Effect of intercropping, earthing-up and harvesting periods on the management of sweet potato weevil, Cylas puncticollis B. (Coleoptera: Curculionidae) at haramaya, Ethiopia

Abstract

Sweet potato weevil, Cylas puncticollis (Boheman) is the most serious destructive pest that ranks as the number one constraints for the production of Sweet potato in Eastern Ethiopia. It attacks the Sweet potato stems and storage tubers, both in the field and storage. Control of this serious pest by chemical is too difficult due to the cryptic nature of larvae and nocturnal activity of the adult insect. In this study, field experiment was conducted with the aim to develop environmentally friendly and economically feasible IPM methods of Sweet potato weevil in eastern Ethiopia. Three levels of cropping systems (sole Sweet potato (as control), Sweet potato with maize and Sweet potato with haricot bean), three levels of earthing-up (1time, 2times and 3times) and two levels of harvesting periods (prompt and 1 month delayed harvesting) and were laid-out in randomized complete block design (RCBD) with three replications in a factorial arrangement. The experiment was conducted at Haramaya University in East Hararge (East Ethiopia) under natural infestation during the rainy season (July-Nov.) of 2011 with two rows of maize/haricot-bean planted within Sweet potato rows. Data were collected on infestation of C. puncticollis, number of weevils, number of storage tubers with weevil damage, weight of healthy and damaged tubers, number of marketable and unmarketable tubers. Data were analyzed using SAS version 9.2 and means were separated using least significant differences (LSD). Results of the studies revealed that the interaction effect of intercropping, earthing-up and harvesting period were highly significantly (p<0.01). Intercropping with maize, three times earthing-up and prompt harvesting has reduced percentage infestation from (92.33 to 14.33%), % weight loss from (68.28 to 8.46%), % yield loss from 70 to 22.26% and increased number of marketable tubers per plant from 1.8 to 9.67. Intercropping with maize, two times earthing-up and prompt harvesting reduced % of damaged storage tubers (59.45 to 5.52%). Strong cause-effect (R2 =0.94) exist between percent damaged tubers and number of weevils per kilogram of damaged storage tubers. Intercropping Sweet potato with maize resulted in minimized infestation than with haricot bean in combination with three times earthing up and prompt harvesting. The highest (1.53) land equivalent ratio (LER) was obtained from Sweet potato-haricot bean intercropping followed by Sweet potato-maize (1.28) cropping system. Similarly, cost-benefit analysis showed Sweet potato intercropped with haricot bean resulted in high economic profit than Sweet potato with maize and monoculture. However, the yield of Sweet potato was affected by maize intercropping and higher in their sole crops. Therefore, there is a need for further improvement study to develop and implement an IPM of Sweet potato weevil for immediate solution and speedy adoption in Eastern Ethiopia (East Hararge).