The Effect of Planting / Harvesting Periods and Seasons on the Dynamics and Damage by Sweet Potato Weevils in the S.W Region of Cameroon

Abstract

The sweetpotato Ipomoea batatas L. (Convolvulaceae) has been one of the most important foods in Africa and the rest of the world for centuries. The sweet potato weevil, Cylas puncticollis (Fabricius), is the most serious pest of sweet potato around the world, damaging sweet potatoes in the field and in storage. Because the larval period is spent within vines or tubers, and the adults are nocturnal, chemical control frequently is not effective. This study aims to determine the effect of different planting and harvesting dates on infestation of different sweet potato cultivars by the weevils so as to better time planting and or harvesting for maximum yield and least infestation. Currently, little or no information is provided to growers in Cameroon on the best periods of planting and harvest.  Ten sweet potato cultivars were planted in different planting periods i.e April – June, July – September for the wet season and October – December, January – March for the dry season. The vines and storage roots were observed for infestation by SPW during the two seasons in 2012. Planting was repeated in 2013 in the two seasons (wet and dry) to determine the harvesting period with the least infestation on the storage roots. Results showed a significance difference on the percentage infestation and yield (P< 0.05) amongst the various planting periods with the least infestation registered during the July – September planting periods (0.3%) while the highest infestation was realized in the planting period of January – March (9.22%). The best yield was observed in the period of April – July (12.85 tons/Ha) while the least yield was recorded in the planting period of July – September. The difference in vines damage throughout the planting periods was not significant at (P > 0.05). Delayed harvesting during the rainy season registered minimum infestation (0%) but increased (9.1%) as we approached 135 DAP while infestation was all through high during the dry season during harvest and continued to increase as harvesting was delayed above 90. Sex ratio of weevils throughout the wet and dry seasons showed a higher ratio of females all through but decline to zero during the peak of the rainy season.

Keywords: Sweetpotato Ipomoea batatas L., Cylas punticolis, Planting periods, Dry season, Wet season, Percentage infestation.