Managing Corn Rootworms: (Coleoptera Chrysomelidae) on Dairy Farms: the Need for a Soil Insecticide

Abstract

Field trials were conducted at 20 locations in New York during 1993 and 1994 to evaluate the effects of using manuring practices and soil insecticide on rootworm injury, plant height, lodging, and yield of corn. All fields had adult densities of western corn rootworm, Diabrotica virgifera virgifera LeConte, exceeding 1 beetle per plant during the year preceding the test. The following 4 treatments were tested: (1) inorganic fertilizer, (2) inorganic fertilizer plus soil insecticide, (3) manure, and (4) manure plus soil insecticide. Root injury was significantly reduced by soil insecticides during both years but was unaffected by manure treatments. Both manure applications and soil insecticides increased plant heights during June and July. The effect of treatments on yields differed by year. In 1993, soil insecticides significantly increased silage yields an average of 3.05 metric tons (MT)/ha but had no effect on grain yield. In contrast, manuring did not significantly affect either silage or grain yield. In 1994, silage yields were 3.45 MT/ha higher in manured treatments compared with nonmanured treatments. Soil insecticides increased silage yield 2.3 MT/ha in nonmanured treatments but did not affect silage yield in manured treatments. Grain yields were not affected by either insecticide or manure treatments in 1993 but were significantly higher (4.7 quintals/ha) in insecticide treatments in 1994. The effect of manure on corn tolerance to western corn rootworm seemingly is greater during years when corn is not under moisture stress. Multiple regression models, incorporating soil characteristics, nutrients in fertilizers, and planting information, were developed to predict crop yield and change in yield expected with the addition of a soil insecticide. Yield models also suggest the need for more controlled experiments to characterize directly the effects of drainage, potassium and phosphorus availability, pendimethalin herbicide injury, soil pH, and rainfall on soil insecticide benefits.