Herbicide cross resistance in weeds

With no major new site-of-action herbicide introduced into the marketplace in the last 20 years, the stagnation or decline in available herbicides in the past decade in a number of jurisdictions, and ever-increasing incidence of herbicide-resistant (HR) weeds, more efficient use of our existing herbicide tools will be required to proactively or reactively manage HR weed populations. Herbicide-resistant weed management can be aided by crop cultivars with alternative single or stacked herbicide-resistance traits, such as synthetic auxins, which will become increasingly available to growers in the future. An examination of cross-resistance patterns in HR weed populations may inform proactive or reactive HR weed management through better insights into the potential for HR trait-stacked crops to manage HR weed biotypes as well as identify possible effective alternative herbicide options for growers. Clethodim is the lowest resistance risk acetyl-CoA carboxylase (ACC) inhibiting herbicide, with only two of eleven target-site mutations (amino acid substitutions) in weed populations that confer resistance. However, there are no reduced-risk acetolactate synthase/acetohydroxyacid synthase (ALS/AHAS) herbicides or herbicide classes. Growers will be increasingly reliant on reduced-risk herbicide sites of action (groups), such as microtubule assembly inhibitors (e.g., trifluralin, pendimethalin), synthetic auxins (e.g., 2,4-D, dicamba), some photosystem-II inhibitors (nitriles such as bromoxynil), protoporphyrinogen oxidase (PPO) or hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors, glyphosate, or glutamine synthetase inhibitor (glufosinate), used in sequences, mixtures, or rotations, to manage HR weed populations. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.