Many sunflower fields across the state are far enough along in their development that the window for preventing weeds with residual herbicides has passed. At this point in the season, emerged kochia, Palmer amaranth, waterhemp, or other broadleaf weeds are not just a current-year concern, they are also an indication of where future weed management plans may need to improve.
Weed escapes that remain in the field through the remainder of the growing season can contribute seed back to the soil seedbank. This is especially concerning for species such as Palmer amaranth, waterhemp, and kochia, which can produce large amounts of seed and have developed resistance to commonly applied herbicides. Meanwhile, sunflower production adds complexity to this existing problem, because postemergence herbicide options are already limited. When resistant weeds emerge with or shortly after the crop, rescue options may not provide the level of control producers are hoping for.
Residual herbicides can be a useful tool in combatting these weeds, but they are most effective when they are used before weed emergence. In high-risk fields, these applications need to be planned around crop stage, weed emergence, herbicide label restrictions, and rainfall needed for activation, to extend control of weeds later into the season. For this reason, residual herbicides should be viewed as part of a proactive weed management plan rather than a rescue treatment after weeds have already emerged.
In fields where herbicide-resistant weeds are becoming more common, long-term management should not rely on a single herbicide pass, or active ingredient. Instead, producers should consider a more holistic approach, including crop rotation, multiple effective sites of action, timely residual herbicides, field scouting, and seedbank management as parts of the same strategy.
While it may be too late to prevent many of this year’s weed escapes, it is not too late to learn from them. Taking note of where weeds survived, which species are present, and which herbicide programs were used can help producers make better management decision before next year’s crop is planted.
