Spring conditions across Minnesota are finally allowing soybean planting to begin in many areas. As planters start to roll, now is the time to make sure your pre-emergence (PRE) herbicide program is in place. PRE herbicides remain one of the most important, and often underutilized, tools for managing weeds and protecting soybean yield potential.
In recent years, many soybean acres across the Upper Midwest have relied heavily on POST-only herbicide programs. However, this approach is increasingly risky. The spread of herbicide-resistant weeds, including resistance to glyphosate and other commonly used POST chemistries such as ALS- and PPO-inhibitors, has made a one-pass POST strategy unreliable in many fields. With the recent confirmation of glufosinate-resistant waterhemp in Minnesota, we are now facing the very real possibility of waterhemp populations with little to no effective POST herbicide options remaining. For more information on this discovery, see the recent Minnesota Crop News article covering the first confirmed case of glufosinate-resistant waterhemp in the state.
Why PRE herbicides matter
Research across the Midwest shows that soybeans must be kept weed-free from emergence through the V3 to V4 growth stage to avoid yield loss. This period represents the critical window of weed control (Van Acker et al., 1993; Badger Crop Network, 2025). While weeds emerging after V4 may have less impact on yield, they can still produce seed and contribute to future infestations, reinforcing the importance of a “start clean, stay clean” approach.
This is especially important for waterhemp, one of the most challenging weeds in Minnesota soybean systems. Waterhemp has a prolonged emergence pattern, with new flushes continuing well into the growing season. As a result, relying solely on POST herbicides often means chasing multiple cohorts of weeds, many of which may already be too large for optimal control or may carry herbicide resistance traits.
Source : umn.edu