Tank Mixing for Best Results
Successful farmers use multiple herbicides in every application. Various approaches to tank mixing two or more herbicides that are labeled for your most troublesome weeds can slow down the evolution of resistance.
That’s one of the findings of a recent study by weed scientists at the University of Illinois and the U.S. Department of Agriculture. The following points are among the research findings:
- Mixing is better than rotating. Exposing weeds to multiple effective modes of action simultaneously is a better way to lower selection pressure than rotating herbicides or applying them sequentially. Why? A few plants with natural resistance to a particular mode of action could survive an application of one product containing that mode of action. But if you attack those same weeds with two different modes of action simultaneously, you will kill them instead of selecting for them.
- Your management matters. The study examined over 500 site-years of herbicide application records from central Illinois grain farms. Data from 2004 to 2006 showed that growers who averaged 2.5 modes of action in the tank were 83 times less likely to have resistant waterhemp four to six years later than those who averaged 1.5 modes of action in the tank.
- You shouldn’t stop at the number of modes of action. What matters is the number of effective modes of action. Tank mixing slows weeds’ evolution toward resistance only if each product in the mixture is still capable of killing the target weeds.
- Tank mixing alone is not enough. The study authors noted that “Although measures such as herbicide mixing may delay glyphosate resistance or other herbicide resistance traits, they are unlikely to prevent them,” and stressed that truly diversified management practices were critical for long-term weed management.
These practices include integrated weed management tactics such as:
- weed identification
- crop and trait rotation
- starting with clean fields
- preventing weed seed deposits
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