How to Manage Herbicide Resistance

Glyphosate-resistant marestail (right) and nonresistant marestail stand side by side in an Indiana field. (Photo/Purdue University Department of Botany and Plant Pathology)A publication-quality photograph is available at http://ftp.purdue.edu/pub/uns/bar

Glyphosate-resistant marestail (right) and non-resistant marestail stand side by side in an Indiana field. (Photo/Purdue University Department of Botany and Plant Pathology) A publication-quality photograph is available at http://ftp.purdue.edu/pub/uns/bar

If herbicide resistance is confirmed or highly suspected, diverse approaches to managing herbicide resistance need to be incorporated into weed management strategies immediately for the species in question.

  1. It is best to stop using the herbicide in question and other herbicides with the same mechanism of action. However, in many cases the herbicide continues to work on a large number of weeds and is still the best choice for overall weed control. If the decision is made to continue using the herbicide, there are several options:
    1. Use proactive weed control (pre-plant or pre-emergence) with an herbicide tank mixture or prepack having at least one mechanism of action that is known to control the resistant weed.
    2. Use post-emergence herbicides only in tank mixtures or prepacks with at least one mechanism of action that is known to control the resistant weed.
    3. Do both a. and b.* Any of these options provides at least one additional MOA that will help to prevent further spread of the resistant weed. In addition, other weed control tools should be used to complement the MOA that is still active on the resistant weed so that undue selection pressure is not placed on the additional MOA.
  2. If the resistant weed is confined to relative small areas, take steps to prevent seed production.  If the weed is still small enough to control with other herbicides, treat the affected spots. Alternatively, the weed could be removed by hand, or the crop in infested patches could be sacrificed and the weed controlled by destructive tillage or with the use of a non-selective spot herbicide application. Do not let resistant weeds go to seed.
  3. Avoid moving seed or vegetative propagules to other fields and farms. Use a power washer or compressed air to help remove seed and plant parts from any equipment used in the field. If any fields have a history of herbicide resistant weeds, use farm equipment in those fields last.
  4. Seek advice from the Cooperative Extension Service, your agricultural retailer, crop advisor, and/or University Extension weed specialist to assist in the long term planning of weed control in subsequent crops.

Adhering to the resistance management principles outlined above will help delay or prevent resistance from recurring and prove beneficial in managing resistance the long term.

Compiled by Dr. Wayne Buhler, PhD.

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