New Technology Delivers Resistance Against Cercospora — The ‘No. 1 Production Problem’ In Sugarbeets

By Becca Roberts Last updated Aug 16, 2021

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New sugarbeet seed varieties resistant to cercospora leaf spot disease were commercially available for growers to plant in southern North Dakota and Minnesota in 2021. The improved varieties will save tens of millions of dollars in spray and processing costs and could save hundreds of millions in crop losses.

Mohamed Khan, a professor and Extension sugarbeet specialist for the University of Minnesota and North Dakota State Unviersity, said he expects to see most farmers to adopt the technology in the next three years. He thinks its use in the next two or three years will extend to Michigan, Montana, Nebraska, Colorado and Wyoming.

Sugarbeets are the most prominent specialty crops from southern Minnesota to the Canadian border through the Red River Valley, accounting for some $5 billion in economic activity. But that activity can be hurt by cercospora, which turns green leaves brown, shutting down yield potential.

The new CR+ (cercospora resistance plus performance), from KWS Saat, parent company for Betaseed, commercialized seed for some growers in southern Red River Valley of North Dakota and into southern Minnesota.

This year’s sugar beet crop near Foxhome, Minn., shows potential for a healthy, 30-ton-per-acre yields, but Cercospora leaf spot can quickly cut yields, reduce sugar content from 18% sugar down to 15%, and increase the processing costs of removing impurities. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

German-based genetics company KWS Saat in its website on the topic says about two-thirds of global sugarbeet acreage has a moderate to high cercospora pressure. Cercospora is the most destructive leaf disease of sugarbeets, sometimes cutting crop yield by 50% in some places, the company says on its website.

Khan said the new technology will prolong the usefulness of other fungicide treatment.

“It’s a real game-changer,” he said, describing the technology in a private tour of his cercospora research plots near Foxhome, Minn., about an hour east of Fargo, N.D. The site has a plot tour on Aug. 24, 2021.

Khan manages research/demonstration plots annually of about 25 acres on land farmed by Kevin Etzler of Foxhome. The research is open to the public, usually replicated four times, on a scale similar to typical farm fields. Here, the Minn-Dak Farmers Cooperative of Wahpeton, N.D., and American Crystal Sugar Co., of Moorhead, Minn., evaluate (blind-)“coded” varieties they test for various seed companies to ensure they meet minimum standards for cercospora vulnerability. Much is at stake.

Extension Service sugarbeet specialist Mohammed Khan supervises inoculation and other studies at sugar beet research plots at Foxhome, Minn., helping to evaluate new disease-resistant varieties and fungicide spray regimens. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

Infested fields hit can easily lose 40% of their yield and about 2 to 3 percentage points of sugar — a loss of millions of pounds of sugar and millions of dollars throughout the growing regions.

“You can easily lose $300, $400, $500 per acre,” Khan said.

A primer on the history of cercospora

South to north

University researchers at Foxhome, Minn., test plots inoculate varieties to help study disease resistance and effectiveness of fungicide combinations. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

Since 2016 in the Minnesota/North Dakota region, cercospora has been most prevalent in the two southern co-ops: Minn-Dak Farmers Cooperative and Southern Minnesota Beet Sugar Cooperative. The areas where those co-ops operate generally get more rainfall and heat, which increases yields but also creates more problems with cercospora. Over the past two decades, sugarbeet yields have increased nearly 50%.

Beets are a high investment crop in the three closed cooperatives. Farmers in North Dakota and Minnesota together produce 650,000 acres of beets. Diseased plants can produce 1 trillion spores per acre.

“That’s trillions and trillions of spores are circulating. The larger the number of spores, the more mutations that can lead to fungicide resistance,” Khan said. “We are trying to kill the fungus and the fungus wants to live.”

From 2000 to 2015, farmers got excellent control by applying two to four fungicide applications per year, depending on the farms’ locations.

One fungicide type is the “quinone outside inhibitors” (“QoI”), a fungicide that specifically stops the production of energy. The main QoI for sugarbeets has been “Headline,” a pyraclostrobin (from the strobilurin class of chemistry). Because of its high specific activity, it has been effective against target fungi.

But Headline suddenly became ineffective.

“If you sprayed the field in 2016, and went back to that fields three to four weeks later, it started to turn brown,” Khan said.

The reason? Mutations.

One mutation resulted in complete resistance to the QOI fungicides.

“All the fungus had to do was change an amino acid at one position (in its genes) for another — an alanine changed to guanine,” Khan explained.

And that was that.

At the same time, it developed “reduced sensitivity” to another previously effective fungicide group — triazoles (also called “demetallization inhibitors”). This puts holes in the fungi’s cell membranes.

Khan started recommending using one new fungicide with another mode of action — “especially an older chemistry.” (The older fungicides are “multi-site” types, used since the 1970s.)

Mohammed Khan, a professor and sugar beet specialist for the University of Minnesota and North Dakota State University, uses a battery-powered spore trap to monitor levels of Cercospora leaf spot disease at research plots near Foxhome, Minn. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

The most popular older fungicides were ethylenbisdithiocarbamates. The EBDCs included trade names Mancozeb and Penncozeb. Other old chemistry are known as “tins” — triphenyltin hydroxide (TPTH). The common “coppers” were copper hydroxide and copper oxychloride..

A $200M hit

The 2016 season was the warmest and wettest in the 121-year weather record history for Minnesota. This was good for growing beets but devastating if you had cercospora that had become resistant to the previously most-effective fungicides.

“Because the best modes of action were no longer effective in 2016, our growers lost close to $200 million — less income to producers in North Dakota, Minnesota and Michigan,” Khan said.

From 2016 to 2020, growers in Southern Minnesota applied six to seven fungicide applications per year, always in mixtures, with mixed success, depending on the amount of rain.

A weather station at the sugar beet Cercospora leaf spot research plot near Foxhome, Minn., provides temperature (air and soil), relative humidity and precipitation data that is correlated with a spore trap to help scientists recommend the best way to fight yield- and quality-robbing disease. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

QOI fungicides worked well until years like 2019, when repeated rains washed them off and they had to be reapplied. “The disease will overtake the plants. You will have low yields, very little to harvest,” he said.

In 2020, the southern Minnesota growers had effective disease control — with yields of nearly 30 tons per acre, with 17% sugar. In 2019, Southern Minnesota Beet Sugar Cooperative had reported a yield of 23.4 tons per acre and a sugar content of 15.63%; however, the 2019 season was further challenged by weeds, diseases and poor harvest conditions.

NDSU started urging seed companies to speed up work they already were doing to incorporate tolerance. The new cercospora improvements came through conventional breeding, not genetic modifications. KWS breeders had been finding strong cercospora tolerance in a broad range of wild beets.

Khan and his research team inoculate plots to allow cooperatives to rate sugarbeet varieties for their cercospora leaf spot resistance. He also studies fungicides for their effectiveness, as well how they work in mixes and rotations.

Mike Metzger, vice president of agriculture for Minn-Dak Farmers Cooperative at Wahpeton, N.D., has had the new CR+ varieties in his company’s research plots for two years. He describes cercospora as the co-op’s “No. 1 production problem.”

Metzger said that 60% of seed planted by Minn-Dak Farmers Cooperative at Wahpeton this year were the improved cercospora-resistant sugarbeet varieties. Khan said about 15% of the crop for Southern Minnesota at Renville also also are the new varieties.

All of Minn-Dak’s members this year were offered an opportunity to buy the new seed, and Metzger estimates that 80% to 85% did. The new seed came at about a $40 per acre cost above the typical seed price, which ranges from $200 to $250 an acre.

“It’s going to offset three sprays,” which Metzger and Khan say is at about $25 to $30 per spray.

Mohamed Khan, a North Dakota State University and University of Minnesota sugarbeet specialist, says new ‘improved cercospora leaf resistant” beet varieties were used on 60% of Minn-Dak Farmers Cooperative growers and 15% of Southern Minnesota Beet Sugar Co-op, and should be available to most growers nationwide in two to three years.
Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

Metzger likened the new variety impact to the to “herd immunity” when it comes to COVID-19. Going to resistant varieties could drastically reduce the amount of fungus over a two-or three-year period.

“We don’t have to worry about that massive cercospora cloud hanging over our head. It gives us a chance to take a breath, hit the reset button,” he said.

Khan said the new cercospora-tolerant varieties appear to have tonnage yield comparable to approved sensitive varieties. The sugar concentration may be a little lower.

“But overall, the recoverable sucrose is as good as the other varieties we’ve had,” he said.

In June 2021, researchers inoculated sugar beets in research trials with Cercospora leaf spot disease spores. They were just beginning to show symptoms on July 16, 2021.
Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

He said other seed companies (Crystal Beet Seeds, SESVanderHave, Hilleshog and Maribo) also are working toward commercializing resistant varieties.

While the cercospora-resistant varieties so far have come through conventional breeding, Khan said the industry is looking at developing other traits through genetic modification. Some on the horizon include triple-stack resistance to glyphosate (Roundup) glufosinate (Liberty) and dicamba perhaps in 2025 or 2026. The only sugarbeet GMOs now approved for use are for Roundup (glyphosate) resistance.

Mohammed Khan, a University of Minnesota and North Dakota State University extension sugar beet specialist, pores through charts that show the effect and timing of different mixes and timing for fungicides to fight Cercospora leaf spot disease. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

Khan and his technicians in late June intentionally inoculate the entire site with cercospora leaf spot disease, accumulated from infected leaves from growers’ fields the previous year, mixed with a talcum powder.

Also, Khan’s larger job is to determine which fungicides are effective in combatting the disease.

The researchers apply the fungicides in applications in 10- to 14-day intervals (depending on rainfall) — about five to six applications across the entire season from late June into September. Khan applies the combinations to beets with varying levels of cercospora resistance. Those include varieties more susceptible than the “conventional, susceptible” growers would normally use.

“If something is working in my research site, it will work in a grower’s field,” he said.

Sugar beet research at Foxhome, Minn., includes a “spore trap.” It uses a vacuum to pull Cercospora leaf spot spores. The spores stick to a sticky tape, moving in a one-week cycle. Researchers have found they’re most prevalent between 5:30 a.m. and 8 a.m. Data from the study should improve fungicide timing. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek.

Part of Khan’s research is using fungicides with the improved varieties to see if he can reduce the fungicide applications and still get high yields. In some of the improved varieties he thinks he can use as few as one — or zero — applications in some years.

In the end, the samples are analyzed at an American Crystal Sugar Co. tare laboratory at East Grand Forks, Minn.

“We do calendar sprays — for growers who don’t want to scout,” he said. “If they they want good yields, they’ll probably have to spray every 10 to 14 days.”

Cercospora first attacks the oldest leaves, which produce the most sugar. The disease doesn’t hit younger leaves until late in the season. Those who scout do so based on leaf spots and daily infection values, some relying on scouts or consultants to determine disease severity and the best time to apply fungicides.

Mohamed Khan’s conducts Cercospora leaf spot research on a 25 acre cercospora leaf plot at Foxhome, Minn., on parts of the Kevin Etzler farm. Photo taken July 16, 2021, at Foxhome, Minn. Mikkel Pates / Agweek

In a related study at the research plots, Khan is working with drones to aerially collect images to determine the amount of “brownness” that would indicate an infestation. That will be correlated to infestation data on the ground, and eventually cut the time and cost of scouting fields.

If the drone technology proves itself, Khan is working with an engineering colleague at NDSU to develop a sensor for agriculture that is also usable for detecting weeds in sugarbeets and other crops.ShareBecca Roberts 1268 Posts 0 Comments