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Title: ECONOMIC INJURY LEVEL FOR THE GREENBUG, SCHIZAPHIS GRAMINUM, IN OKLAHOMA WINTER WHEAT

Author
item Kindler, Dean - Dean
item Elliott, Norman - Norm
item GILES, K - OKLAHOMA STATE UNIV
item ROYER, T - OKLAHOMA STATE UNIV

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2003
Publication Date: 9/1/2003
Citation: Kindler, D., Elliott, N.C., Giles, K.L., Royer, T.R. 2003. Economic injury level for the greenbug, schizaphis graminum, in Oklahoma winter wheat. Southwestern Entomologist. 28(3):163-166.

Interpretive Summary: The greenbug is a serious insect pest of wheat that causes extensive monetary losses to wheat growers. The economic injury level is defined as the density of the pest that causes monetary losses greater than the cost of treating the field with insecticide. Knowledge of the economic threshold is essential if insecticides are to be used only when needed, as part of an economically and environmentally sound pest management program. In this study, we determined the economic injury level of greenbugs in winter wheat in Oklahoma during a four-year study of the effect of greenbug feeding on the yield of winter wheat. Each year, study plots were established and infested with varying numbers of greenbugs during the fall and during spring. Data obtained from the study were used to develop a mathematical model of yield loss in relation to the number of greenbugs occurring per wheat stem. The model predicts a 14.5 kg/ha (0.22 bu/ac) loss of yield for each greenbug per stem during years with near normal precipitation, and loss of 34.3 kg/ha (0.51 bu/ac) under severe drought conditions. This model paves the way for more economical management of greenbugs in winter wheat by providing managers with the information they need so that insecticides can be applied only when there are monetary benefits for doing so.

Technical Abstract: The effect of greenbug, Schizaphis graminum (Rondani), feeding on the yield of winter wheat cultivars was studied during four years in central Oklahoma. Each year, a 0.4-ha planting of 'Karl' (1993), 'Karl-92' (1995, 1996, and 1997), or '2163 (1997) winter wheat was made between October 1 and 15. One-meter square plots were established and infested with varying numbers of biotype-E greenbugs during the three- to four-leaf growth stage (fall infestations) or during the tillering growth stage in late winter (spring infestations). Greenbug infestations achieved in plots by artificial infestation were great enough to affect the wheat yield from infested plots, but the intensity of infestations varied among years and growing seasons. A regression model was constructed to estimate yield loss for the cultivars tested as a function of the maximum number of greenbugs occurring per tiller in the plot. The regression model predicted a 14.5 kg/ha (0.22 bu/ac) loss of yield for each greenbug per tiller during years with near normal precipitation, and a loss of 34.3 kg/ha (0.51 bu/ac) under severe drought conditions.