Abstract:
The sweetpotato (Ipomoea batatas L.) is one of the most important food crops in Africa
and the world that is in Tanzania produced in largest quantities in the central Regions
where, however, yields are very low due to abiotic and biotic constraints. One of the most
serious biotic constraints is the sweet potato weevil, an insect whose cryptic feeding
nature of the very destructive larval stages makes chemical control often not effective. A
survey was conducted in two Districts of central Tanzania (Ikungi – Singida and Gairo -
Morogoro) to map the sweet potato weevil distribution and damage incidences. Ten
villages in each District were randomly selected whereby three farmers in each village
were interviewed and their fields intensively assessed for weevil infestation. Results
showed varying distribution of weevils with locations (villages) surveyed. Gairo District
was having more weevil infestation and damage incidences than Ikungi District. Due to
the nature of damage in both vines and roots it was concluded that the species available in
the area is Cylas spp. Further study was conducted to establish variety response to the
weevil infestation at different times of planting. Four sweetpotato varieties were tested for
weevil infestation in three timings of planting (December, January and March). Again,
adult weevils were captured in traps throughout the growing season. Significant
differences in percentage weevil infestation and yield amongst various planting periods
was observed (P≤0.05) with the least infestation registered in December while the highest
infestation was realized in March planting. Simama variety was most susceptible to weevil
infestation followed by Polista and Mataya while Gudugudu was least susceptible. Despite its susceptibility, however, Simama yielded the highest. The weevil capture experiment suggested existence of only one species in central Tanzania, whose distribution was uneven among the two Districts. This species was Cylas puncticollis. Trends of population build up in the study locations indicated that adult weevils increased progressively along the growing season. The study concluded that Cylas puncticollis will remain a problem in sweetpotatoes in central Tanzania. Concerted efforts in form of IPM and education to farmers are required to minimize the pest’s damaging effects.
