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.
- 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:
- Use proactive weed control (pre-plant or pre-emergence) with an herbicide tank mixture or pre-pack having at least one mechanism of action that is known to control the resistant weed.
- Use post-emergence herbicides only in tank mixtures or pre-packs with at least one mechanism of action that is known to control the resistant weed.
- 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.
- 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.
- 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.
- 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
Topics Included in this Module
- Herbicide Resistance Terms to Know — Understand the difference between population shift and resistance as well as other concepts.
- Is Herbicide Resistance to Blame? — Resistance is not the only cause of weed control failure
- Incidence and History of Herbicide Resistance — Resistance to one or more of 25 herbicide families has been observed in the U.S.
- Mechanisms of Herbicide Resistance— How does resistance develop in a population?
- Proactive Herbicide Resistance Management — Methods to help slow or prevent the development of herbicide resistance.
- How to Manage Herbicide Resistance — What you can do if resistance is already a problem
- Herbicide Spraying by the Numbers — Use information on pesticide labels to rotate herbicide “families”
- Resources and Suggested Reading — Additional information about herbicide resistance.