Biology and Control of the Sorghum Midge. 3. Importance of Stage of Bloom and Effective Residual of Selected Insecticides12

Abstract

Grain sorghum, Sorghum bicolor (L.) Moench, boots were covered with pollination bags prior to head emergence and a series of 10 bags were removed at 4 stages of grain head development to subject them to attack by field populations of the sorghum midge, Contarinia sorghicola (Coquillett), for a 24-hr exposure period. Seed damage patterns indicated that minor oviposition occurred prior to the appearance of blooms and after most blooms had been sheet. Maximum egg deposition occurred during the 24-hr exposure period when the heads were in 50% yellow and 50% red blooms. Tests of the control effectiveness of residues of 4 insecticides were made in plots with heads protected from midge, treated, and then recovered with pollination bags or net cages. Heads were subsequently exposed to field midge populations or to midges introduced into the cag’s at 24-hr intervals. Results indicated that all insecticides were effective for 48 hr. Parathion was much less effective by the 3rd day, carbophenothion by the 4th day, and disulfoton and endrin by the 5th day, demonstrating the need for a minimum 3-4 day interval in the spray schedule for midge control when using some of these compounds.