Effect of planting dates on the population dynamics of Cylas puncticollis and sweet potato storage roots damage in South Western Cameroon

Abstract

The sweetpotato Ipomoea batatas L. (Convolvulaceae) is one of the most important food crops in Africa and the world. The weevil, Cylas puncticollis (Fabricius), is the most destructive field and storage insect pest of sweet potato in Africa. Because of the cryptic feeding nature of the very destructive larval stages, chemical control is often not effective. A field study was therefore designed to determine the effects of different planting dates on infestation and damage of various sweet potato cultivars by the weevils in South Western Cameroon. Ten sweet potato cultivars were planted in different months i.e April and July for the wet season and October and January for the dry season in 2012 and 2013. The vines and storage roots were observed for C. puncticollis damage. Results showed a significance difference on the percentage infestation and yield (P< 0.05) amongst the various planting periods with the least infestation registered for the July (0.3%) while the highest infestation was realized in the January planting (9.22%). The highest yield was obtained from the April planting (7.22 tons/Ha) and the lowest was recorded for the October planting (4.92 tons/Ha). Differences in vine damage amongst the planting periods were not significant at (P > 0.05). Delayed harvesting during the rainy season led to only slight (9.1%) increase in C. puncticollis infestation at 135 DAP while the infestation was high during the dry season at harvest and further increased as harvesting was delayed more than 90 DAP. Sex ratio of weevils throughout the wet and dry seasons showed a higher ratio of females.

Key words: Sweetpotato Cylas puncticollis, Planting dates, Percentage infestation.