Figure 1. Weed escapes in soybean treated with a single preemergence herbicide application of Outlook and Pursuit on May 5. Photo taken August 6.
With waterhemp becoming more widespread throughout the state and glyphosate resistance increasing, how do your soybeans look this fall? If they look like Figure 1, it may be time to change your weed control strategy.
One strategy for dealing with glyphosate resistant waterhemp is to layer soil residual herbicides. This approach is being evaluated in Rochester, Minnesota and includes a number of residual herbicides in single and two-pass applications. The herbicides in the trial include 1) Dual (s-metolachlor), 2) Outlook (dimethenamid-P), and 3) Warrant (acetochlor). They were selected because of their known effectiveness for controlling waterhemp and their flexibility in application timing. Pursuit (imazethapyr) does not control this population of waterhemp (ALS resistant); however, it was applied in tank mixes with the pre-emergence herbicides to eliminate other broadleaf weeds.