Insect pests and plant diseases are among the main factors limiting bean production in Tanzania. A survey of methods of pest and disease management in small-scale bean production systems was carried out in Mgeta Division.
The results revealed that small-scale farmers are well informed of the major insect pests limiting bean production. The farmers know the type of damage caused by most insect species and the time of their occurrence. Although farmers are not aware of the pathogens affecting their crops, they can distinguish damage caused by insects from those due to diseases. Farmers are also aware that diseases are associated with environmental factors which influence disease development.
Farmers use both deliberate practices and incidental practices to manage insect pests and diseases.
The most frequently used deliberate practice is avoidance. Choice of growing season and date of planting are observed closely as a means of avoiding diseases. Although beans are cultivated in both growing seasons (September–December and February–May), the first season is the best for growing beans. Rains are not very heavy, but reliable and well distributed, and the season does not end up with low temperatures and high humidity which favour development of fungal diseases. Planting commences as soon as the rains start because early planted crops suffer less from pests. Farmers do not use purchased inputs in the form of fertilizer and pesticides. Larger insects are killed mechanically.
Incidental control takes place in the form of a number of cultural practices. Intercropping with maize, potatoes, cowpeas, pigeon peas, cassava or sorghum is normal and reduces the risk of crop failure. Terracing, where crop residues and weeds are buried under soil, reduces the amount of initial inoculum of certain pathogens. Farmers use a mixture of seeds of different cultivars deliberately, some high yielding and early maturing; and some late maturing, thus ensuring the farmer of food early in the season and beans as a cash crop later. Such variety mixtures appear to provide a buffer against pests and diseases.
A breeding strategy should be developed for variety mixtures instead of pure line varieties as the productivity of pure varieties in most cases is associated with the use of purchased inputs such as fertilizers and pesticides which are beyond the reach of small-scale farmers. Variety mixtures have a greater efficiency in using environmental resources, and are less affected by pests and diseases, and thus give higher yields than pure varieties.