Modeling the impact of sweetpotato weevils on storage root yield
This study estimated the amount of loss in storage roots caused by various levels of damage caused by sweetpotato weevils (Cylas spp). Seven varieties of sweetpotato (Ipomoea batatas L. (Lam)) were evaluated in three production sites in northern Ghana for two years (2014 and 2015). Yield data for each experimental plot were collected. A regression analysis was carried out using the generalized linear model approach. In the study, nonmarketable roots were classified as all undersized roots (<100g) and spoilt roots due to weevil, millipede, and soft rot. The results indicated weevil damage as the only significant predictor of nonmarketable yield at 5% level of significance. From the study, the average values for total root yield, marketable root yield, and nonmarketable root yield were 9.39, 6.71, and 2.67 ton/ha respectively. The minimum weevil damage (score 2) resulted in a yield loss of 2 ton/ha which represents 8.3% while severe damage at score 9 could cause a loss of 7.43 ton/ha of storage roots representing 31% of the attainable yield of sweetpotato. Weevil susceptibility needs to be treated as a serious trait when evaluating sweetpotato genotypes to be released as varieties.