Impact of imidacloprid treated seed and foliar insecticide on Hessian fly abundances in wheat ( Triticum aestivum L.)

Wheat, Triticum aestivum L., is a major crop of economic importance throughout the United States. The Hessian fly, Mayetiola destructor (Say), is a common economically important pest, feeding on wheat in the larval stage through the southeastern US. It is a multi-voltine species, with generation number dependent on temperature. Growers rely on various management approaches such as resistant wheat varieties, crop rotation, timely plantings, and insecticide treatments to control this destructive pest. The objectives for this research were to show the efficacy of a common insecticide seed treatment (imidacloprid) and a common foliar insecticide spray (lambda-cyhalothrin) on Hessian fly abundance in wheat. Four experiments were conducted over two years in North Carolina, in order to manipulate Hessian fly abundance. Small plot studies were designed with whole plot treatments including non-treated and imidacloprid treated wheat seed, and subplots split with a semi-monthly foliar lambda-cyhalothrin application or no foliar insecticide. The number of Hessian fly eggs present on leaves, number of larvae, number of pupae, and tiller density were counted for the fall generation(s) and all plots were sprayed with foliar insecticide during the spring. Wheat seed treated with imidacloprid had fewer eggs, larvae, and pupae compared to other non-treated seed. With one exception during 2014, foliar spray applications did not reduce egg, larvae, and pupae abundance. Warmer temperatures during 2015 experiments provided conditions that extended Hessian fly presence, allowing multiple fall generations to infest wheat. Unlike 2014 experiments, foliar sprays in 2015 experiments provided some protection from Hessian fly.