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Casebook: surfactant slip up

Adding the correct adjuvant to your tank mixture is as important as getting the herbicide tank-mix partners right. Getting it wrong can be a costly mistake, as one producer from Alberta found out last spring.

Two weeks after spraying his wheat crop with a grass and broadleaf herbicide mixture, Jim found healthy wild oats growing in his field. He asked me to visit his 2,000-acre farm east of Fort Saskatchewan, Alta., where he grows wheat, barley and canola, to evaluate the situation. “There must be something wrong with the chemical,” he told me.

In the field, I noticed the broadleaf weeds were being controlled, but the wild oats were showing few to no signs of herbicide activity, with the exception of a touch of yellowing to the leaves. The wild oats were scattered uniformly throughout the field.

Although the incidence of herbicide-resistant weeds has increased in this area over the years, I did not think that was the problem in this field. Jim had taken precautions, such as implementing crop and herbicide rotation strategies, to prevent herbicide resistance on his farm. Herbicide-resistant wild oats usually grow in random patches, and are not found uniformly scattered across the field. We could also eliminate resistance as the issue because some of the (non-herbicide-resistant) wild oats would have been controlled by the herbicide.

Jim told me he had sprayed Group 27 and Group 6 broad-spectrum broadleaf herbicides mixed with a registered Group 1 herbicide for grassy weed control. However, Jim’s sprayer records pointed to an adjuvant slip-up.

When I asked Jim what adjuvant he had added to his tank-mix he said, “This is the one I typically use with my other tank mixes. I always have some on hand.” Jim was referring to a non-ionic surfactant that was not registered for use with the Group 1 herbicide for grassy weed control!

The registered herbicide tank-mix required a specific adjuvant, and not the non-ionic surfactant Jim usually added to his other mixes. Without the registered adjuvant, the Group 1 herbicide lost its effectiveness for controlling grassy weeds.

We still had a window of opportunity to respray Jim’s wheat field with a Group 8 herbicide to control the wild oats. Jim had good results with this herbicide, which stunted the growth of the large wild oat plants and prevented them from heading.

Because he had to respray, it was a costly mistake; however, catching this mistake and correcting it prevented any wild oat runaways that would have carried over to the next year.

Being aware of correct mixing instructions and tank-mix partners, including adjuvants, and the important role they play in herbicide efficacy saves producers time and money. Keeping abreast of the selection and application of chemicals by consulting a crop protection guide, or by picking chemicals with the adjuvant included may also prevent costly mistakes. †

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