When using crop-rotation, the insects will not find their host plant above the soil. Disease prevention: Just like insects, plant diseases can also over winter in plant leaves and vines under the soil. The farmers can also help guard against this by removing and destroying any diseased plants. •Trap cropping Trap cropping is the planting of a trap crop to protect the main crop from a certain pest. The trap crop can be from the same or different family group, as the main crop, as long as it is more attractive to the pest. There are two types of planting the trap crops; perimeter trap cropping and row intercropping. Perimeter trap cropping (border trap cropping) is completely surrounding the main crop with the trap crop. It prevents a pest attack that comes from all sides of the field. It works best on pests that are found near the borderline of the farm. Row intercropping is the planting of the trap crop in alternating rows within the main crop. The principle of trap cropping rests on the fact that virtually all pests show a distinct preference to certain plant species, cultivars, or a certain crop stage. Manipulations of the stands in time and space so that attractive host plants are offered at the critical time in the pests and the crop’s phenology leads to the concentration of the pests at the desired site, the trap crop. Techniques of manipulation range from establishing an early or a late trap crop of the same cultivar as main crop to panting a completely different plant species (Hokkanen, 1991). Farmers are motivated to utilize trap cropping because of the difficulties in coping with the pest situation in other ways. Sometimes the cost of chemical pesticides and the number of treatments required are high, therefore more economical ways have to be developed (Swezey & Daxl, 1988). Additionally, the pests have often evolved resistance to commonly used pesticides (Swezey & Salamanca, 1987), which requires some alternative control strategies. In some cases, no effective chemical pesticides are available. 30
Practices on use and application of pesticides in Armenia Besides its potential role in improving the environmental health and overall performance of conventional agriculture, trap cropping techniques may have special importance to subsistence farming in the developing countries such as China and India. Additionally, the increasing sector of organic farming also could exploit this strategy of pest control (Hokkanen, 1991). Another function of trap crops is their use for attracting natural enemies of pest insects to the fields and concentrating them there to enhance naturally occurring biological control. •Intercropping Intercropping is the cultivation of two or more crops simultaneously on the same field. It also means the growing of two or more crops on the same field with the planting of the second crop after the first one has completed its development. The rationale behind intercropping is that the different crops planted are unlikely to share the same insect pests and disease-causing pathogens and to conserve the soil.