Hydroponics Made Easy
CHAPTER 8 PEST AND DISEASE DI SEASE MANAGEMENT The common conception is that plants grown indoors or undercover in places such as in the house, in a greenhouse, or under cover, will have less problems with pests but in fact the reverse of this is the case. The main conditions that cause plants to thrive are equally appreciated by most pests. Warmth, protection from winds and frosts, humidity, moisture, light and freedom from predators are all conditions that encourage pest populations to reach explosive proportions. Plants grown outdoors do not have such favourable conditions, but they also have the full range of natural pest predators such as birds, bugs and other insect insect predators to control pest populations. populations. This is not to say that the outdoors is the preferred location for your hydroponic system. It’s not. The message is that you need to be aware of the pest problems that can develop and of the means at your disposal to recognise and to control them.
Quarantine Most of the pests and diseases that affect crops are imported with planting materials. Once they are in they are hard to get rid of, even in a small greenhouse. Everytime you introduce a new plant to the greenhouse you run the risk of introducing new pests and diseases. You can reduce this risk by practising strict quarantine on all new plants. Treat all new material with pesticides and fun gicides before introducing to the greenhouse. Hence, it is safer it to raise your own seedlings.
The concept of pest control Be very aware that pest control is just that. Control of pests. Not extermination. Not eradication. Simply keeping the pest problem to such manageable manageable proportion as to not seriously affect the production of your plants. To keep pests limited to a population which will keep the damage to your crop at an insignificant level.
Common problem pests The most common pests you are likely to find indoors or under cover are Aphids, White flies, Red spider mite, Caterpillars, grubs and the like, and Snails.
How to control pest indoors There is a relatively limited range of options available to you. Limited range but not necessarily limited effect. About the only practical, effective way for you to control pests is by spraying. The range of possi bilities that come come under the general general heading of insecticides insecticides is considerconsiderable. We feel though that the t he minimum interference with nature is the preferred option. That frequent, frequent, regular applications applications of natural and en 1
Attach Vecro strips here here
Slugs and snails are not a problem if the growing containers are above ground. All you need is to attach a strip of Velcro around every support.
Hydroponics Made Easy
environmentally friendly spray solutions is far preferable to applications of some of the t he very effective but strong and sometimes dangerous chemicals that are available to you. This takes on even more meaning if the plants you are growing are crops to be eaten.
Examples of safe pesticides.
Soapy water, especially a mix of Clensel and water is a good option. As is the natural and organic pest control agent of Pyrethrum and various other organic pest control preparations. Our preferred preparation is a mixture of pyrethrum, Clensel and water. Companion plants work well too. A dwarf variety of Marigold in each pot as well as the main plant will repel aphids. aphids.
The essentials of Spraying First thing needed is a good quality sprayer. A few extra dollars that may be needed to get a good one will be quickly repaid by minimising losses. Two main types of good quality sprayers are available. The pump and pressure pressure pot type of hand sprayer, sprayer, and various types of backback pack sprayers, including even backpacks with rechargeable rechargeable battery powered motorised motorised drives that make make spraying very very easy.
Clensel – a soap solution designed to suffocate pests such as aphids.
The qualities that you are looking for in either type of sprayer are their ease of use and handling, their ability to contain a reasonable supply of spray and the two most important qualities of being able to supply a high pressure spray and a nice fine mist that gives good coverage of the plant. The best policy is to spray for pests once a week right from the time you plant and regardless of whether you see a pest problem or not.
Neem Oil – natural extracts from Neem trees.
Very often by the time it is obvious that you have a pest problem, the problem is out of control. control. Make sure you give each plant and every part of the plant a light but comprehensive coverage of fine mist spray. Pay attention to the stems and the under side of the leaves. Make sure that you use a breathing mask, preferable the agricultural type with a replaceable canister cartridge. Note that the cartridge will gradually lose its filtering efficiency to the point that six months after you have removed it from its original sealed packet, it loses its filtering ability regardless of whether or not it has actually been used. It is best to spray when there is little or no wind outside even though you are spraying indoors. Mornings and sometimes evenings are times when the wind is often at its gentlest. On the week before or the t he week after you give the regular boosted dose, it is also a good management technique to add a little of a com pound called Rogor Rogor 40, another insecticide insecticide and one one that is stronger and consequently consequently a little more toxic. This is because insect pests have an uncanny ability to become immune to any regularly used insecticide. Varying the dose and the composition of the spray keeps them con2
Garlic/chilli sprays.
Sticky insect traps.
Hydroponics Made Easy
confused. Even a change of brand of the substance you are using seems to have an effect. Before you bring new plants into your regular growing environment, it is good practise to spray them or even to soak them in a pyrethrum solution. Some pests, particularly the sucking types of pest such as aphids and white flies can transmit viruses such as those that affect capsicums and similar plants. Controlling pests is also minimising the chance of spread of disease.
Natural Biological Control Nowadays, quite a number of troublesome pests can be controlled by biological methods. A good example is the use of predatory mites for the control of two-spotted mite, a very difficult pest to control by spraying.
And a couple of oddball but effective solutions. Sticky substances like flypaper and strips of double sided tape can be useful addition to your spraying regime for the control of white flies but on its own is not enough. And snails can be kept from their dinner table if it is on legs and you apply bands of Velcro to all the legs. Snails and Velcro it seems, do not mix.
Disease management Hydroponic growers have relatively little to fear from diseases, but little does not mean nothing. The species family called Cucurbits which comprises plants such as Cucumbers, zucchinis, pumpkins and the like are among those plants that are a little littl e more prone to diseases. Also eggplants, and tomatoes.
Root Disease
An orange Predatory Mite (left) about to pounce on a Two Spotted Mite. Actual size 0.55mm.
Predatory Mites are now widely used for the control of spider mites.
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Is not common in hydroponically grown and well managed plants. However, the plant that is the most susceptible, is probably the most common crop plant, the tomato.
Predatory Predatory Mites are absolutely safe to plants and humans.
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Predators hunt out twospotted mites in dense foliage and hard to spray places.
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Leaf Disease Is mainly confined to the leaf surface areas in the form of mould or powdery mildew. mildew.
Fruit Disease The main type that you would occasionally encounter, if at all, is blossom end rot.
Disease Control There are a number of active measures you can take to keep your crop disease free including spraying of various anti viral, fungal and bacterial compounds, but spraying should be kept as a last resort. Sanitation, Environmental control and cultivation of disease resistant varieties should be considered your first line of defence. Keep all dead and decaying vegetable matter out of the area. Keep the area as free from humidity and as dry as possible. Plant disease resistant varieties wherever possible.confused. possible.confused. Even a change of brand of the substance you are using seems to have an effect. 3
Hydroponics Made Easy
Types of Diseases The three main types of plant disease are 1. Viral 2. Fungal 3. Bacterial Their mitigation and control should be only a minor consideration to you, but a very short description of what they are, how to recognise them and the appropriate treatment treatment is worth detailing here. VIRAL DISEASES: DISEASES: The recognisable signs are deformation of the leaves, especially on the growing tips. These are signs that are also caused by the infestation of sucking insects such as aphids and the main treatment is to control these insects. Viral diseases can also be carried over from one generation of plant to the next being present in the seed. This is more prevalent in developing countries where there is no effective control on seed production. In most areas if insects are controlled controlled so too will be the virus problem, problem, especially if virus free seeds or seedlings are used. FUNGAL DISEASES: White powdery mildew on leaves will be the main visible indication of fungal disease. Fungal diseases favour an environment that is warm and humid and they are particularly partial to zucchinis, pumpkins, cucumbers and such vegeta bles. The best methods of control come from initially planting fungal resistant varieties, keeping good ventilation, keeping the atmos phere as dry as possible and by avoiding overhead watering, particularly with fine sprays. When you think that fungal diseases might be a problem or if you have experienced problems in the past, spraying a fungicide may be the answer. If you do this, spraying at the minimum concentration on a regular preventative schedule is recommended. BACTERIAL BACTERIAL DISEASES: This is a problem that you are not likely to encounter except in the case of tomatoes that have been raised in a soil environment from seed to seedling stage and will be present in the root system. This will normally only occur in warm climate areas. You will probably not find the cause of the problem until it is too late and the problem can mostly be avoided by growing your own seedlings from seed in a sterile environment such as a cube of growool or in perlite. If unsure, use a grafted tomato which has a rootstock that is resistant to root disease. •
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Use Disease Resistant Varieties. Some varieties are less susceptible than others to diseases. For example, the special cucumber hybrid shown below is less prone to powdery milder attack than the local varieties.
Environmental Control. Good environmental controls will reduce the incidence of disease.
Air movement . Good ventilation in a greenhouse and induced air movement with a fan can minimize the incidence of diseases, particularly powdery mildew. Lowering Humidity. High humidity encourages the proliferation of disease. Autopot Systems, unlike overhead watering, will not increase the humidity in the greenhouse.
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With cucumbers, it is far more rewarding to grow varieties like the Pipinex Hydbrid (continental variety) and Hylaris Hybrid (smaller variety). Reasons:– - they are more resistant to powdery mildew disease - they bear only female flowers which will form fruits without fertilization. Hence, they are seedless. - they are high yielding and - are also burpless.
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