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Weed Resistance Management | Herbicides with Multiple Actives

Weed resistance management is a serious issue for growers today. Resistance can threaten the long-term viability of any herbicide option. It’s important for growers to protect these tools. Research shows that growers should use products that have multiple modes of action within a single spray.

This advice comes from the latest weed resistance research including a study by Dr. Hugh Beckie, an Agriculture and Agri-Food Canada researcher based at the Saskatoon Research Centre. The study was the result of a four-year project in Saskatchewan and was published in the Weed Science Society of America journal, Weed Technology.

Use products with multiple modes of action in one spray

“The best thing is to have multiple modes of action within a single spray,” says Beckie. “Appropriate mixtures can more effectively delay resistance than just rotating modes of action from year to year.”

“If at all possible, producers should use mixtures of herbicides that use multiple modes of action in the seeding year,” says Ken Sapsford, research assistant at the University of Saskatchewan. “It’s one further step to help stop resistance from developing.”

DuPont™ Express® SG herbicide: Good resistance management tool

Sapsford says that DuPont™ Express® SG , the popular out-of-crop herbicide, fits well with Beckie’s recommendations. “Express® SG will hit a number of weeds on the label with two modes of action when it's tank-mixed with glyphosate,” he says.

Express® SG and Express® PRO are both systemic, Group-2 herbicides.  Because they are always tank-mixed with glyphosate (a Group 9) and both have activity on many of the same weeds, you automatically get the multiple modes of action that Beckie recommends.

The Express® brands significantly improve control of tough weeds such as dandelion and narrow-leaved hawk’s beard in a pre-seed burn-off or post-harvest burndown. Not only will growers improve their weed control but they will also be hitting weeds with actives from two different groups to help manage weed resistance.

Harvested weed seeds and tested for resistance

In the study, Beckie and his team looked at the control of stinkweed averaged over a four-year period from 2004 to 2007 at sites near Watrous and North Battleford, Saskatchewan. They measured weed control (seedling density) and the biomass of the weeds at maturity. They also harvested the weed seeds each year and tested them for resistance, as well as the weed seeds in the soil seed bank at the end of the study.

They used ethametsulfuron, a Group 2 ALS-inhibitor herbicide, applied in rotation with a bromoxynil/MCPA formulated herbicide. Ethametsulfuron was applied one, two, three and four times in the four years. Bromoxynil/MCPA was used in the crop year when ethametsulfuron wasn’t applied.

After one application of ethametsulfuron, weed control was only marginally reduced. But control started to slip quickly each subsequent application to a low of 30 per cent after four consecutive applications.

This was compared to a plot sprayed with ethametsulfuron and bromoxynil/MCPA mixed together. In the plots treated with the mixture, which had two modes of action, the level of resistance basically remained unchanged.

Other DuPont herbicides make good resistance management choices too

DuPont has taken this research seriously and built an excellent portfolio of broadleaf products that have multiple modes of action within a single spray. DuPont™ Barricade® II , DuPont™ Refine® MTriton® C , and Triton® K all have a Group 2 component but also contain other groups that have activity on the same weeds.

It’s important to get two herbicide groups in a single application. To do this effectively, talk to your retailer. They can help make sure you’re maximizing your weed resistance management strategy.

The information provided on this website is for reference only. Always refer to the product labels for complete details and directions for use.