There are many important factors to consider in herbicide resistance management. The Herbicide Resistance Action Committee (HRAC) suggests an integrated weed management plan to help manage resistance. A few of the recommendations include crop rotations, as well as cultural and chemical practices.
According to HRAC, crop rotation is an effective method in helping to delay the onset of herbicide resistance. The principle goal is to avoid planting successive crops which require herbicides with the same chemistry or mode of action (MOA) in the same field year after year. Planting rotational crops also allows for the diversification of herbicides with different MOAs. In addition, crop rotation provides an opportunity to choose crops with different seeding times and seedbed preparation, making it easier to avoid or even disrupt the growth season of the weed. Some suggested crop rotations include row crops after small grains or grain crops after legumes. These examples may be implemented for a two or three-year period or longer.
Cultural weed control methods are non-chemical ways to reduce the soil seed bank and should be incorporated into the weed management strategy. Although not all methods are effective in all situations, some examples of cultural weed control measures include: cultivation prior to seeding, using clean, certified crop seed, and post-harvest grazing. Incorporating several cultural weed control methods into a management plan can help enhance a herbicide’s effectiveness.
Herbicide rotation includes alternating MOAs, or groups, as well as chemistries within each group. While it is critical to rotate products from season to season on a particular field, it’s equally important to choose products with different MOAs as well. Switching between herbicides in the same group or MOA has essentially the same effect as using one herbicide over and over again.
Tankmixes can also be a useful tool in weed resistance management programs. However, for tankmixes to be effective, their active ingredients should provide high levels of control of the target weed and include active ingredients from different modes of action.
Use of burndown herbicides like paraquat (such as Gramoxone Inteon®) or glyphosate (such as Touchdown®) can be an effective practice by eliminating weed flushes prior to crop emergence or during fallow periods which can dramatically reduce the weed seed bank.
Integrated weed management plans that implement crop and chemical rotations can help to ensure herbicides’ maximum effectiveness, and can also help aid in delaying and managing herbicide resistance.
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