Weed Management, PART III: Herbicide Mixing is Best Practice for Mitigating Weed Resistance
This is the third and final article in a three-part series, focusing on how to deal with herbicide-resistant weeds. In the two previous editions of TECHtuesday, we discussed the “how’s and why’s” of herbicide-resistant weeds. To read the two previous articles in the series click below:
This article goes into more detail about planning your weed management practices.
Research conducted in Illinois by Dr. Aaron Hager and his associates revealed, not surprisingly, that management factors are most important when it comes to the occurrence and the severity of resistance.
Dr. Hager’s team also concluded that herbicide mixing, and not herbicide rotation, is the best practice for mitigating weed resistance. Using two herbicides with different sites of action each time you spray for weeds makes it 83 TIMES LESS LIKELY that weed resistance will develop!
The following steps will help you put effective weed management practices in place:
1. Identify your driver weed. Which weed will most likely develop resistance and has, historically, been the most difficult to control in your fields? For most of us in the Upper Midwest, this is Waterhemp. Depending on your geography, however, the driver weed could be Palmer Amaranth, Kochia, Marestail, Ragweed, etc.
2. ALWAYS use a pre-plant or pre-emergence application. Never rely exclusively on post-emergent control options.
3. ALWAYS follow label directions.When applying post-emerge products, make certain you do not exceed the labeled weed height for optimum control.
4. Mix herbicides. Each time you make a herbicide application, use two products with different sites-of action for controlling your driver weed.
» There are many lists available online from universities.
» If you have a weed population that is already resistant to glyphosate, then glyphosate is NOT an effective site-of action product against your driver weed.
» If you are trying to control a broadleaf weed, like Waterhemp, adding a product for volunteer corn does NOT give you an extra site-of-action for the broadleaf weed.
5. Have a plan ready. Remember, selection for herbicide resistance happens every time you make a pass across the field. Make plans now for a comprehensive and sustainable weed management program.
Implementing an effective weed management program is critical to protecting the effectiveness of seed options. Weeds can and will overcome all trait options given enough time. While we all recognize the value of having multiple options for herbicide resistant traits, the end-result will eventually be the same unless we protect against weed escapes now.