Fungicide tank-mixtures with sugar beet herbicides: What are the risks?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

As we are on the front edge of the fungicide applications for Rhizoctonia management in sugar beets, many of these applications often coincide with herbicide applications for weed control. While tank-mixing these two pest management practices could save extra trips across the field, there are some risks associated with tank-mixing certain herbicide programs with fungicides.

Quadris with micro-rate or standard split herbicide programs

Quadris is the most commonly used fungicide for Rhizoctonia management in Michigan. When Quadris is applied with Betamix or Progress micro-rate herbicide programs excessive sugar beet injury occurs. The methylated seed oil (MSO) component used in the micro-rate herbicide program “heats up” Quadris leading to injury. Some may think that the use of a different adjuvant in the micro-rate may reduce this risk. This approach may work, however then the micro-rate herbicide program is not effective for weed control. The best way to get both weed control and Rhizoctonia management is to apply the fungicide and micro-rate herbicide programs separately. From MSU research, our general recommendations are for Michigan growers to apply Quadris or any other fungicide for Rhizoctonia management no less than three days prior to or three days after a micro-rate herbicide application to avoid sugar beet injury.

What about tank-mixing fungicides with standard split herbicide programs? Most of our research has shown that Quadris can be tank-mixed with a Betamix standard split program without severe sugar beet injury. However, in our plots and in growers’ fields there have been reports of sugar beet injury (leaf burn) from tank-mix applications of Quadris and a Progress standard split herbicide program. Again the best way to avoid this injury is to apply the fungicide and herbicide programs separately.

Fungicides with glyphosate in Roundup Ready sugar beets

While we have more extensive data on fungicide tank-mixtures with conventional herbicide programs in sugar beets, last year we conducted a study where we wanted to determine if there would be any injury or sugar beet yield loss from tank-mixtures of glyphosate (Roundup OriginalMax) with different fungicides. We applied glyphosate alone and tank-mixed with Quadris, Gem, and Headline when sugar beets were at the 2- and 6-leaf stages. Very little injury was observed from these mixtures. However, if we added Dual Magnum or Outlook to the glyphosate plus Quadris tank-mixture injury was 31 percent and 13 percent respectively, seven days after application. The injury was mostly leaf necrosis (burning) and the beets quickly recovered. We also looked at combinations of glyphosate with fungicides typically used for Cercospora leaf spot management. At the time of a typical fungicide application for Cercospora (55 DSVs), we applied glyphosate with Copper Sulfate (Champ II), Penncozeb, Eminent, Gem, Headline, SuperTin and Topsin M plus Penncozeb. We did not observe any sugar beet injury from these treatments. Yield was not reduced in any of the treatments as compared with glyphosate alone treatment. So from one year’s research, we found that glyphosate could be tank-mixed with fungicides. However, Dual Magnum or Outlook should not be added to these combinations or injury may occur. Even though glyphosate can be tank-mixed with a fungicide without causing sugar beet injury, differences in nozzle types and application timings may affect both disease and weed control. Caution should be taken in matching up the correct application methods and timings.

Dr. Sprague’s work is funded in part by MSU‘s AgBioResearch.

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