Studies on influence of sowing time of beans (phaseolus vulgaris) on level of infestation and parasitism of the bean stem maggot
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Date
2003
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Publisher
Sokoine University of Agriculture
Abstract
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.
Description
Dissertation
Keywords
Sowing of beans, Phaseolus vulgaris, Off-season cropping, Parasitism, (BSM) (Ophiomyia spp), Madira farm, Tengeru