Herbicide Resistance (AGR-6)
         

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In recent years herbicide resistance has become an important issue to consider when making weed management decisions. Crops traditionally susceptible to some herbicides are being developed which are tolerant (i.e. resistant) to specific herbicides. For example, corn hybrids resistant to imidazolinone type herbicides, such as Lightning, are now available to producers.

On the other hand, herbicide resistance can occur and develop from natural weed populations. For example, resistance of smooth pigweed to triazine type herbicides (i.e. Atrazine and Princep) has been found and documented in some localized areas of Kentucky where corn is grown in consecutive years. Other states have also reported weed resistance in field crops following the continuous use of certain herbicides. The potential for weed resistance to develop increases with a continuous use of herbicides that have the same mode of action (i.e. similar chemistry). Therefore, herbicide use should be monitored and production practices implemented to prevent and reduce the potential for weed resistance to occur

A key to avoiding development of herbicide resistant weed populations is prevention. Listed below are management strategies to consider in preventing and dealing with herbicide resistant weeds.

  • Scout fields regularly and identify weeds present.  Respond quickly to shifts in weed populations to restrict spread of weeds.

  • Select a herbicide based on weeds present and use a herbicide only when necessary.

  • Rotate crops. Crop rotation helps disrupt weed cycles and some weed problems are more easily managed in some crops than others.

  • Rotate herbicides. Avoid using the same herbicide or another herbicide with the same mode of action (i.e. herbicides that inhibit the same process in target weeds) for two consecutive years in a field. It is possible for a herbicide used in one crop to have the same mode of action as a different herbicide used in another crop. For example, Accent, Basis, Beacon, Classic, Exceed, Harmony Extra, Lightning, Scepter, Permit, Pursuit, Spirit, Python, and Synchrony "STS" contain active ingredients with the same mode of activity in plants (i.e. these herbicides are ALS/AHAS inhibitors).

  • Apply herbicides with different modes of action as a tank mixture or sequential application during the same season.

  • Combine other weed control practices such as cultivation with herbicide treatments where soil erosion potential is minimized.

  • Clean tillage and harvest equipment to avoid moving weed problems from one field to the next.

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For problems, questions, or permission to reprint information from this website, please contact Mike Marshall. Last Update: 12/11/03.