AgriGuide

Pest and Disease Management

The role of biodiversity

One of the main pillars of proactive pest management is making farms less attractive to pests. A key requirement for this is to create the greatest possible variety of plant and animal life above and below the ground. This variety of life forms the well-known biodiversity. Biodiversity severely hampers the growth of pests.

The main consequences of improving biodiversity are the following:

Varied plant growth in and around the fields creates a favorable environment for the natural enemies of animal pests (insects and mites in particular). In many cases, these natural enemies keep the pest populations from reaching a harmful level;
Varied plant growth in and around the fields limits the spread of pathogenic fungi, bacteria and viruses, but also the spread of insects and mites;
Varied plant growth in the fields can provide faster-growing and more widespread ground cover, which prevents weeds from germinating and growing;
Multiple crops, which are cultivated at the same time or in rotation, stimulate a rich and varied soil life. This helps control the growth of soil-borne pathogens and weeds;
A varied soil life, created in part by varied plant growth, is also good for the soil structure. Good soil structure and balanced fertilization ensure the optimal growth of crops that have maximum resistance to diseases and animal pests and that can compete successfully with weeds.

The measures listed above not only help control pests, but often have other positive effects as well, which is all the more reason to implement them. Additional advantages can include the following:

Ground cover crops protect the soil from intense sunshine, avoiding evapo-transpiration;
Keeping the ground covered with plants prevents soil erosion, caused by heavy rains or strong winds. This is particularly important on hilly terrain;
Combining leguminous crops with other crops allows both to profit from the nitrogen fixation of the leguminous crops;
Combining a shallow-rooted crop with a deeper-rooted crop makes better use of the applied manure or fertilizers;
A well-balanced crop rotation also ensures that the fertilizer applications incorporated in the planting schedule are optimally utilized.

Improving biodiversity

Plant growth alongside fields and ditches

Vegetation borders along the edges of fields and ditches can serve to ward off pests arriving from elsewhere. A combination of tall-growing trees and bushes with an undergrowth of grasses and herbs is sufficient for this purpose. As pests are carried by the wind, it is important to plant borders along the edges of the fields to face the prevailing winds. Many natural enemies of insects depend for part of their life cycle on nectar and pollen. It is therefore also important to plant on the borders trees, bushes and herbs rich in flowers.

However, vegetation may also offer food and shelter for some crop pests; farmers may need to adapt it to make it more attractive to the natural enemies and less attractive to pests.

It is best to use plant species that grow well under local conditions. A permanent border composed of a mixture of grass seeds with annual and perennial herbs can be made. The border has to be maintained by cutting once or twice a year for the first two to three years, primarily to suppress the growth of undesirable plants. It is not advisable to fertilize the border because that would stimulate the growth of grasses, which would eventually take over. Herbs and spices are encouraged but weeding is required in the early growth stages, to avoid nutrients competition.

The push-pull effect protects maize from Stem borers and Striga

Stem borers (caterpillars of moths) are the major insect pests of cereal crops in eastern and southern Africa. Losses can reach as high as 80%, while those due to Striga range from 30 to 100% in most areas.

Researchers found a way to grow maize together with two other crops. One attracts stem borers. This is the “pull effect”. The other intercrop repels the stem borers, causing the push effect. Together they effectively protect the maize crop from stem borers.

Both domestic and wild grasses can cause the pull effect. Napier grass is the most effective. It is planted in the border around the maize fields where invading adult moths are attracted to it. Instead of landing on the maize plants, insects are attracted to what appears to be a tastier meal. Napier grass has a particularly clever way of defending itself against the pest onslaught: once attacked by a borer larva, it secretes a sticky substance that physically traps the pest and effectively limits its damage. And so the natural enemies lurking among the grasses go into action.

The legume Desmodium repels stem borer moths and ‘pushes’ them away from the main crop (maize or sorghum). Desmodium is planted in between the rows of maize or sorghum. Being a low-growing plant, it does not interfere with the crops' growth and has the further advantage of maintaining soil stability and improving soil fertility through nitrogen fixation. It also serves as a highly nutritious animal feed. Other legumes have this effect as well, but Desmodium also effectively suppresses Striga.

Crop rotation

Crop rotation means that various crops are cultivated in successive planting seasons. Crop rotation plays an important role for soil fertility, but also for controlling various pests such as soil-borne diseases and perennial weeds. Ideally, farmers should rotate grain crops with vegetables and root crops.

Be careful not to grow two crops from the same family one right after the other, such as potato and tomato, or celery and carrot. It is possible, however, to grow a grain crop more frequently than others in a rotation, because soil-borne diseases do not thrive in grain crops. Regular food and cash crops have to be taken into consideration when planning a rotation.

Organic farmers in Benin successfully grow cotton without pesticides

Cotton attracts a large number of insect pest species. That is why conventional cotton growing is associated with intensive spraying with insecticides. Benin cotton farmers, associated in the NGO OBEPAB (Organisation Béninoise pour la Promotion de l’Agriculture Biologique) switched to a system of organic cotton production. No synthetic pesticides and no inorganic fertilizers are used. Another difference with conventional farming is that crop residues are recycled instead of burnt, to increase soil fertility.

Additional advantages are that organic farmers do not need to buy pesticides, and farmers get a better price for their cotton.

The basis for organic cotton is a three year crop rotation. The cotton crop in the first year is fertilized with cottonseed press cake and is grown on ridges of decomposing crop residues on the contour line. The cotton crop is followed by grain (maize, millet, sorghum) and oil plants (peanuts, sesame or safflower).

Other possibilities include spices and vegetables like chilli or onion. In the third year, pulses like pigeon pea, mung bean, chick pea and cowpea are grown. The following cotton crop (in year 4) profits from the nitrogen provided.

In longer periods between two growing seasons, the soil is not left bare, but cover crops are grown instead, to prevent soil erosion, to suppress weeds and to supply food and shelter for beneficial insects that control cotton pest insects.

Popular cover crops include alfalfa, sweet clover, red clover, white clover, vetch, cowpea, buckwheat and mustard. In addition, trap crops are grown on the edges of cotton fields. They attract pest insects from the cotton crop. Trap crops include sunflower, cowpea, alfalfa, okra and early sown cotton.