Control of chironomid larvae (Diptera: Chironomidae) in establishing rice crops using starch-based chlorpyrifos pellets.

Starch-based pellets containing 10% (w/w) chlorpyrifos were evaluated for control of chironomid larvae in rice crops immediately after flooding. Chlorpyrifos pellets at rates of 2.0, 3.5, and 6.0 kg/ha (0.2, 0.35, and 0.6 kg AI/ha), and, as a reference treatment, 150 ml/ha of 500 g/liter chlorpyrifos emulsifiable concentrate (EC) (0.075 kg AI/ha) were evaluated in New South Wales, Australia. The pellets reduced total midge larvae by 93-94% over the initial 36 days posttreatment, with some indication of residual control 50 days posttreatment at all rates. Chironominae were reduced by 80-85%, and other chironomids (predominantly Tanypodinae) by 98% during the first 36 days posttreatment. Increasing the pellet application rate above 2.0 kg/ha did not improve control. Although the EC formulation provided 100% control of all larvae for 12 days, control declined thereafter. The EC formulation reduced total larval numbers by 55% over the first 36 days posttreatment, with Chironominae increasing by 28% and other chironomids being reduced by 84%. Significantly (P < 0.05) higher water column toxicity levels were recorded for the EC formulation in the first 3 days after application.