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Managing Phomopsis Stem Canker

Properly identifying and managing Phomopsis stem canker in sunflowers is crucial.

Phomopsis stem canker, which is caused by the fungus Phomopsis helianthi, is a sunflower disease Markell is concerned about. “This one has really blown up on us in the last five or six years. Mid-season, you’ll see brown lesions on the stems, and they hollow out the plant. Usually, you get pretty horrific lodging if you have some wind,” he says Dr. Sam Markel, Professor and Extension Plant Pathologist at North Dakota State University.

Disease incidence has dramatically increased in North Dakota and Minnesota, especially under wet conditions.

Often symptoms begin with lesions at the leaf edges where Phomopsis spores have infected the plant. The dark brown lesions spread into the stem, eventually hollowing it out.

Managing Phomopsis stem canker is crucial. Choosing hybrids with resistance or tolerance to the disease is important, but not a perfect solution. Some hybrids manage the disease better than others, says Markell. If producers have had Phomopsis stem canker in the recent past, he recommends they plant hybrids with some level of resistance or tolerance to the pathogen.

Presently, Markell is working on managing this disease better with fungicides. “Fungicides are not a perfect solution, but we’ve been doing a lot of research on this for some time and in some environments, fungicides may be helpful,” he says. “We’re looking at the combination of growth stage and chemicals.”

Studies included the strobilurin (Headline), triazole (Folicur) and succinate dehydrogenase inhibitor (Endura®) fungicide classes. In each of the trials, better yields, lower numbers of wilted plants and a higher percentage of robust heads were associated with strobilurin application at R1, says Markell.

However, he’s not recommending this strategy to producers just yet because study results have been variable and somewhat inconsistent, he says. “We couldn’t hit the timing right. We think it’s because that infection window is so wide. But if it’s wet right before R1, and the conditions are favorable for Phomopsis, this is something growers might want to consider.”

In the future, a forecasting model will be available to help growers with fungicide application decisions for Phomopsis stem canker management. “We’re developing a forecasting model right now that’s being led at South Dakota State University. Hopefully in a couple of years we’ll have that available,” says Markell.

Phomopsis Stem Canker
NDSU Sunflower Disease Diagnostic Series

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