INTEGRATION OF PLANT-RESISTANCE, INSECTICIDES, AND PLANTING DATE FOR MANAGEMENT OF THE HESSIAN FLY (DIPTERA, CECIDOMYIIDAE) IN WINTER-WHEAT

The Hessian fly, Mayetiola destructor (Say), can cause severe damage t o soft red winter wheat, Triticum aestivum L. em Thell, in the southea stern United States. The efficacy and cost effectiveness of in-furrow applications of disulfoton and phorate as alternatives to planting dat e modification and plant resistance for controlling Hessian fly damage in winter wheat was studied during the 1987-1988 and 1988-1989 season s near Midville and Plains, Ga. The study consisted of a split-split p lot design of two planting dates, three insecticide treatments, and fo ur or six cultivars of soft red winter wheat. Populations were small a nd damage was minimal during the first season, but populations were la rge and damage was severe during the second season. Planting before th e recommended planting date increased the severity of Hessian fly inju ry, but planting at the recommended date did not necessarily avoid Hes sian fly damage during the fall. Applications of phorate and disulfoto n were equally effective in controlling infestations in the fall and w inter. Spring infestations also tended to be lower in treated than unt reated plots. Plant resistance controlled Hessian fly damage throughou t the season. Phorate reduced wheat seedling establishment in some tri als, but this reduction did not adversely affect wheat productivity an d economic returns. Low populations had little effect on wheat yield, test weight, and economic returns in 1987-1988. Hessian fly damage in 1988-1989 reduced grain yield, test weight, and straw weight in untrea ted susceptible cultivars. Use of a systemic insecticide at planting o n Hessian fly susceptible cultivars provided a positive economic retur n regardless of planting date, and disulfoton and phorate provided sim ilar economic benefits. When infestations were large, resistant cultiv ars provided a large economic benefit compared with an untreated susce ptible cultivar. Insecticide use on a resistant cultivar was not econo mically justified. Planting a high-yielding, resistant cultivar withou t an insecticide provided similar or better economic returns than othe r management options. However, if high-yielding resistant cultivars ar e not available, use of a systemic insecticide at planting on suscepti ble cultivars in conjunction with proper cultural practices is a cost- effective alternative approach to managing the Hessian fly in wheat.