Effects of insecticides and cultivars on panicle-feeding insect pest infestations and grain yield of sorghum (Sorghum bicolor (L.) Moench) in northern Ghana

Abstract

Panicle-feeding insects are a challenge in sorghum (Sorghum bicolor (L.) Moench) cultivation but most farmers do not protect the crop. Here, the effects of pest management in different sorghum cultivars on grain yields and the financial returns after protecting the crop from panicle-feeding insects was studied. There were significant insecticide treatments × cultivars/genotypes interaction effects for Stenodiplosis sorghicola, Clavigralla tomentosicollis, Nezara viridula, Dysdercus fasciantus and Riptortus dentipes. Generally, pest infestations were higher in the untreated control compared to K-Optimal- or NSO-treated sorghum. Infestations were also higher in compact-headed cultivars (Dorado and Kapaala) compared to those with open heads (CSSOR 08-V01 and CSSOR 10-V07). Damage was approximately 1.7-fold higher in the untreated controls than in NSO or K-Optimal. Grain yields were about 14% higher in NSO or K-Optimal treated sorghum than in controls. Gross margins were between 16- and 35-fold higher in protected sorghum compared to the untreated ones. These findings suggest that an effective integrated pest management strategy for sorghum farmers must comprise cultivars that do not have compact heads, and the use of about two sprays of NSO or a synthetic pyrethroid when high numbers of panicle-feeding insects are observed during the growing season. Judicious use of insecticides and the “right” cultivar will improve the profitability of sorghum farmers with gross marginal returns that are at least 15-fold higher than that obtained by farmers who adopt only good agronomic practices without insecticide sprays.