MSU Webinar Explores Cercospora Leaf Spot Development, Management

(Left) Cercospora leaf spot on sugarbeet, Tuscola County. (Right) Enlarged photo of lesion illustrating the gray to tan center, dark brown to purple border and black pseudostromata. Photo by Daniel Bublitz.

Sugarbeet growers know that cercospora leaf spot (CLS) is the most damaging foliar disease in the state. The small, circular lesions on the leaves can lead to defoliation and death.

“We can expect losses of up to 40 percent in our sugarbeets and that is both root and sugar yield that’s reduced, but also an increase in impurities and potential storage losses later in the season,” said Jamie Willbur, MSU Extension potato and sugarbeet plant pathologist.

She presented during the MSU Field Crops Virtual Breakfast.

“Conditions that are ideal for infection are relatively warm for a fungal pathogen—65 to 89 degrees Fahrenheit, but it does require a high amount of relative humidity greater than or equal to 90 percent, or free moisture on the leaves for several hours following rain events or morning dew,” said Willbur.

She said management for CLS is a combination of cultural, varietal, and fungicide strategies. This can be done by crop rotation, avoiding planting near fields with CLS, weed management, and choosing the right varieties.

“The host-resistance side, this can be difficult to breed for because there are several genes that are controlling this resistance,” said Willbur. “Historically, good resistance has come at the cost of yield. As a result, no varieties are immune to cercospora leaf spot entirely. However, there are new varieties with a new source of resistance that are available in 2021.”

On June 16, CLS was identified at the MSU Saginaw Research and Extension Center.

“As a comparison, in previous years, the first reports occurred on July 24, 2020—it was a delayed year, so there may have been some spots present before then,” said Willbur. “In 2018 and 2019, it was about mid-June in both of those years, so we’re on track with 2018 and 2019.”

For more information on foliar programs, and fungicide application rates and timing, we have a link to Willbur’s presentation here.

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