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How to mix herbicides and fungicides

Follow label recommendations, do your own “jar test,” apply products at your own risk, and call the chemical companies for any advice they might have. Those are about the four main pieces of advice for farmers thinking about tank mixing herbicides and fungicides for a one pass application this year.

Not a lot of research has been done in Canada on the practice of tank mixing the two types of pesticides, so most of advice on the topic comes from the pesticide manufacturers. What works? What doesn’t work? Is there any harm? Is the dual treatment effective? Those are questions that need to be asked.

The convenience of tank mixing products to control weeds and disease all in one spray application is obvious. But how well does it work?

Points to keep in mind

  1. There are a few registered herbicide/fungicide tank mixes that appear on product labels. Syngenta, for example, has a registered tank mix for Horizon herbicide and Tilt fungicide. Bayer CropScience has a unique three-way registered tank mix with Stratego fungicide and Puma Super and Refine Extra herbicides. The registered tank mixes can generally be regarded as safe to use.
  2. In other cases there are herbicides registered for use on peas or wheat for example and there are fungicides registered for use on peas or wheat, but the two products are not registered for combined or tank-mix use. Since the two products are registered for their specific use, it is not illegal for farmers to tank mix them to make a single application, but they do so at their own risk. The chemical manufacturers are not liable if one or both products don’t work, or there is crop injury.
  3. If you are thinking about tank mixing two products that are registered for separate use only, do a jar test first. Mix the fungicide with the herbicide with some water in a clear jar and see what happens. If one product happens to settle out in the jar, for example, you can probably expect the same thing to happen in the sprayer tank.
  4. By all means call the chemical company or companies first to see if they have any knowledge or experience on tank mixing the two products even if they are not registered. A lot of companies do their own research and development and have made observations on how tank mixed products react and perform. Some companies are willing to share that information. Call your local representative or the company 1-800 numbers.
  5. Just because products are registered or the tank mix is registered, doesn’t mean that a one-pass application will be effective. Generally, the tank mix is being applied at the optimum time for weed control, and researchers say that is not always the optimum time for disease control. Controlling weeds at the two, three, or four leaf crop stage is often too early for effective control of the diseases, which may not really appear for a few more weeks.

The timing factor

Timing of application concerns two Agriculture and Agri-Food Canada plant pathologists. “I understand the convenience factor,” says Kelly Turkington, who is based at Lacombe, Alta.

But the key to maintaining and protecting crop yield is to protect the top three leaves of the plant, which includes the flag leaf and the penultimate leaf. So while a dual treatment made at the two- or three-leaf crop stage may control weeds, a second fungicide treatment may be needed to protect the flag leaf later on, Turkington says. He and Neil Harker, a weed specialist at the Lacombe centre, have a study underway this year looking at the effectiveness of a one-pass herbicide/fungicide tank mix at both the early weed and late weed stage.

In Saskatchewan, Randy Kutcher, plant pathologist, points out that little research has been done in this area. However, his own limited field trials in the Melfort area over the past five years show little or no response from an early application (three leaf stage) of Tilt. “Usually at that stage there is little or no disease like tan spot present and if it is present on some of the lower leaves, often the crop just grows out of it,” he says. “The two or three times we have done the early Tilt trials we have seen no measurable benefit in yield. That’s not to say other parts of the Prairies might have a different experience.”

Company perspective

Stick with label recommendations is what Lauren Davis, portfolio manager with Bayer CropScience in Calgary, advises. Bayer’s three-way tank mix registration includes Stratego with Puma Super and Refine Extra for both wheat and barley and also Stratego with Puma Super and Buctril M for wheat.

“We promote early disease clean up to maintain a healthy green crop,” says Davis. “Applying the tank mix product at the three to four leaf stage will provide effective control of weeds and any of the early diseases. You do need to protect the flag leaf, so we also recommend regular field scouting as the season progresses. If there is sign of disease then a second application with a product such as Folicur will control a wide range of leaf diseases as well as provide suppression of fusarium head blight.”

Meanwhile, Ed Thiessen, technical crop manager with Syngenta says if there isn’t a label registration for a tank mix, producers should always check with the chemical companies first before trying anything on their own. “Our policy here is to share what we know with producers,” says Thiessen. “In some of our research and development work we have tried different chemical combinations to see how they perform and we can share that knowledge with producers.

“We make it clear that if they try a tank mix combination that doesn’t have a label registration they do it at their own risk,” he says. “I strongly urge producers to call their chemical companies before trying anything.”

— Lee Hart is field editor of Grainews, based in Calgary. Contact him at 403-592-1964 or by e-mail.

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.



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