Wednesday, November 15, 2006

Early Season Insect Defoliation Influences the Critical Time for Weed Removal in Soybean.

Steven Knezevic, Haskell Agricultural Laboratory, 57905 866 Rd., Concord, NE 68728-2828 and Travis Gustafson, Univ. of NE, Lincoln, NE 68583.

 In order to develop more effective pest management strategies, it is essential to understand how different pests interact with each other and the crop.  Field studies were conducted in 2003 and 2004 at two Nebraska locations to determine the effects of early season crop defoliation on the critical time for weed removal (CTWR) in narrow row soybean.  Three soybean defoliation levels were selected to simulate 0%, 30%, and 60% leaf tissue removal by the bean leaf beetle.  Weeds were allowed to compete with the crop until V2, V4, V6, R3, and R5 growth stages.  There were also season long weedy and weed-free treatments.  Results indicated that the CTWR in soybean occurred earlier as defoliation levels increased from 0 to 60%.  The CTWR occurred at V3, V2, and V1 growth stage for 0%, 30%, and 60% defoliation levels, respectively.  Overall, 60% defoliation resulted in earlier CTWR by at least 14 d.  Yield losses from defoliation and weed interference were primarily associated with a reduction in number of pods plant-1.