U of I Researchers Target Sugar Beet Disease

University of Idaho researchers have promising leads on management practices and new pesticide options to help the state’s sugar beet farmers get a handle on a fungal disease that’s posing an increasing threat in their fields. 

Cercospora beticola thrives in moist, warm conditions and creates necrotic spots on sugar beet leaves. Plants expend their energy regrowing dead or damaged leaves at the expense of sugar production, resulting in yield losses of up to 40% in susceptible cultivars.

James Woodhall, an associate professor of plant pathology based at the U of I Parma Research and Extension Center, and his graduate student, Hayden Woods, obtained an $18,000 grant through the U.S. Department of Agriculture’s IR-4 Project to evaluate seven different fungicide programs for controlling the disease.

IR-4 develops data for the registration of safe and effective pest management solutions for specialty crops with the U.S. Environmental Protection Agency.

Amalgamated Sugar Co. is conducting separate trials assessing the same fungicide programs.

“This is a sugar beet disease that is gaining importance in Idaho. It just seems to be getting more and more severe,” Woodhall said. “It was first found in Idaho in the 1960s, but it’s slowly getting worse.”

Woodhall believes a combination of factors have contributed to mounting grower headaches from Cercospora beticola.

Changes in irrigation likely play a role, as most farmers have switched from in-furrow irrigation to overhead sprinklers, which moisten leaves and create favorable conditions for spores.

He also suspects the disease is entering the state on growers’ sugar beet seed and is likely over-wintering in infected sugar beet tissue in fields.

Large Cercospora spores don’t travel far but can take hold in adjacent fields and spread slowly from one field to the next.

Perhaps the greatest challenge growers face in managing Cercospora is that it quickly develops resistance to pesticides. Woodhall and Woods have sought to identify new modes of action to include in pesticide programs to avoid the onset of resistance to commonly used products.

“The long-term approach is we need to have resistant varieties,” Woodhall said. “Our near-term approach is we need cultural management and we need additional chemical management options.”

Woodhall and Woods enjoyed good results with a treatment regime that included an application of a fungicide that’s already labeled for sugar beets but not widely used, containing the active ingredient thiophanate-methyl.

The addition of that product contributed to a 67% reduction in disease pressure, compared with a 35% reduction resulting from a comparable program that didn’t include thiophanate-methyl.

They also found two fungicides that aren’t currently labeled for sugar beets that provided strong control against Cercospora beticola.