Timely application of postemergence products is critical to protect corn yields, especially in fields relying solely on postemergence herbicides. Weeds can begin to affect yields as early as two weeks after crop emergence. The specific time at which weeds begin to reduce yields varies widely depending upon many factors, but the longer application is delayed, the greater the risk of a yield penalty.
Iowa State University
Hartzler, Robert G., "Importance of timely scouting for weeds" (2005). Integrated Crop Management News. 1368.
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