Healthy sugarbeet

In this June 28 photo in Swift County, the sugarbeet is free of disease, but its rain/wind-tattered leaves provide entry points for Cercospora leaf spot (CLS) disease spores. Damp soil conditions are perfect for CLS to thrive. SMBSC growers work hard to keep CLS at bay through fungicide treatments and a variety of best management practices. Photo by Andrea Johnson.

RENVILLE, Minn. – Sugarbeet growing conditions have been excellent in the Southern Minnesota Beet Sugar Cooperative (SMBSC) region.

With the potential, in 2020, to harvest sugarbeets with high sugar content and good tonnage, SMBSC shareholders are taking steps to protect their beets from the devastating disease they fight – Cercospora leaf spot (CLS).

This fungal disease can cut recoverable sugar significantly if left unchecked.

First extensively studied in the SMBSC region in the early 1980s, CLS thrives in the same growing conditions as sugarbeets.

Importantly, the fugus also mutates easily resulting in resistance to some fungicides.

“SMBSC fights at the front lines of the battle with CLS both literally and figuratively,” said Steve Roehl, SMBSC Ag Strategy Manager.

“Our geography and topography are ideal for both micro and macro climates that are especially conducive for CLS infections,” he continued, during a July 2 interview.

“Additional fungicide applications – that are required to prevent the disease and raise a profitable sugarbeet crop – also provide for increased selection pressure that can lead to the development of resistant strains of the fungus to some of our foliar fungicide families.”

To put the brakes on CLS, as well as other sugarbeet diseases and fungicide resistance, SMBSC’s 500-plus shareholders practice a wide range of best management practices (BMP).

For instance, sugarbeets are planted no sooner than every third year, and in most cases are only planted once every 4-5 years in a field.

Cultivars are bred with disease resistance. Growers plant treated sugarbeet seed as early as possible, and weeds are strictly controlled.

Fungicides also play an important role in fighting CLS. The cooperative is continually testing fungicides for their various properties and ability to prevent or cure this disease. Spraying methods – whether by ground rig or aerial – are also studied for maximum efficacy.

Some fungicide testing is conducted in cooperation with Minnesota and North Dakota’s two other sugarbeet cooperatives – Minn-Dak Farmers Cooperative in Wahpeton, N.D., and American Crystal Sugar in Moorhead, Minn. The Sugarbeet

Research and Education Board of Minnesota and North Dakota is a jointly-funded research entity that supports all sugarbeet production in the area.

But, due to the conducive CLS environment and historic infection levels in their growing area, much of SMBSC’s research is conducted in-house for SMBSC alone.

The three cooperatives are all located within a 400-mile stretch, but growing conditions vary enough that BMP’s are not all the same across Minnesota and North Dakota.

Growers discovered, in 2016, that strobilurin fungicides were useless against CLS in the SMBSC region.

“It’s like pouring water on the plant,” said Todd Geselius, SMBSC Vice President of Agriculture, during a phone call. “We do not use any strobilurin fungicides for CLS in any of our treatments.”

Now the SMBSC region has only three or four other modes of action available to defeat CLS.

New in 2020, the cooperative asked growers to apply an Application 0 in June. SMBSC recommended an early pre-canopy-closure application of EBDC when coverage of the lower canopy leaves was relatively unimpeded. This was the only application where the cooperative endorsed the use of EBDC (Mancozeb) alone along with a shortened respray interval.

Then, once growers assume their regular spray application program, they are asked to spray every 10-12 days and to apply a tank mix of two modes of action per application. Growers are also asked to avoid the application of certain chemistries of concern in back-to-back sequences.

The new practice of Application 0 was based in part on a 1982 paper entitled, “Epidemiology of Cercospora Leafspot. W.W. Shane and P.S. Teng. University of Minnesota Department of Plant Pathology.” It was published in the Sugarbeet Research and Extension reports that year.

Shane and Teng discussed the limitations of using a visual rating scale (called the KWS) to monitor early infections of CLS by saying, “The KWS category 1 (the lowest category rating of the KWS scale) covers a wide range of severities from approximately 0.05 to 0.50 percent. For example, the early stages of an epidemic observed in 1982 would not be shown by KWS ratings.”

Roehl points out that this research warned that an epidemic level of CLS inoculum – and that occurred in 2016 and 2018 – could be invisible to the naked eye early in the growing season.

Armed with this information, in 2019, a group of 35 SMBSC shareholders provided detailed accounts of their CLS fungicide program and techniques.

They wanted to see if they could uncover specific inputs or practices with potential for providing CLS disease control at economically acceptable levels in SMBSC production fields.

“When the SMBSC shareholder database looked at the impact of program initiation on revenue per acre and CLS Rating, the data strongly suggested that those who initiated the CLS program early had the lowest CLS score and correspondingly highest revenue per acre,” wrote Roehl in a cooperative newsletter, “presumably by getting out in front of the disease inoculum versus allowing the disease to obtain a foothold in fields,” he added later.

Applying fungicides is time consuming and expensive, and growers wouldn't do it if they didn’t have to – but following the fungicide protocol outlined by cooperative agronomists results in a significant increase in recoverable sugar.

The fungicides offer the potential for profit – especially in 2020 when the crop looks so good. That’s quite different from the scenario during the last two years when growers dealt with wet and cold conditions.

Having studied decades of fungicide research, Roehl has offered sugarbeet growers a carrot if early and proactive fungal treatments do their work. If things look great in August, there is the potential that latter treatments can be extended or that they won’t be needed at all.

“Essentially, the goal is for exquisite control from mid- to late June through the end of August,” said Roehl. “It calculates out to 65-70 days of control for CLS.”

This article clarifies Southern Minnesota Beet Sugar Cooperative’s new Application 0 program that was discussed in the July 3 issue of Minnesota Farm Guide. The July 3 article suggested that a strobilurin or an EBDC (Mancozeb) product could be used for Application 0, when in fact only an EBDC fungicide can be used in the SMBSC region. This reporter apologizes for any misunderstanding.