A dry spring helped keep weed populations down this year, but some of the usual suspects still made an unwelcome appearance. Early on, lambsquarters and giant ragweed popped up in Minnesota corn and soybean fields.
Perhaps lack of rain contributed to slower activation of preemergence herbicides and early hardening-off of weeds. As a result, if farmers weren’t timing applications properly and using the right tank mix partners, those weeds proliferated. Later, waterhemp emerged. In-season delays led to suboptimal postemergence herbicide application timing, forcing those herbicides to work, in many cases, on much larger weeds.
As we turn the page on this season, we should consider how this year’s weed pressures may inform next year’s management strategies. Here are some tips:
1. Manage resistance. Be sure you’re managing resistance with the proper herbicide, especially with waterhemp. If you applied a Group 14 herbicide or glyphosate postemergence on weeds this year and didn’t get control, are you going to spray it again or do a test for resistance? If you think you have resistance, talk with your local agronomist about what your plans should be for next season.
Additional consultation regarding resistance may be warranted, but table stakes for helping manage it is using herbicides with multiple modes of action (MOAs) at sequential timing.
2. If you used dicamba, have an alternative. This season provided ample opportunities for farmers to spray dicamba prior to our state’s June 20 cutoff. There were some windy days and potential for volatility in the field. However, farmers who used the right adjuvants and spray mixes and followed best management practices were able to spray successfully. As farmers are likely aware, there are still many unknowns, not just about dicamba but about different drift occurrences and how they happen.
Following best practices can help reduce those unknowns. However, if you’re looking to move away from a dicamba system next season, some alternatives include 2,4-D and glufosinate. Remember, we still also have glyphosate to help with grasses and Group 15 herbicides to help keep broadleaf weeds from emerging. Discuss options with your agronomist.
3. Pay attention to rotated fields. Most 2020 soybean acres with weed escapes are probably transitioning to corn, so make sure you have a high-quality foundational residual herbicide on your corn acres. Given that corn yield is responsive to its environment and what’s growing next to it, namely other corn plants or weeds, controlling weeds in corn is critical. Yield can be lost just by letting adjacent weeds reach a height of 4 inches or more, so do what you can to ensure weeds never emerge.
4. Apply a preemergence herbicide next spring. In most cases, you can’t manage for higher yields if you don’t have adequate weed control. And if you don’t have adequate weed control from the start, your in-season options may be limited. Should you be applying a fungicide, micronutrient or plant growth regulator? If you have weedy fields, probably not.
Bottom line: If your goal is to optimize yields, you need to control weeds first. Most Minnesota acres have tillage in the fall, and if a burndown is needed, it can be done in the spring as a preemergence application. However, if you’re a no-till or minimal-till farmer, a fall burndown is recommended to put you ahead of the game in the spring.
The best weed control option is to prevent emergence. Start with those foundational layers of residual chemistries and then work up to a spray program with multiple MOAs that will help you manage those all-too-familiar, hard-to-control weeds.
Zuk is a regional agronomist with WinField United in southern Minnesota. Contact him at email@example.com.