Impact of defoliation on the agronomic performance of sweetpotato in Uganda

Abstract

The sweetpotato butterfly, Acraea acerata Hew. (Lepidoptera: Nymphalidae) is known to extensively defoliate the sweetpotato crop, especially during the dry season, and this leads to significant foliage yield reductions. However, storage root yield losses due to the defoliation have not been adequately quantified. Artificial defoliation studies were undertaken at Namulonge in central Uganda, to estimate the effect of frequency and timing of defoliation on the agronomic performance of sweetpotato (Ipomoea batatus). Results showed that defoliation had no effect on shoot survival. Single quality defoliations had little effect on storage root yield but repeated defoliations significantly (P<0.05) reduced root yield. The time at which defoliation was carried out did not have a significant effect on the yield. It is possible that the plants had sufficient time to recover when defoliated once and therefore were able to channel enough assimilates towards the roots. However, repeated defoliation may not have given the plants enough time after each regeneration, given the limited growth period of six months. Any recommendation for the control of A. acerata should therefore take into account these responses given the fact that defoliation by the pest is usually less severe than was the case in this study.



Key Words: Acraea acerata, Ipomoea batatus, shoot survival, sweetpotato butterfly


(African Crop Science Journal 2001 9(1): 103-108)