|Royer, T - OKLAHOMA STATE UNIV|
|Giles, K - OKLAHOMA STATE UNIV|
|Nyamanzi, T - OKLAHOMA STATE UNIV|
|Hunger, R - OKLAHOMA STATE UNIV|
|Krenzer, E - OKLAHOMA STATE UNIV|
|Payton, M - OKLAHOMA STATE UNIV|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2004
Publication Date: January 15, 2005
Citation: Royer, T.A., Giles, K.L., Nyamanzi, T., Hunger, R., Krenzer, E.G., Elliott, N.C., Kindler, D., Payton, M. 2005. Economic evaluation of the effects of planting date and application rate of imidacloprid for management of cereal aphids and barley yellow dwarf diseases in winter wheat. Journal of Economic Entomology 98(1):95-102. Interpretive Summary: Insecticides are used extensively for controlling aphid pests of wheat, such as the greenbug and bird cherry-oat aphid, and barley yellow dwarf disease (BYDV), which the aphids transmit. We conducted experiments with the insecticide seed treatment imidacloprid from 1997-1999 at two locations. In the first experiment, planting date and the rate of imidacloprid used to treat seeds were varied. In the second experiment two varieties of hard red winter wheat seed and four rates of imidacloprid treated seed were used. Aphid densities, occurrence of BYDV, and wheat yield were measured in the experiments. Yield differences were used to estimate the economic return obtained from using imidacloprid. The overall result of the studies was that imidacloprid seed treatment reduced aphid numbers and the incidence of BYDV, and sometimes resulted in a positive yield response. But the economic return from seed treatment with imidacloprid was variable, sometimes being positive and sometimes negative. Positive economic returns were more likely when wheat was planted early in the season rather than when it was planted later. Early planting is more typical for producers attempting to grow wheat for forage + grain as a "dual purpose" crop because wheat must be planted early in order to maximize forage production. Thus, growers plating dual purpose wheat are more likely to obtain economic benefits by using imidacloprid-treated seed. Growers planting wheat for grain only production, who typically plant at later dates to maximize yield, are less likely to receive economic benefits from imidocloprid seed treatment.
Technical Abstract: The effects of planting date and application dosage of imidacloprid on control of Schizaphis graminum Rondani, Rhopalosiphum padi L. (Homoptera: Aphididae) and barley yellow dwarf virus (BYDV) in hard red winter wheat were studied. The first experiment was conducted from 1997-1999 at two locations and consisted of three planting dates and four rates of imidacloprid-treated seed. The second experiment consisted of two varieties of hard red winter wheat seed and four rates of imidacloprid in Stillwater OK from 2000-2001. Aphid densities, occurrence of BYDV, yield components and final grain yield were measured, and yield differences were used to estimate the economic return obtained from using imidacloprid. In the first study, aphid populations responded to insecticide rate in the early and middle plantings, but the response was reduced in the late planting. Yield increased with insecticide rate but did not always result in a positive economic return. The results from the second study revealed that imidacloprid seed treatments reduced aphid numbers and BYD occurrence, increased yield, and resulted in a positive economic return. The presence of aphids and BYDV lowered yield by reducing fertile head density, total kernel weight, and test weight. These results suggest that imidacloprid reduces aphid numbers and incidence of BYDV, and may result in a positive yield response, but does not always consistently provide a positive economic return. Results indicated that producers attempting to grow wheat for forage + grain as a "dual purpose" crop are more likely to obtain positive economic benefits by using imidacloprid-treated seed.