Does the systemic insecticide imidacloprid (Gaucho) have a direct effect on yield of grain sorghum?

Gaucho' (imidacloprid; 1-[(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazoli dinimine) is a seed treatment insecticide widely used on sorghum [Sorghum b icolor (L.) Moench] to control a number of pests, including greenbugs [Schi zaphis graminum (Rondani)], chinch bugs [Blissus leucopterus leucopterus (S ay)], and wireworms (Limonius sp.). A series of tests was conducted at five locations in Kansas during 1996 and 1997 and three locations during 1998 t o determine whether a yield response results even in the absence of pests w hen Gaucho is used as a seed treatment on grain sorghum. Results varied. Ga ucho improved yields at Hesston, especially in the June plantings but some hybrids benefited more than others. These differences may have been due to chinch bugs that were observed in the plots and were known to be troublesom e in the area. Because their numbers were low, other factors may have playe d a role. At the other locations and in the absence of chinch bugs, Gaucho had less of an influence on yields. At Garden City, where some greenbugs de veloped, Gaucho provided early-season control, but infestations were too li ght to influence yields. At Hays, Gaucho treatments appeared to have some i nfluence on the numbers of corn earworms [Helicoverpa tea (Boddie)] in sorg hum heads in one planting, although yield differences were not significant. Overall, this study found no consistent yield increases in fields treated with Gaucho in the absence of observable pest activity.