Managing Resistance Before Resistance Manages You
Western Canadian farmers continue to benefit from tools such as glyphosate for non-crop weed control practices including pre-seed, chemfallow and post-harvest herbicide applications. Those applications are an important tool in reducing weed competition for moisture and nutrients, and – particularly for pre-seed applications – can help guarantee the best start for a new crop.
But in recent years, growers have seen an increase in the number of documented cases of weed resistance in Western Canada, proving glyphosate alone can no longer do the job. Researchers now suggest that mixing herbicides with multiple modes of action and using them in the same spray will go a long way in helping to control glyphosate-resistant weeds, and preventing new herbicide-resistant weeds from developing.
Weeds become resistant when they’ve had too much of a good thing. Practices and crops that work well one year are less effective in consecutive years, if there’s no break in routine. That’s why healthy rotation – of crop types, practices and herbicides – is essential.
It’s becoming increasingly clear that using glyphosate alone will not control glyphosate-resistant kochia and may increase the risk of glyphosate- resistance occurring in other weed species in the future. With the emergence of Roundup Ready® volunteers, as well as hard-to-kill weeds that are not controlled by glyphosate alone, growers have found that including an add-in helps to control these weeds and manage resistance.
Ideally, any healthy field will have a rotation of at least three crop types. Research suggests it is equally important to incorporate a host of other natural methods of weed control such as higher seeding rates, the use of clean seed, mowing out suspected resistant weed patches before they go to seed and using herbicides according to label directions.
Herbicides are categorized into 17 different groups according to how they target a weed. For example, Sulfonylurea (member of Group 2) herbicides control weeds by inhibiting the enzyme acetolactate synthase, which is essential to their growth.
“If at all possible, producers should use mixtures of herbicides that use multiple modes of action in the seeding year,” says Ken Sapsford, University of Saskatchewan. “It’s one further step to help stop resistance from developing.”
Group 2 herbicides are a highly effective way to control weeds – but like other herbicide groups they need to be used appropriately, and utilized with herbicides from other groups in the same spray to help manage resistance.
Effective Non-crop Use of Group 2 Herbicides
Pre-seed weed control is a practice that began in cereal crops, and is increasingly popular as an increasing number of Western Canadian farmers adopt minimum tillage practices.
In spring, particularly if the crop rotation included a crop such as RR canola, DuPont scientists recommend a pre-plant/burndown herbicide treatment as an add-in with glyphosate to take advantage of multiple modes of action. Because both Group 2 and Group 9 herbicides have activity on many of the same weeds, growers automatically get multiple modes of action where they need it most. In certain areas, adding a third mode of action such as dicamba, 2,4-D or MCPA (Group 4) is advisable, and can be recommended by an agronomist.
“We know that if we control those weeds early with a burn-off and then come in and seed, controlling those weeds and conserving moisture is the best option,” says Ken Sapsford, University of Saskatchewan.
The Race Is On
The race is on among the world’s leading crop protection companies to tackle the development of weed resistance, and DuPont Crop Protection is committed to working with growers and retailers on solutions that protect the use of all the best tools.
DuPont will continue to promote the use of multiple modes of action in a single spray, because it is an effective way to control problem weeds. DuPont is also committed to designing single and multiple active ingredient products with efficacious use rates and realistic performance claims – and DuPont is nimble enough to meet specific field needs and adjust recommendations based on what’s going on in the field.
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