Resistance Management Needs
 to be a Part of Pest Control Plan

Twenty years ago there was little attention given to resistance management. Today, that way of thinking has all changed. Crop producers need to know not only what herbicide they are using but also what is its chemical family and the mode of action by which it kills weeds. Using a herbicide with the same mode of action over a period of years on the same field will result in the proliferation of weed genotypes resistant to that mode of action.

Is talk about weed resistance simply an over reaction to a potential problem? If you think so, then consider this:

• Already in Wisconsin there is documented resistance of large crabgrass and giant foxtail to lipid synthesis inhibitors (e.g. Poast, Assure, Fusilade)
• Thirteen states have reported at least one weed species resistant to ALS inhibitors (e.g. Accent, Basis, Broadstrike, Classic, Concert, Exceed, Permit, Pinnacle, and Pursuit)
•  Australia now reports two cases of plant species resistant to glyphosate (Roundup) from fields where that chemical was used repeatedly over a number of years.
• Nearly every crop field in Wisconsin probably has some broadleaf weeds resistant to atrazine.

Many of the new chemicals on the market are ALS inhibitors. Herbicides in this category can be used on a variety of different crops. For this reason, producers need to be aware of what chemical mode of action is being used on each field for each year and take steps to avoid herbicide resistance. These steps would include rotating herbicide modes of action, rotating crops, using mechanical weed control methods, and scouting fields for potential resistant weed species.

This same principle will need to be applied to insect resistance and the use of Bt corn. Planting all corn acres to Bt will eventually result in the proliferation of European corn borers that are resistant to Bt. This is the basis for the recommendation of planting at least 20% of your corn acres to non-Bt hybrids.