Effect of sowing time on infestation of beans (Phaseolus vulgaris L.) by two species of the Bean Stem Maggot, Ophiomyia spencerella and Ophiomyia phaseoli (Diptera: Agromyzidae)

Abstract

The influence of time of sowing on the level of infestation of beans, Phaseolus vulgaris (L), by two species of the bean stem maggot (BSM), Ophiomyia spencerella (Greathead) and O. phaseoli (Tyron) (Diptera: Agromyzidae) was investigated during off-season cropping of beans at Madira Farm, Arusha Region, in northern Tanzania. Two bean varieties, Lyamungu 90 and ZPV 292, which are commonly cultivated in the area, were sown and their susceptibility to BSM was assessed. Three sowing dates were adopted; early, normal calendar and late sowing in a split-plot design. The abundance of BSM pupae in bean stems and the number of cracked stems (stem lodging) due to infestation were established. O. spencerella were the dominant bean stem maggots infesting the crop, whereas O. phaseoli infestation was relatively low. Sowing dates had significant (p < 0.001) influence on BSM infestation. The early-sown beans experienced low BSM infestation while the late-sown beans had significantly higher infestation levels. The bean variety ZPV 292 was relatively less infested compared to Lyamungu 90 and was considered tolerant to BSM infestation. Since sowing time had significant effects on BSM infestation, sowing of beans early in the season would enable the crop to escape the peak population of BSM during the most vulnerable growth stage and therefore reduce the effects of the pest on the crop significantly.