Sustainable Agriculture Extension Manual

Controlling crop pests and diseases

Methods of controlling pests and diseases in sustainable agriculture are sometimes very different from conventional measures. In many cases, our knowledge of natural pest control has been handed down in the form of old farming traditions whose value is no longer recognized. One of the aims of sustainable agriculture is to rediscover and further develop this knowledge and to give the farmers the opportunity to fall back on methods whose cost and ecological side-effects are minimal.

Sustainable agriculture aims to reduce the incidence of pests and diseases to such a degree that they do not seriously damage the farmer's crops—but without upsetting the balance of nature. Use cultural control methods to prevent pest and disease attack. If these do not work, there are several natural pesticides that can be used to control an outbreak.

Preventing pest and disease outbreaks

Plough after harvest

Many pests breed or develop in the residue of the previous crop. If you plough the stubble under after harvesting, you can control these pests.

Choose resistant varieties

Select crop varieties that are resistant to the main pests and diseases in your area. Scientists have developed high-yielding varieties that are resistant to important pests and diseases, though many local varieties are more resistant than modern varieties.

Plant several different crops and varieties

If you plant all one crop or variety, it may be completely wiped out by a pest attack. But if you have planted several crops, or several varieties of the same crop, chances are that at least some will survive an attack.

Rotate crops

If you plant the same crop on the same piece of land year after year, the pests, diseases and weeds that attack that crop may multiply. Instead, try to grow a different crop each season: for example, plant beans in a field where you planted maize the previous season. This will reduce the number of pests and diseases, since most do not attack different types of crops.

Use healthy seeds

Some diseases can be carried by the seeds. Choose seed only from healthy plants, or buy seed from a trusted source.

Plant at the right time

Often this means planting early, to avoid the time when there are most pests and diseases.

Minimize water stress

Water stress weakens a plant's ability to resist attacks by pests. Cultural methods that minimize loss of water from soil and the crop include establishing windbreaks, adding sufficient organic material to the soil, mulching (where practical and where this will not attract termites), and planting at the appropriate time. If possible, provide irrigation water, especially for high-value crops.

Maintain beneficial insects and insect-eating birds

Keep a variety of plants around the farm as habitat for insect-eating birds and beneficial insects (insects such as ladybirds and wasps that feed on pests like aphids and cabbage worms). Avoid using synthetic chemical pesticides, because these kill off these beneficial insects.

Plant trees or hedges as windbreaks

Apart from breaking the wind, trees and shrubs moderate the temperature, reduce evaporation, and provide a habitat and food for useful insects. Tall trees, such as Grevillea robusta, and trees of medium height, such as sesbania (Sesbania sesban) or leucaena (Leucaena leucocephala) provide good habitat and wind protection. Include plants such as tithonia (Tithonia diversifolia) in the hedge. It has not yet been scientifically proven that tithonia repels pests, but very clear positive effects have been observed. Tithonia can also be used as green manure and to produce liquid fertilizer (see the sections on Using organic matter and Manure tea).

Plant diversion crops

Such crops as sunflowers and finger millet, and also local plants which bloom and bear fruit, attract birds and insects. You can take advantage of this by growing such plants at the edge of your fields. These "diversion crops" attract the pests away from the main crop.

Plant insect-repellent crops

Plant flowers like marigold and certain kinds of vegetables which help to control pests in or around the main crop. This is sometimes called "companion planting". Plants with strong smells, such as French marigold and coriander, act as repellents and can protect the crops nearby.

Apply organic matter

The use of compost, mulch, and green manure crops can have a very positive effect against the development or pests and disease.

Controlling pest outbreaks

Sometimes an outbreak of a pest cannot be avoided. At these times the farmer may be forced to interfere in the natural cycle to prevent crops from being destroyed. This can be done in various ways.

Hand-picking

Large insects should be collected by hand. Of course, this is possible only if the number of pests is not yet too great, and they have not become too widespread on the crops. If the danger is recognized early enough, extensive pest damage can be avoided through simple hand-picking.

Synthetic pesticides

If hand-picking is not sufficient or practical, it becomes necessary to resort to some kind of chemical control—using botanical or synthetic pesticides. Many synthetic pesticides are very difficult for nature to break down and have negative side-effects on human health when improperly handled. Only in rare cases are they selective in their effects. They should only be used as a last resort when a pest outbreak threatens to wipe out a farmer's entire crop, or for selective spot-control of difficult pests or diseases, to keep them from spreading.

Botanical insect repellents

Among these are Mexican marigold (Tagetes minuta), chilli (Capsicum annuum) and Ocimum suave. Made into solutions that can be sprayed or watered with, these can prevent or reduce the attacks of various insects and diseases. Repellents also play an important role in storing crops after the harvest. Ashes, sawdust and the leaves or fruit of many different plants can be mixed with the produce (see the section below on neem) and protect it from disease and pests during storage.

Moderate killers

Pyrethrum and chinaberry (Melia azederach) are among the moderate killers, a group of botanical pesticides whose level of effectiveness is relatively low.

Preparing botanical pesticides

All of the pesticides mentioned below should always only be used alone and only when the plants show the symptoms of an attack. Do not use them as a preventive measure (the cultural control measures described above should be used for this).

Repellents

Fill 2/3 of a small container with the cut-up leaves and flowers of Mexican marigolds and Ocimum suave, or the fruit of chilli peppers. Then fill the rest of the container with clean water. Cover the mixture and let it stand for 5-7 days. Then filter the contents and add 30 g of soft soap for every 5 litres of water. Use diluted. For young plants, you can dilute one part of the solution with five parts of water. For older plants, dilute one part of solution with an equal amount of water.

Mexican marigolds generally work as a repellent for smaller insects and nematodes. Chillies offer very effective protection from the common cutworm and larger insects. Ocimum suave can be used against all insects.

Pyrethrum

Boil two cups of pyrethrum flowers in 5 litres of water. Allow to cool, then filter the liquid and dilute it with twice to five times as much clean water. Add 30 g of soft soap in every 5 litres, then spray the liquid.

Tobacco

Boil a cup of cigarette butts (or 250 g of tobacco) in 4 litres of water. Allow the liquid to cool, filter it, and dilute it with the same quantity of clean water. Then mix with 30 g of soft soap in every 5 litres of liquid before spraying it. This tobacco solution is very toxic and should be used only in an emergency. It is effective against maize stalkborers, lice, mites, worms, caterpillars and many other pests.

Neem

The neem tree (Azadirachta indica) is widely distributed in coastal regions of East Africa and the eastern drylands of Ethiopia. It was introduced from its home in South Asia, where it highly appreciated for its medicinal and pest-repelling properties.

The neem tree is often confused with the chinaberry (Melia azaderach), a closely related species with very similar leaves. But there are two easy ways to distinguish the two. First, the fruits of neem drop off when they are ripe, but the fruits of

chinaberry remain on the tree. Second, neem bark is rough, but that of chinaberry is smooth, and of a darker colour.

How to make neem powder

1. Collect only ripe neem fruits (or berries), which are yellow, not green. Collecting a good quantity of berries is easy, as a mature tree (10 years old) will produce 30-50 kg of berries each season. Remove the outer layer of pulp if birds have not already done this.

2. After cleaning the seeds, spread them out in the shade on mats to dry for a few days. Make sure they are not exposed to rain or direct sunshine. The active ingredients in the seeds (the main one is called "azadirachtin", after the Latin name for the tree) will lose strength when exposed to high heat and sunlight. An open, breezy place in the shade of a tree or house is best for drying. Attention! The seeds must be well dried before storing them to avoid the growth of moulds which will quickly spoil the seeds, and your efforts!

3. Store the seeds in well-aerated baskets or jute gunny sacks. Do not put them in plastic bags. These will keep moisture inside and make the seeds rot.

4. Remove the seed coat. For this you need a large mortar, which you do not use for grinding other cereals. Neem is very bitter, and will give an unpleasant flavour to anything else you grind in the mortar. Place about 0.5 kg of the seed in the mortar and pound it very gently—not hard enough to crush the seeds, just enough to break off the seed coat, exposing the kernel inside.

5. Next, separate the broken seed coats from the kernel by winnowing them in a light wind.

6. Put a few handfuls of clean neem kernels into the mortar and—this time—pound vigorously until you produce a fine powder. Make only as much powder as you will use in a few weeks, since the insect-repelling properties will not last as long once you make a powder, especially if it is exposed to light or heat.

Controlling moles with stinging nettles Not only insects can be controlled with plant-based methods. Moles are a serious pest in many areas, particularly those with higher rainfall. They can be controlled with various poisons and synthetic chemicals, but these are costly and can be dangerous to handle. A farmer in Kenya has found a way to control moles using the leaves of the stinging nettle plant (Obetia radula), known in some areas as hila hila or thabai. Other plants with spiny leaves or stems can also be used. Moles do not like the nettles as they irritate their sensitive skin. They move somewhere else, where they may be eaten by predators. Dig out a molehill so you can see the tunnels leading to it on both sides. Use a cloth or gloves, push pieces of stinging nettle as far as you can into the tunnels. Cover the tunnel with soil. Repeat for as many tunnels as you can find.

How to use neem powder

Neem powder is very effective for protecting crops from a wide range of pests. Note: neem does not kill pests immediately, as do many synthetic pesticides. Do not expect to see insects fall dead when using neem! When bugs feed on plants with a coating of neem solution, they will quickly stop eating, and will also stop growing and reproducing.

On vegetable crops. Mix 500 g (3 handfuls) of neem powder with 10 litres of soapy water. The soap helps dissolve active substances in the neem powder, and makes them stick to the plant. Allow this mixture to sit overnight. After stirring it well, spray the solution onto the plants, or sprinkle it onto them with a grass broom. If you use a sprayer, be sure to sieve the solution first using a fine cloth to avoid clogging the spray nozzle. When applying the solution, take care to cover the leaves of the plant completely, especially the undersides, where the pests like to hide. If pest infestation is heavy, apply twice in one week. Otherwise, one treatment every 7 to 10 days will do. Stop using the neem solution 3-4 days before harvest to keep your cabbages from having a neem flavour (washing the produce well will remove this taste, but takes more water and time).

On cereal crops (maize, sorghum, millet). One particular pest—the stalk borer—can be readily controlled using neem powder. Mix equal parts of the powder with sawdust or termite clay. Put a pinch of this mixture into the funnel formed by the young leaves. When it rains, the active substance will be carried down to where the borer hides and will stop it from doing any damage. Apply the