FOXHOME, Minn. — Sugarbeet growers have a new weapon against their No. 1 nemesis in recent years, the fungus cercospora.
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.
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.
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.
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.
South to north
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.)
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.
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.
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.
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.
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.
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.
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.