Beanflies (Ophiomyia centrosematis and O. phaseoli)
Bean flies are (about 2mm long) flies, shiny black-bluish in colour. Female flies lay eggs on young leaves, piercing the leaves and sucking the exuding sap resulting in yellow blotches on the leaves, which are the first signs of bean fly attack and are useful for early detection of this pest. Maggots mine their way from the leaves down to the base of the stem, where they complete their development. Maggot feeding destroys the tissue causing the steam to swell and split and reducing formation of lateral roots.
Young seedlings and plants under stress wilt and die when attacked by bean flies. Older or vigorous plants may tolerate bean fly attack, but their leaves turn yellow, their growth is stunted and their yield reduced. Damage is more severe in plants growing under poor conditions such as infertile soils and drought. Under good conditions, soybean, however, can compensate for minor stand reductions; thus, small gaps dispersed in a field normally are filled by adjacent plants and no yield reductions are detected.
- Plant early in the season. Bean fly numbers tend to be low during the early stages of the growing season and increase with time.
- Provide favourable growing conditions to improve plant vigour and to enhance tolerance to bean fly attack.
- Avoid planting soybeans near cowpea, beans and other leguminous crops, that may be the source of bean flies.
- Remove and destroy crop residues and all plant parts with symptoms of damage by bean flies.
- Monitor the field shortly after emergence.
- Ridge the crop 2-3 weeks after germination. This helps to cover the adventitious roots, which are produced by plants damaged by bean flies. The soil support prevents lodging and improves the survival of the damaged plants.
- If necessary, spray neem extracts. Frequent foliar applications of neem extract give satisfactory control of bean flies.