New Information Listed On Herbicide Labels

New Information Listed On Herbicide Labels

Herbicide labels now include a standardized system to inform users of the product's mechanism of action or MOA. An information box labeled 'Herbicide Group' is present near the top of the label.

Herbicide labels now include a standardized system to inform users of the product's mechanism of action or MOA. Printed on the labels you'll see an information box that is titled 'Herbicide Group' and this box is present near the top of the label. The number in the box represents the MOA of the active ingredient, based on a system developed by the Weed Science Society of America. Premixes containing more than one mode of action will have multiple numbers listed.

Bob Hartzler, an Iowa State University Extension weed management specialist, says the intent of this information is to simplify development of herbicide programs that reduce the likelihood of selecting herbicide resistant weeds. In crop production systems that are relying largely on herbicides for weed management, using herbicides with different MOAs is the primary means of managing resistance.

Generally, the greater number of MOAs used, the less selection pressure placed on weeds, says Hartzler. However, designing an integrated weed control program for your farming operation is not as simple as randomly adding MOAs. "The different MOAs used in the program must have good activity on the important weeds in the field to successfully reduce selection pressure," he says.

Putting together a weed control program for your farm

Following are a few examples where the inclusion of an herbicide in a system relying on glyphosate in Roundup Ready crops would provide little benefit in terms of managing resistance for specific weeds.

• A Group 2 herbicide would provide little benefit for waterhemp since most waterhemp is resistant to these herbicides.

• A Group 15 herbicide would provide little benefit for giant ragweed or other large-seeded broadleaves due to its poor activity on these weeds.

• Tank-mixing low rates (less than 0.75 lbs) of atrazine (Group 5) with glyphosate or other herbicides would provide little benefit.

The new labeling system eliminates the need for farmers, consultants and suppliers to learn the MOA of all the active ingredients used in Iowa agriculture. However, to use the information properly, users must still know the activity of the individual herbicides on the weeds present in the field to insure that the target weeds are being affected by multiple MOAs.

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