HOME GARDEN TECHNOLOGY LEAFLET 10

SAFE AND EFFECTIVE CROP PROTECTION

WHAT ARE PESTS AND DISEASES?

Good home garden managers know how to manage pests and diseases, they understand what pests and diseases are and, more important, recognize what kind of pest or disease is causing a given problem. Here are some simple points to remember:

• Pests and diseases are living things (insects, fungi and bacteria). Generally, they cannot survive for long without a place to live, such as plants or dead plant parts.
• Insects can sometimes be seen on plants or in the soil. They damage plants mostly by chewing holes in roots, leaves and fruit or by sucking sap out of the leaves, stems and fruit. Not all insects are pests. Bees, for example, pollinate flowers so that crops have fruit and seeds. Also there are beneficial spiders and insects that eat pests and should be protected.
• Fungi are quite small and they attack all parts of a plant. Signs of fungi may be a powdery substance under leaves; rotten patches; black spots on stems, leaves and fruit; or wilting because of rotten roots. Fungi may spread through rain splashed up from soil on to plants, or they may be carried by the wind from one plant to another.
• Bacteria and viruses are visible only with a microscope. They may cause rot in a plant's roots and stem, oozing sap, distorted or striped leaves, black spots or other symptoms. They are spread by insects, water, soil, affected plants and plant materials such as seeds and tubers.

GOOD FARMING PRACTICES PREVENT PROBLEMS

There are important and simple ways to help plants stay healthy and productive.

Grow plants where soil, water and light conditions suit them. Papaya needs full sunlight; coffee needs shade. Taro likes wet soil while papaya might get root rot in wet soil and die. It is important to select the correct plant for each place in the garden.

Feed your crops and they will feed you. Yellow leaves, poor growth and small fruit are often the result of lack of water or nutrients in the soil. As long as a plant is sited correctly and no pests or fungi can be seen under its leaves, the application of fertilizer or manure may improve the plant's growth.

Minimize competition. Plant crops with just enough space for each plant to grow to its full size. Weeds sometimes grow faster than crops and take soil nutrients necessary for crop growth. Weeds should be removed before a crop is planted. Mulch placed between plants can prevent weeds from taking root until the crop is well established and covers the soil.

TABLE 1
Common pests and diseases in African home gardens

Protect plants from strong winds, seasonal dry winds and salty winds from the sea. Wind can reduce plant growth and damage leaves and flowers. Use multipurpose trees as living fences (see also Home Garden Technology Leaflet 11, "Living fences").

Avoid planting large areas with a single crop (monocropping). Intercropping is a useful technique for increasing the number of crops in one place and preventing the spread of disease. If one plant develops a disease, it can spread rapidly throughout the whole crop, unless there is another crop to act as a barrier.

Use trellises. To keep fungi away from vine crops such as pumpkin, grow the plants on a trellis. For more details, read Home Garden Technology Leaflet 13, "Multilayer cropping". If the soil is extremely wet or has a lot of clay in it, grow plants above the soil in baskets or in containers filled with good soil and compost.

PHYSICAL CONTROL METHODS

The safest way to avoid pests and diseases is by practising good garden hygiene. Remove and burn diseased plants before the disease can spread. Remove and burn or compost dead branches, fallen fruit and tall, dense weeds which can house pests and diseases. Keep the compost heap away from growing vegetables. Do not replant the same crop in the same place; plant a different kind of crop instead. Read more about this in Home Garden Technology Leaflets 12, "Multiple cropping", and 15, "Intensive vegetable plots".

NATURAL PESTICIDES AND DETERRENTS

Many household items can deter insects. Sprinkle ash over sucking insects, such as aphids, which can be found on the undersides of leaves. Ash sprinkled around the base of a plant can deter some crawling insects. Soapy water poured or sprayed over sucking insects also can be effective. Slugs and other pests can be trapped in a half-buried bottle containing a little beer.

Soak coffee grounds or tea leaves in water and then spray on plants to deter insects. Furthermore, plants such as marigold, lantana, garlic, chilli, lemon grass, and basil, among others, repel insects. Farmers plant these as companions to food crops because in some cases their smell acts as a repellent; in other cases the scent (i.e. marigold and basil) attracts insects thus preventing these from feeding on food plants. Garlic acts through its roots, which release fungicidal chemicals into the soil, thus helping to control soil-borne diseases. Diluted cow or goat urine sprayed on crops not only repels many insects but also prevents animals from feeding on those crops.

Some farmers know how to prepare natural pesticides by mixing the extracts of certain plants, seeds or fruits with water and spraying the solution on to crops. In general, a home garden manager must experiment to find effective, easy-to-prepare solutions. Do not forget, however, that some natural pesticides are poisonous to animals and humans. Follow the same safety rules as with chemical pesticides.

Table 2 lists some of the insecticidal plants found in different parts of Africa that are used by home garden managers.

TABLE 2
Examples of insecticidal plants

The following are examples of how to prepare natural pesticides. There may be many more that are used in a given community. The local agricultural extension worker or a neighbour can suggest what other natural pesticides are known to work well locally.

Chillies mixed with garlic or onion residue

To control aphids, shred a handful of dried chillies (about 10 g) and some onion or garlic and mix them together in about 1 litre of water. Leave the mixture overnight, then strain the concentrate through a cloth and dilute it in 4 to 5 litres of water. Brush or sprinkle it on the affected plants. If the mixture is too strong, it will burn the plants' leaves. It is better, therefore, to use a lower concentration and repeat the treatment. Avoid bright sunlight during application and do not let the solution come into contact with human skin or eyes, as it is a strong irritant.

Neem and Persian lilac

Seed powder from neem or Persian lilac is extremely effective against pests that are a menace during food storage. The powder is obtained from dried, crushed and ground seeds. One part powder should be used for 50 parts stored food.

To make the powder, crush the seeds using a mortar and pestle to remove the outer husk. Then crush the kernels in the mortar until a brown, slightly sticky mass is formed. Add a little water to make a paste. Knead and squeeze the paste to press out the oil.

About 1 cup of oil can be produced from 1 kg of hand-pressed kernels. This is only about half the amount than can be extracted by using a mechanical press. After hand pressing, the remaining oil cake still has insecticide properties and can be applied to growing crops to control several pests that live in the soil, especially nematodes.

Pyrethrum

Pyrethrum originated in southern Europe but now thrives in subtropical highlands. Its active ingredient is concentrated in its flowers. These are dried and ground into a powder that is then applied by dusting or is mixed with kerosene and sprayed, brushed or "flicked" on (this can be done with a maize husk or grasses). Since pyrethrum is sensitive to sunlight and its effectiveness is quickly reduced if it is applied in bright sunlight, apply it towards sunset. The application may have to be repeated if the infestation level is high.

REDUCING THE RISK OF POISONING WHEN USING CHEMICAL PESTICIDES

Occasionally, the use of chemical pesticides is the most effective method of pest and disease control. Many different pesticides are widely available. They are expensive, however, and may be ineffective and dangerous if used incorrectly. Always read the label on pesticide packages and respect the following rules for their safe and effective use.

Identify targets. Many pesticides are effective only against specific pests or diseases. Before selecting a pesticide, identify the pest or disease causing the problem.

Protect yourself. When handling pesticides - especially when mixing or spraying them -it is important not to let the chemical touch the body. If it does, wash it off immediately. Gloves or plastic bags should be worn over hands, and a breathing mask or a cloth should be used as an air filter. Wear a hat and a long-sleeved shirt or jacket. Pesticides can be absorbed through the skin easily. Be careful, also, when hand-washing clothes used during spraying, since pesticides can be absorbed during washing.

Mix correctly. Follow the instructions on the label to mix the chemical to the right concentration. Do not add more or less than the amount specified as this may reduce the chemical's effectiveness. Repeat applications only according to the frequency written on the label.

Respect the withholding period. After any pesticide is applied to a crop, a certain amount of time must pass before that crop can be harvested and eaten or sent to market. This is known as the withholding period. For some pesticides this period is only one day. For others it may be as long as two weeks. If a crop is eaten without waiting the recommended time period, poisoning may occur. If children or animals cannot be kept away from the crop, do not use the pesticide.

Practise safe storage and disposal. Keep pesticides safely locked away from children to avoid accidental poisoning. If pouring out pesticide that remains in a tank after spraying, stay a safe distance from streams and ponds to avoid poisoning the water or fish.

If in doubt. Never use a pesticide if you are not sure of the procedures.