Effect of Thimet against wheat stem sawfly, Cephus cinctus

Wheat stem sawfly Cephus cinctus (Hymenoptera: Cephidae) is a major pest of wheat grown in Montana. The larva feed within the stem until the plant is nearly mature then cuts the base of the stem allowing the wheat to fall over, the duration of this period varies with host plant phenology. The life cycle of the wheat stem sawfly and length of the hatch explains the difficulty in controlling its population because all immature stages are protected within wheat stems and adult females do not feed, leaving contact insecticides for control. Unpublished studies in Montana reported that systemic seed treatments of imidacloprid applied at varying rates and foliar-applied chlorpyrifos, carbofuran, and cyhalothrin-lambda had no significant effects on sawfly survivorship. Field experiments were carried out to study the effects of Thimet 20-G against C. cinctus on the winter wheat variety Yellowstone and spring wheat varieties, Duclair (solid stem) and, Vida, (hollow stem). Winter wheat application rates were applied as layby (between rows) treatments of 2.79, 3.96, and 5.58 Kg/ha at Feeke’s growth stage 5. Five treatment rates were used for spring wheat. There were treatments applied at planting and as layby treatments when the spring wheat was at Feeke’s growth stage 2.3. The experiments are in progress and results will be discussed.