| Soybean leaf damage affects not only the final yield, but also the timing of when weed control needs to be initiated to prevent further yield loss. |
The basic philosophy of IPM is to use a combination of cultural, mechanical, biological, genetic and chemical methods for effective and economical pest control. In most crop production fields there are many species of weeds and insects with different life cycles and survival mechanisms, and it is not likely that they can be managed by a single control measure.
In reality, weeds and insects interact and affect not only each other and the crop, but also the efficacy of their respective management tactics. For example, insect-induced defoliation can significantly delay soybean canopy development, which in turn provides more sunlight for weeds to grow and compete with the crop, directly affecting subsequent weed management plans. Learning how insects and weeds interact with each other and the crop is essential in developing IPM strategies.
How insect defoliation affects weed control timing
UNL conducted research in 2003 and 2004 to determine the critical time for weed removal as influenced by the three levels of simulated insect defoliation (0%, 30%, and 60%). Results indicated that the insect damage to the soybean leaf area indeed resulted in a need for earlier weed management. For example, with no insect damage to the soybean canopy, weeds could remain in the crop up to the V4 stage (third trifoliate) or about 20 days after crop emergence without significantly affecting the yields. However, at the 30% and 60% defoliation levels, the research showed that weeds should be removed by the V3 (17 days) and V1 (10 days), respectively.
Early season insect control
From a practical standpoint, this indicates that soybeans with 30-60% of insect damage do actually have a shorter weed control window and potentially fewer weed control options. Soybean leaf damage affects not only the final yield but also the timing of when weed control needs to be initiated to prevent further yield losses. This research also shows that the producer may now have another tool to fight weeds in his soybean field – a good insecticide. If there is a particularly bad infestation of bean leaf beetle, spraying an insecticide to control the bean leaf beetle may actually widen the herbicide application window and increase weed control options for the producer.
Funding for this research was provided by the Nebraska Soybean Board.
Stevan Knezevic
Extension Weeds Specialist
Haskell Ag Lab, NEREC
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| Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture. | ||
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