Challenges posed by glyphosate-resistant weeds are making it clear that long-term weed control must be based on best weed management practices. New data highlights industry expert agreement that herbicide programs with multiple modes of action are essential.

There Are No “Superweeds” – Just Unsustainable Practices

“A ‘superweed’ is a weed that is resistant to an herbicide, and we have been dealing with resistant weeds for more than 50 years,” said Steve Weller, horticulture professor, Purdue University. “Individual plants adapt to any stressor, mechanical or chemical, and gradually become the predominant biotype. Using any single management practice over and over will eventually produce a resistance challenge.”

Recent Field Report of Auxin Resistance Reinforces Need for Several Modes of Action

Resistance to auxin herbicides like 2,4-D has been relatively rare despite six decades of use. However, repeated reuse over an extended period without the intervention of alternate modes of action, tillage or crop rotation can build weed resistance to any class of any herbicide, including auxins. One such case now under study involves a non-crop land production field that received continual treatments of 2,4-D up to twice a year for at least 15 years. These practices resulted in an isolated case of resistant waterhemp, due to this tremendous selection pressure exerted on a single mode of action over a period of many years.

“In looking at this specific field, the importance of multiple modes of action is very clear,” says Greg Kruger, Cropping Systems Specialist, West Central Research & Extension Center, University of Nebraska-Lincoln. “It is unrealistic to expect any herbicide that is used exclusively for this extended period of time to not come under some pressure.”

Multiple Modes of Action Like Adding Several Locks to a Door

Weller likens the best management practice of using multiple modes of action to that of adding a deadbolt to a door that only locks at the knob. “The thief, in this case the weed, might manage to get by one of the locks, but if you have several, as in several modes of action, it is much harder. If you can control a weed with two or three mechanisms of action, the likelihood of resistance occurring to all the mechanisms used is greatly reduced.”

Enlist Weed Control System Designed As Sustainable System

The Enlist Weed Control System under development by Dow AgroSciences will be a new sustainable solution offering several modes of action, centered on glyphosate and a new 2,4-D product that has been reinvented to match the needs of today’s farmers while retaining its trusted and proven efficacy.

The Enlist Weed Control System was designed with resistance management principles in mind. It combines crop herbicide tolerance traits that enable the use of glyphosate, glufosinate, and fop chemistries (depending on the crop) as well as new 2,4-D choline. Accordingly, the Enlist system will exert control against weeds in multiple ways, making it more difficult for weeds to adapt.

Enlist Duo, the Enlist herbicide solution that is a proprietary blend of glyphosate and the new 2,4-D choline, will be part of a program that also recommends foundation herbicides. This approach will provide even more modes of action for the weed control program.

“We understand the challenges posed by resistant weeds, and have designed a system to address them,” said Joe Vertin, Global Leader, Enlist Weed Control System, Dow AgroSciences. “Enlist will partner with and improve the glyphosate system, and our program approach will provide multiple modes of action to give growers the weed control they need.”

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