Sorghum Midge (Diptera: Cecidomyiidae) Management with Resistant Sorghum and Insecticide

Abstract

Field evaluations were conducted in 1982 and 1984 to compare the efficacy of diazinon for control of sorghum midge, Contarinia Sorghicola (Coquillett), infesting resistant and susceptible sorghum hybrids. In 1982, diazinon application resulted in significantly higher yields of the resistant hybrid than the susceptible hybrid when the same treatments were made and midge density was high (ca. 50 per panicle). Highest yields of the resistant hybrid occurred when plants were treated five times at 3-day intervals, but greatest economic returns were obtained when plants were treated three times at 5-day intervals. Even when untreated, the resistant hybrid produced higher net returns than the susceptible hybrid following any of the diazinon treatments. Although percent yield improvement of treated sorghum was higher for the susceptible hybrid than the resistant, the susceptible hybrid yielded only as much as the untreated resistant hybrid, and only ca. 50% as much as the treated resistant hybrid. When midge densities were low, but above the economic injury level, yields of the resistent hybrid were about equal whether treated or untreated with insecticide. The susceptible hybrid yielded 50% as much as the untreated resistant hybrid and 25–50% less when both hybrids were treated the same. When variable diazinon applications were based on percent panicle flower, and when midge density was high, the resistant hybrid responded more efficiently to the diazinon treatments in terms of yield and net value compared with the susceptible hybrid.