By Christie Delfanian

A stem canker forecasting model is in the works for sunflowers. South Dakota State University, North Dakota State University and the University of the Nebraska-Lincoln plant pathologists are working together to develop a model that will help determine when and if a fungicide application may be needed to protect the crop.

“Fungicides can help control stem canker, but timing is critical,” says Febina Mathew, SDSU field crops pathologist. Currently, there is just one fungicide that’s effective, and it has a narrow 10-day application window. If you apply it too early or too late, it doesn’t work.

“How to time the spraying is the million-dollar question,” says Sam Markell, NDSU Extension plant pathologist.

40-50% yield losses
“Phomopsis stem canker is a very serious disease for the sunflower industry,” says Rick Vallery, South Dakota Oilseeds Council executive director. It can cause yield losses of 40-50%

Randy Steiger, who farms in Campbell County, S.D., quit planting sunflowers in 2015 due to lodging and yield losses from the fungal disease. He and his brother Marley used to grow as much as 900 acres of sunflowers.

Cool, wet conditions during and after flowering increase the chance of sunflowers becoming infected. The fungus that causes stem canker overwinters in plant debris. The spores are spread by wind and rain splash. How big the yield losses are depends on how fast the disease spreads.

Borrowing from soybeans
To develop the stem canker forecasting model, Mathew used information technologies originally developed in response to the threat of Asian soybean rust. Mathew is working with professor Scott Isard of Pennsylvania State University, and Roger Magarey, a senior researcher at the North Carolina State University Center for Integrated Pest Management. Their work in conjunction with the precision agriculture company ZedX Inc. has led to the development of the integrated Pest Information Platform for Extension and Education. It allows for sharing of pest observations and pest and disease model outputs nationally.

Six test sites
Last year, the sunflower stem canker forecasting model was tested at six locations — three in South Dakota, two in North Dakota and one in Nebraska. Testing to validate the model will continue in 2018 and 2019. When it is fully vetted, the model will be rolled out as risk maps showing where and when the stem canker risk is high.

“Having this model will allow growers an opportunity to get ahead of the disease and spray at the appropriate time to try to mitigate losses. This will be a very valuable tool,” says John Sandbakken, National Sunflower Association executive director. The risk map will be available on the National Sunflower Association website.

The three-year project is being supported by a $300,000 USDA grant through the Critical Agricultural Research and Extension program

Delfanian is the SDSU research writer.