Foliage beetles (Ootheca spp.; Monolepta spp.)
In East Africa foliage beetles (Ootheca spp.; Monolepta spp.) are commonly found feeding on bean leaves. Foliage beetles chew small round holes in the leaves. They are about 4-7mm long. They may be a serious problem when present in large numbers or when attacking young plants. Heavy attacks may cause defoliation. Attack on young plants may reduce plant vigour, plant size and yield. The problem is more acute in fields with continuous growing of beans.
Ootheca beetles are normally not serious pest of French beans, but are an important pest of common beans in East Africa. The larvae (grubs) of foliage beetles live in the soil feeding on roots. Their feeding may cause stunted growth and premature ageing of the plants.
Grubs of weevils live in the soil feeding on roots or may bore into the stem of the bean plant causing swellings or galls, as is the case of the striped bean weevil. Plants attacked by grubs of this weevil show stunted growth and may die. The stem of the plant breaks easily during harvesting (see more below).
- Practice post harvest tillage to expose the grubs in the soil to the sun heat and to predators.
- Rotate beans with non-host plants such as maize or sunflower to break the development cycle of the pest.
- Delay sowing, where practicable, to allow the crop to escape from high populations.
- Apply neem; it has been shown to reduce flea beetle numbers and damage.