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Herbicide Resistance: No Déjà vu

Posted by Joan Campbell, University of Idaho | April 8, 2020

When the first group 1 (ACCase inhibitors) herbicide, diclofop (Hoelon), was introduced about four decades ago, wild oat control in cereals was the driver. Along with wild oat control came the benefit of excellent control of Italian ryegrass. Hoelon soon was registered in pulse crops at which point it could be sprayed on every crop in a 3-year winter wheat, spring cereal, spring pulse rotation.

Italian Ryegrass.

About 7 years after its introduction, Italian ryegrass populations were identified with resistance to Hoelon. Heavy selection pressure with continuous use contributed to resistant populations. Other Group 1 herbicides (e.g. Assure II, Poast, Puma, Discover, Achieve) and Group 2 (ALS inhibitors) herbicides followed (e.g. Amber, Osprey, PowerFlex). Over the past four decades, herbicides for Italian ryegrass control have come and gone. Some Italian ryegrass populations developed resistance in a few short years.

The introduction of pyroxasulfone (Anthem Flex and Zidua) for use on wheat certainly was welcome relief after control of Italian ryegrass populations succumbed to several group 1 and 2 herbicides. Pyroxasulfone is a Group 15 (Very-long-chain fatty acid synthesis inhibitors) herbicide, like flufenacet (Axiom), but populations resistant to flufenacet are still controlled with pyroxasulfone. They have a similar mode of action although the chemical families differ.

Pulse crops are now labeled for pyroxasulfone (Anthem Flex) use. This brings us around to all crops in a winter wheat, spring wheat, pulse crop rotation able to be sprayed. Drew Lyon has written about this situation in on the Small Grains site titled, “A Word of Caution About Two New Weed Control Technologies.” Pyroxasulfone is another tool that can be used, but resistance management must be key. The split rate in lentils allows for a high amount of pyroxasulfone. In this case, consider using an alternative herbicide in the following winter wheat crop.

Herbicide Resistance in pulse crops.

No pyroxasulfone resistant weed populations have been reported as of today. Cross resistance between pyroxasulfone and flufenacet has not been seen, but there is no guarantee these won’t happen.

One thought on "Herbicide Resistance: No Déjà vu"

  1. Gregory Dahl says:

    Wise advice! Thanks for sharing.

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