Determination of Yield-Loss Relationships for Two Soybean Defoliators by Using Simulated Insect-Defoliation Techniques1

A 3-year study, from 1976 to 1978, was conducted in central Iowa to establish more accurate yield-loss relationships for the painted lady, Cynthia cardui (L.), and the green cloverworm, Plathypena scabra (F.), on soybeans. Simulated larval development and insect defoliation were driven by a temperature-dependent leaf-consumption model. Central Iowa experienced a severe drought during 1976 and 1977, and yield reductions those years were great. There was an ample supply of soil moisture during the remaining year, 1978, and the insect levels simulated did not cause any yield reductions. Therefore, yieldloss relationships were established only for the dry years when a moderate drought existed, as were the subsequently calculated economic-injury levels.