Browsing by Author "John Eias Sariah"

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Studies on influence of sowing time of beans (phaseolus vulgaris) on level of infestation and parasitism of the bean stem maggot
(Sokoine University of Agriculture, 2003) John Eias Sariah
The influence of time of sowing of beans, Phaseolus vulgaris, on level of infestation and parasitism of the bean stem maggot (BSM) (Ophiomyia spp) was studied during off-season cropping of beans at Madira farm, Tengeru. Two bean varieties, Lyamungu 90 and ZPV 292, which are susceptible and tolerant to BSM, respectively, were sown in the field. 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 due to infestation were established. Ophiomyia spencerella were the dominant bean fly maggots infesting the crop. Sowing dates had significant (p 0.001) influence on BSM infestation. Early sown beans experienced low BSM infestation. The bean variety ZPV 292, was relatively less infested. Braconids were the dominant parasitoids and the relationship to the host population was density dependent. Parasitism reduced emergence of BSM by about 68%. Variety and sowing time (factor) interaction had no significant (p > 0.05) influence on BSM infestation and natural enemies parasitism. The study shows that timely sowing of beans enable the crop to escape peak population of BSM at the most vulnerable plant growth stage. The study further shows that natural parasitism by Braconids play an important role in maintaining a low population of BSM.