Weed Control in Row Crops, a July 1 Assessment (07/08/21)
The Monday rain event meant some much-needed office time for administration. The rain event also created an opportunity to compared weed management observations with Dr. Joe Ikley. Joe made the first provocative statement of the conversation by declaring soil residual herbicides may have over-performed despite the very limited number of rainfall events to incorporate herbicides into the soil. I agreed!
My team and I installed experiments at three locations near Fargo/Moorhead to evaluate waterhemp control in sugarbeet, utilizing a program approach for weed management including preemergence, early postemergence, and postemergence herbicides. Waterhemp control continues to range from 80% to 90%, 55 to 70 days after planting despite erratic sugarbeet emergence due to dry soils at planting and soil residual herbicides remaining on the soil surface two to three weeks after planting. The key in sugarbeet was at least partial incorporation of preemergence herbicide enabling control of the first flush of waterhemp as compared to no preemergence herbicide. The laybys and postemergence herbicides without preemergence herbicides at planting provided less than 85% waterhemp control.
Joe observed similar results from preemergence followed postemergence combinations in corn, soybean, and dry bean. Joe stated postemergence herbicides alone have provided erratic weed control due to a combination of factors including cooler than normal air temperatures in May, warmer than normal air temperatures, low humidity conditions, and drought conditions that has thickened the plant cuticle and/or have altered plant architecture. We both have observed less than acceptable common lambsquarters control, even with glyphosate products. Finally, we discussed reduced control of weed in sprayer wheel tracks and adjacent areas due to poor spray deposition, excessive dust, or a combination of both.
Why surprisingly good weed control from a program approach? We believe the preemergence herbicides, although not adequately incorporated by rainfall into the soil provide just enough control of early germinating small seeded broadleaf weeds. The lack of rainfall in May and June likely reduced germination and emergence of small seeded broadleaf weeds like common lambsquarters and waterhemp that emerge from the surface to up to 1-inch deep in soil. And soil residual herbicides remained on the soil surface, or the layered application of soil residual herbicide was incorporated by pop-up storms and controlled subsequent small seeded broadleaf weed flushes.
Sugarbeet rows are closing in many areas signaling the transition from weed management to control of leaf diseases in sugarbeet. However, corn, soybean and dry bean crops have not canopied, especially in drought-stricken areas meaning the final evaluation of #weedcontrol2021 will not occur for 4 to 6 weeks. Stay tuned for further weed control assessment and a data focused final assessment of weed control during late fall and winter meetings.
Extension Sugarbeet Agronomist
NDSU & U of MN