining for the gene showed that the amplified gene copies were present on every chromosome.

Gene amplification is one of the most common physiological responses of cells and organisms to ‘selective’ agents in their environment, known at least since 1980s [9].

Glyphosate resistance has been confirmed in 16 weed species as of 2009 [10]. The mechanisms identified so far include reduced glyphosate uptake, and/or mutations in the EPSPS gene that make it less susceptible to inhibition by the herbicide. Glyphosate-resistant palmer pigweed is the first case of resistance based on gene amplification. It confirms the ease with which resistance to obnoxious agents can evolve [9], and the futility of this ‘chemical warfare’ against nature.

Tarnished plant bug the single most damaging pest for cotton

The tarnished plant bug infested 4.8 million acres of US cotton in 2008 [11] making it the single most damaging pest for cotton. Another insect, the fleahopper ranked 5th, and infested 2.3 million acres.

The Cotton Belt of the United States, extending from the San Joaquin Valley of California to Southeastern Virginia, has largely seen off the boll weevil and tobacco budworm since the introduction of Bt cotton, which now accounts for 65 percent of the area planted with cotton (Table 1 [1]). But, as in India and elsewhere [12, 13] (Farmer Suicides and Bt Cotton Nightmare Unfolding in India, Mealy Bug Plagues Bt Cotton in India and Pakistan, SiS 45), secondary pests are posing serious problems, especially the tarnished plant bug.

The tarnished plant bug (TPB), Lygus lineolaris, has been a cotton pest for as long as records were kept. Before 1995, it was controlled with insecticides targeting other insect pests such as tobacco budworm and boll weevil. According to researchers at the Mississippi State University Delta Research and Extension Center [14], since the widespread adoption of Bt-cotton and eradication of the boll weevil, less insecticide have been used; and as a result, the tarnished plant bug has become the primary insect pest of cotton.

Additional insect control costs are coming from increasing foliar sprays, higher technology fees and pest resistance, said Jeff Gore, research entomologist at the Delta Research and Extension Center, speaking at the 2010 Beltwide Cotton Conferences in New Orleans [15]

In 1995 planting an acre of cotton cost $12.75 to $24; in 2005, planting Bollgard, Roundup Ready cotton with a ‘Cadillac’ seed treatment would have cost about $52 an acre. Now in 2010, with Bollgard II and Roundup Ready Flex, farmers will be spending $85 or more an acre.

“In Mississippi, we have growers who are spending well over $100 for foliar insect control. You add that onto technology fees and seed treatments, you understand why our cotton acreage is decreasing.” Gore said.

To compound the problem, TPB has become resistant to several classes of insecticides, particularly in the Delta regions of the Mid-South states [14].

While TPB is a pest of cotton throughout the growing season, it is particularly damaging during the flowering period, when the pest reproduces copiously, so both adult and immature stages of TPB feed on cotton during the flowering period. Most feeding occurs on reproductive structures. The pests insert their mouthparts into squares and small bolls. It is not uncommon for TPB to cause near-total crop loss in the absence of effective control in some areas of the Delta.

Mid-South growers consulted Gore about planting a non-Bt variety, especially with the higher costs of Bt technology [15]. “We have a few growers planting small acreages of non-Bt cotton, and they’re probably going to see benefits from that.

“But if we start shifting back to non-Bt cotton, I promise you, the tobacco budworm will come back, and we don’t want to be making foliar applications for resistant tobacco budworms, in addition to treating tarnished plant bugs. The amount of money we would have to spend in that situation would be astronomical.”

TPB has been the No. 1 pest in the Mid-South for the past four to five years, and is driving a lot of cotton growers out of the Mississippi Delta, no longer able to afford the cost of sprays.

Gore revealed that spider mites are also gaining a reputation as ‘budget busters’ in the South, along with aphids and stink bugs.

Like TPB, spider mites are becoming resistant to the insecticides used to control them. “Over the past 15 years, we’ve essentially doubled our application rates with Bidrin and tripled our application rates with acephate. So we’re not only spraying more often, we’re applying higher rates that cost more.” Gore said.

He pointed out that a side-effect of relying on neoniccotinoids for plant bug control is some resistance has developed in cotton aphids. “We’re starting to hear lots of complaints from consultants across the Mid-South.”

More of the same is futile

It is disappointing though predictable that the only official academic advice given to farmers is more of the same conventional practices that created the problems in the first place, spraying more and spraying mixtures of different kinds of pesticides, including those banned for being too toxic. Industry, meanwhile, is ready to sell varieties with more stacked GM traits; up to eight at double the seed price [16].

Disappointing too is the persistent effort by some governments and government scientists to promote the failed GM technology, which as I made clear, was already obsolete since the early 1980s [9]. A Sciencexpress paper (indicating quick publication, probably without peer review) entitled “Food security: the challenge of feeding 9 billion people” [17] co-authored by UK chief scientist Prof. John Beddington among others, while somewhat dismissive of current GM crops, nevertheless holds out promises we’ve heard for more than 30 years. “The next decade will see the development of combinations of desirable traits and the introduction of new traits such as drought tolerance. By mid-century much more radical options involving highly polygenic traits may be feasible.” It went on to promise “cloned animals with engineered innate immunity to diseases” and more.

Glyphosate and Roundup, still advertised as ‘less toxic to us than table salt’ in a pamphlet from the Biotechnology Institute promoting HT crops as ‘Weed Warrior’ [18], is in fact highly toxic as new findings indicate [19, 20] (Death By Multiple Poisoning, Glyphosate and Roundup, SiS 42; Ban Glyphosate Herbicides Now, SiS 43). Thirteen years of GM crops in the USA has increased overall pesticide use by 318 million pounds [21] (GM Crops Increase Herbicide Use in the United States, SiS 45). The extra disease burden on the nation from that alone is considerable.

India has learned bitter Lessons from Bt Cotton [22] in a saga of worsening farm suicides and, in common with the USA, an ecological disaster in secondary and new cotton pests, resistant pests, new diseases, and above all, soils so depleted in nutrients and beneficial microorganisms that they would cease to support the growth of any crop in a decade. Their only salvation is a return to organic agriculture, which has already proven far more sustainable and profitable than Bt cotton [12]. This may apply also to the USA.

A fundamental shift in farming practices needed now

The organic market has been booming in the United States despite the economic downturn. According to a new report from the US Department of Agriculture, retail sales of organic food went up to $21.1 billion in 2008 from $3.6 billion in 1997 [23] (see Fig. 1). The market is so active that organic farms have struggled at times to produce sufficient supply to keep up with the rapid growth in consumer demand, leading to periodic shortages of organic products.

Figure 1 Growth in US organic market 1997 to 2008

Certified organic acres more than doubled from 1.3 million acres in 1997 to a little over 4 million acres in 2005 (0.5 percent of all agricultural land in the US). In the same period, the number of organic farms increased from 5 021 to 8 493, and the average size of certified organic farms went from 268 acres to 477 acres.

So why are US farmers failing to taking advantage of the rapidly expanding market? It is thought [23] that potential organic farmers may opt to continue with conventional production methods because of “social pressures from other farmers nearby who have negative views of organic farming”, or because of an inability to weather the effects of reduced yields and profits during the transition period. This is not surprising on account of the persistent negative propaganda carried out by GM proponents, including government regulatory agencies, against organic agriculture. (See for example the recent attempt by UK Food Standards Agency to prove organic food is no more nutritious than conventional food, which backfired [24] (UK Food Standards Agency Study Proves Organic Food Is Better, SiS 44). The usual claims are that organic agriculture yields less and require more energy than conventional agriculture, and organic produce no more nutritious or healthy, but less hygienic than conventional produce. These false claims are all thoroughly refuted in ISIS report Food Futures Now: *Organic *Sustainable *Fossil Fuel Free [25], with evidence from the published scientific literature, as well as other studies.

Most relevant for US farmers is a study by Kathleen Delate of Iowa State University and Cynthia A. Cambardella of the US Department of Agriculture assessing the performance of farms during the three-year transition it takes to switch from conventional to certified organic production [26]. The experiment lasting four years (three years transition and first year organic) showed that although yields dropped initially, they equalized in the third year, and by the fourth year, the organic yields were ahead of the conventional for both soybean and corn.

Our report [25] also documents the enormous potential for reducing greenhouse emissions – even to the extent of freeing us entirely from fossil fuels – through organic agriculture and localised food (and renewable energy) systems. It is a unique combination of the latest scientific analyses, case studies of farmer-led research, and especially farmers’ own experiences and innovations that often confound academic scientists wedded to outmoded and obsolete theories, of which GM technology is one glaring example.

At about the same time our report was released, the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD) was also published. IAASTD was the result of three-year deliberation by 400 participating scientists and non-government representatives from 110 countries around the world [27]. It came to the conclusion that small scale organic agriculture is the way ahead for coping with hunger, social inequities and environmental disasters [28] (“GM-Free Organic Agriculture to Feed the World”, SiS 38).

A fundamental shift in farming practice is needed right now, before the agricultural meltdown is complete.

References

1. Adoption of genetically engineered crops in the U.S.: Extent of adoption. USDA Economic Research Service, 1 July 2009, http://www.ers.usda.gov/Data/biotechcrops/adoption.htm
2. Super weed can’t be killed, abc news, 6 October 2009, http://abcnews.go.com/Video/playerIndex?id=8767877
3. “N.C. farmers battle herbicide-resistant weeds”. Jeff Hampton, The Virginian-Pilot. 19 July 2009, http://hamptonroads.com/2009/07/nc-farmers-battle-herbicideresistant-weeds
4. Who benefits from gm crops? The rise in pesticide use, executive summary, Friends of the Earth International, Amsterdam, January 2008.
5. 2000-2001 pesticide market estimates: usage, U.S. Environmental Protection Agency, http://www.epa.gov/oppbead1/pestsales/01pestsales/usage2001_3.htm
6. Glyphosate-resistant weeds: can we close the barn door? Weed Science Society of America, 18 November 2009, http://www.wssa.net/WSSA/PressRoom/WSSA_GlyphosateResistance.pdf
7. “’Superweed’ explosion threatns Monsanto heartlands”, Clea Caulcutt, 19 April 2009, http://www.france24.com/en/20090418-superweed-explosion-threatens-monsanto-heartlands-genetically-modified-US-crops
8. “Paraquat fights glypohsate resistant palmer amaranth”, 30 September 2009,

http://paraquat.com/english/news-and-features/archives/paraquat-fights-glyphosate-resistant-palmer-amaranth
9. Ho MW. Genetic Engineering Dream of Nightmare? The Brave New World of Bad Science and Big Business, Third World Network, Gateway Books, MacMillan, Continuum, Penang, Malaysia, Bath, UK, Dublin, Ireland, New York, USA, 1998, 1999, 2007 (reprint with extended Introduction). http://www.i-sis.org.uk/genet.php
10. Gaines TA, Zhang W, Wan D et al. Gene amplification confers glyphosate resistance in Amaranthus palmeri. PNAS Early Edition 2009, www.pnas.org/cgi/doi/10.1073/pnas.0906649107
11. ARS survey helps growers track two key cotton pests. PHYSORG.com, 1 December 2009, http://www.physorg.com/news178912351.html
12. Ho MW. Farmer suicides and Bt cotton nightmare unfolding in India. Science in Society 45 (in press)
13. Ho MW. Mealy bug plagues Bt cotton in India and Pakistan. Science in Society 45 (in press)
14. Catchot A, Musser F, Gore J, Cook D, Daves D, Lorenz G, Akin S, Studebaker G, Tindall K, Stewart S, Bagwell R, Leonard BR and Jackson R. Midsouth Multtistate Evaluation of Treatment Thresholds for Tarnished Plant Bug. 2009, Mississippi State University Extension Service, http://msucares.com/pubs/publications/images/p2561_pics/bug_1.jpg
15. “Insect control pushes cotton costs higher”, Elton Robinson, Farm Press, 15 January 2010, http://deltafarmpress.com/cotton/cotton-insect-control-0115/
16. Benbrook C. Critical issue report: the seed price premium. The Organic Center. 2009 December. http://www.organic-center.org/reportfiles/Seeds_Final_11-30-09.pdf
17. Godfray HCJ, Beddington JR, Crute IR, Haddad L, Lawrence D, Muir JF, Pretty J, Robinson S, Thomas SM and Toulmin C. Food security: the challenge of feeding 9 billion people. Sciencexpress, 28 January 2010/10.1126/science.1185383
18. Weed Warrior Hebicide-Tolerant Crops, accessed 29 January 2010, http://www.biotechinstitute.org/resources/YWarticles/10.1/10.1.3.pdf
19. Ho MW and Cherry B. Death by multiple poisoning, glyphosate and Roundup. Science in Society 42 , 14, 2009
20. Ho MW. Ban glyphosate herbicides now. Science in Society 43, 34, 2009
21. Cherry B. GM crops increase herbicide use in the United States. Science in Society 45 (in press)
22. Ho MW. Lessons from Bt cotton. ISIS letter to Hilary Benn, UK Secretary of State for the Environment, 4 January 2010, http://www.i-sis.org.uk/lessonsFromBtCotton.php
23. Marketing U.S. organic foods: recent trends from farms to consumers. Carolyn Dimitri and Lydia Oberholtzer, USDA Economic Research Service, September 2009, http://www.ers.usda.gov/Publications/EIB58/
24. Ho MW.UK Food Standards Agency study proves organic food is better. Science in Society 44, 32-33, 2009.
25. Ho MW, Burcher S, Lim LC, et al. Food Futures Now, Organic, Sustainable, Fossil Fuel Free, ISIS and TWN, London, 2008. http://www.i-sis.org.uk/foodFutures.php
26. Delate K and Cambardella CA. Organic production: Agroecosystem performance during transition to certified organic grain production. Agronomy Journal 2004, 96, 1288-98.
27. International Assessment of Agricultural Knowledge, Science and Technology for Development, IAASTD, 2008, http://www.agassessment.org/index.cfm?Page=Press_Materials&ItemID=11
28. Ho MW. “GM-free organic agriculture to feed the world”. Science in Society 38, 14-15, 2008.

Both are beneficial fungi found naturally in soil. Trichoderma are more for cycling nutrients in the soil and providing protection against soil pests (but you will seldom find it labeled as a pest control) while mycorrhizal fungi help more with nutrient and water uptake and increased root growth. Both combined will promote a very healthy root system overall.The two work together well. Trichoderma help make nutrients soluble. Mycorrhizal fungi can actually take the nutrients up and translocate them into the plant.

Q. How do I successfully introduce and propagate mycorrhizal fungi in my hydroponic garden?

Mycorrhizal fungi can be mixed directly with soil-less media or added to the nutrient solution directly just like any regular powder supplement. There is a myth that you cannot use mycorrhizal fungi with synthetic / mineral-based nutrients, but this is not true. Mycorrhizal fungi can be used with soil, hydroponics and cuttings. The key benefits in hydroponics are extended root systems (which naturally lead to an increase in yield), not to mention protection against root zone pests and diseases. Imagine miles of mycorrhizae hyphae exploring the nutrient resources. Mycorrhizal fungi cause roots to branch and form more fine feeder roots that can go after nutrients and minerals.

Q. Should I feed mycorrhizae carbs? (e.g. molasses?)

Molasses and other carbs are good for feeding bacteria and other types of fungi. But you don’t need to feed the mycorrhizae. That’s missing the point. The plant feeds them! It’s the exudates from the plant roots that cause the mycorrhizal propagules to germinate. (There are synthetic compounds that cause the mycorrhizae to germinate but they are unnatural, expensive and not commonly available.) You are better off adding products which contain humic acids (organic growers can use high quality organic inputs such as North Atlantic sea kelp) to promote more root exudates (food for the mycorrhizae).

Q. What hydroponic growth media do mycorrhizae prefer?

Mycorrhizal fungi can create mycelial networks in soil, coco coir, rockwool and many other inert growth media. They can even survive in a totally aqueous environment, as long as it is properly aerated, but they will not replicate. Mycorrhizae will grow and increase in biomass only once they are attached to a plant root.

Q. What about mycorrhizal fungi and high phosphorous levels?

Mycorrhizae fungi spores ‘sleep’ while levels of phosphorus are high (above 70ppm). They only awaken when levels drop lower than this. This is another reason to establish your mycorrhizae as early on in the plant’s development cycle as possible.

Q. What conditions do mycorrhizal fungi prefer?

Temperature: around 68-73°F is ideal but mycorrhizae can also help your plants tolerate occasional temp extremes.

Moisture: mycorrhizal fungi like to have a good air/water mix to thrive. Too moist or too dry is not ideal. Once again, they will help the plant tolerate any extremes that occur.

pH: it depends on the mycorrhizae species but generally they thrive in 5.5-7.5. Some can tolerate acidic conditions better than others while some like alkaline better than others. Look for products that are made from a blend of different species in order to create a healthy mycorrhizae population that will thrive in varying pH conditions.

Q. What conditions should be avoided?

Very high temperatures. (135- 140°F will definitely start killing them off but then, at those temperatures, the happiness of your fungi is the least of your problems!) The less chlorine your water contains, the better for both fungi and plants too. However, typical levels of chlorine from municipal supplies should not cause a problem.

Q. When should I start using mycorrhizal fungi?

As soon as possible! It takes less mycorrhizae to colonize a juvenile plant than a larger one. Commercial growers have negated the cost of mycorrhizal fungi with their increased seed germination rates. It takes a couple of weeks to form on the roots after the first inoculation so get the process started right at the seedling / cutting stage. The trick is to introduce the mycorrhizal fungi spores as early as possible to give them time to establish themselves. This is particularly important if you are growing short-cycle plants.

Q. Do mycorrhizal fungi need to be reintroduced on a regular basis? Do I need to add it more frequently than once with every nutrient change?

Best performance is achieved with numerous applications throughout the growth cycle. You can’t really overdo mycorrhizae. If there are more roots producing more exudates it will probably help to add more mycorrhizae. But don’t bother any later than 2-3 weeks before harvest. It’s a waste of time. Your mycelial network should already be established. It won’t do any harm to keep using it (and often the instructions on the mycorrhizae product will encourage you to!), but you’re just wasting your money! Adding it with every nutrient change won’t do any harm either. It’s just a question of minimizing waste. A good tip is to mix the fungi in a one gallon jug to get it nicely diluted, then pour it into your nutrient solution. Otherwise the powder can sit at the bottom of the res. The white powder you sometimes see at the bottom of your res is just the carrying agent of the spores, not the spores themselves.

Q. What mycorrhizae products can I find in my local grow store?

You’d best ask down at your store! You’ll most likely find a few different brands. The products usually come as a jar of white powder – this is a ‘carrying agent’ for the spores. If you want to compare products, look for the number of mycorrhizal species per pound and the diversity of species. Oh, and the price!

Q. Ok, but how do I actually use mycorrhizal fungi to benefit my plants?

Mycorrhizal application is easy and requires no special equipment. The goal is to create physical contact between the mycorrhizal inoculant and the plant root. Mycorrhizal inoculant can be sprinkled onto roots during transplanting, worked into seed beds, blended into loose growth media, “watered in” via existing irrigation systems, added directly to the nutrient solution, applied as a root dip gel or even probed into the root zone of existing plants. Most hydroponic growers simply add the fungi by diluting the powder holding the spores into some water and adding this to their nutrient solution. It’s very easy.

Q. Do mycorrhizal fungi actually guard the roots against other nasties? If so, which nasties exactly?

Yes. Nasties include: rhizoctonia, fusarium, pythium and phytophthora. They can also mitigate the detrimental effects of high salt conditions.

Q. How exactly do mycorrhizal fungi guard the roots? Do they simply ìcrowd outî the root zone or is it more complex?

Endo mycorrhizal fungi thicken the cell walls around the root cortex making it harder for pathogens to penetrate. They also compete with pathogens for some of the same food sources. Mycorrhizal fungi help with antibiotic production, armoring of roots with chitin, and control of excess nutrients.

Q. What’s the difference between “endo” and “ecto” mycorrhizal fungi?

Endo = has an exchange mechanism inside the root (and hyphae extends outside of the root). Ecto= lives only outside the root. The endo mycorrhizae form with mostly green, leafy plants and most commercially produced plants. Ecto mycorrhizae form with mainly conifers and oaks: more woody plants. Endos are for everything else. In hydroponics, ectos don’t even matter. Fruits, veg, flowers … stuff we love to grow … they love endo.

Q. Are there any differences in how the hydroponic grower should use mycorrhizal fungi compared with the organic grower?

Both types of grower need to get the inoculum near roots. Same product, same application rates. Same number of spores per square foot. Both types of growers can reduce their nitrogen and phosphorus inputs.

Q. Do mycorrhizal fungi help with nutrient extraction in a hydroponic environment or are they more relevant in soil / organics where nutrients need to be broken down first in order to become available?

Mycorrhizal fungi are just as effective in hydroponic applications as they are in organics / soil. A main function of mycorrhizal fungi is phosphorus uptake. It’s important to have a good colonization and a good mycorrhizal fungi “web” already established before you go into flowering.

Fascinated? We are! Be sure to check out “Superfeeding” by Mike Amaranthus and John Eagen for more information on using mycorrhizea to benefit your indoor garden!