Spraying By The Numbers

Use information on pesticide labels to rotate herbicide ‘families.’

Herbicides are grouped according to family, such as triazines, and by the target site of action or mechanism of action, such as acetolactate synthase or ALS inhibitors. Herbicides within a family have similar chemical structures and, typically, the same site or mechanism of action (MOA). Knowing the chemical family and MOA group to which a herbicide belongs and knowing what other herbicides have the same MOA is critical for creating a plan to prevent or delay development of herbicide resistance.

Screen Shot 2015-05-01 at 1.46.29 AMLook For The Number

To help ensure standardization, the Environmental Protection Agency requested that manufacturers include a pesticide’s MOA group number in a standard format on the label. Herbicides with the same MOA are assigned the same group number. When a premix label displays the group number or numbers, the user can easily determine the mechanisms of action included in the premix.

If a label does not contain a group number, it may be listed in the North Carolina Agricultural Chemicals Manual, which can be found at www.pesticidestewardship.org/resistance/Herbicide/ Documents/ACMHerbiMOA.pdf, by the herbicide name or common name.

Read, Follow The Complete Label

In addition to considering MOA group numbers in the selection of herbicides, review all resistance management recommendations printed on the herbicide label. This may include information on the best management practices for a particular product, target species of most concern and the maximum number of consecutive applications that should be made before rotating to products containing herbicides with different group numbers.

Weed scientists from various herbicide manufacturers have formed the Herbicide Resistance Action Committee (HRAC) to develop uniform resistance management guidelines that can be implemented across geographic regions and across groups of products. Visit HRAC’s website at www.hracglobal.com.

Reduce herbicide-resistant weed selection using proactive resistance management by:
1) Selecting and using herbicides correctly
2) Recognizing weed characteristics that
promote resistance
3) Managing fields, farms, or sites wisely.

For more information on resistance management and other pesticide-related information, go to the Pesticide Environmental Stewardship (PES) website at www.pesticidestewardship.org. The PES promotes the proper use and handling of pesticides and is supported by the Center for Integrated Pest Management.

Herbicide Resistance Management Tips:
• Rotate herbicides with different mechanisms of action, not just different label names.
• Avoid consecutive applications of the same herbicide unless it is used in a tankmix or prepack containing a herbicide with a different mechanism of action.
• Use other weed management options such as cultivation and cultural methods.
• Make sure herbicides are active against the target weed.
• Apply herbicides evenly and accurately, and use labeled application rates.
• Use postemergence herbicides only in tankmixes or prepacks with at least one mechanism of action that is known to control the resistant weed.


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