WEST FARGO, N.D. — Cercospora leaf spot remains a formidable sugarbeet disease and one that farmers must control, university Extension experts told farmers at the Sugarbeet Research and Reporting Session.
The disease, which affects sugarbeet plants during the growing season, is spread by wind, water and insects.
“It still is the most important problem faced by growers in North Dakota and Minnesota,” said Mohamed Khan, North Dakota and University of Minnesota sugarbeet specialist.
The sugarbeet disease, which has potential to trim yields as much as 40% and reduces quality, results in major monetary losses and also decreases the storability of the crop, said Peter Hakk, NDSU and U of M sugarbeet specialist.
For example in 2016, cercospora leaf spot resulted in more than $140 million in sugarbeet losses in North Dakota and Minnesota, Hakk said.
Khan and Hakk were among several speakers who presented research at the 52nd annual sugarbeet reporting session. The session held Jan. 11, 2022, in West Fargo, was sponsored by NDSU and U of M Extension and the Sugarbeet Research and Education boards of Minnesota and North Dakota.
The research reporting sessions provided information about studies on sugarbeet disease, insect and fertilizer topics that affect growers who produce crops for American Crystal Sugar Co., based in Moorhead, Minnesota, Minn-Dak Famers Cooperative in Wahpeton, North Dakota, and Southern Minnesota Beet Sugar Cooperative in Renville, Minnesota.
Cercospora leaf spot, which thrives during warm, humid and rainy weather, is characterized by circular spots that are about one-eighth to three-sixteenth of an inch in diameter. The spots' centers range in color from light to dark tan and the borders from dark brown to reddish purple, according to NDSU Extension. The leaf blades, veins and petioles of plants that have cercospora leaf spot also may have elliptical lesions.
Leaf spots typically develop from five to 21 days after infection, depending on the amount of inoculum, temperature and duration of wet period.
Cercospora control requires a holistic approach which includes crop rotation, planting tolerant sugarbeet varieties and spraying a mixture of fungicides, Khan said.
Triphenyltin hydroxide or another triazole should be used with other mode of actions such as ethylene bisdithiocarbamate, or two multi-site fungicides in each application, Khan said.
Research shows that the mixtures of fungicide effectively control cercospora leaf spot and result in an acceptable level of recoverable sugar when rain didn't wash them off, Khan told farmers.
DeMethylation Inhibitors, commonly called DMIs, performed best when tank-mixed with certain “partners,” Hakk said. Besides mancozeb and copper, potential partners include phosphite, sulfur and biologicals.
Development of resistance to DMI from tank mixing with partners is being evaluated, Hakk said.
Using proven disease tolerant varieties, meanwhile, reduces fungicide use and provides high recoverable sucrose if fungicide application becomes an issue, Khan said.