July 17, 2003

 

Cercospora Leaf Spot Appears in Area Fields

Sugarbeet Cercospora leaf spot infection has been confirmed in the Moorhead and Crookston factory districts, according to Mohamed Khan, North Dakota State University and University of Minnesota Extension Sugarbeet Specialist. Cercospora spores were also collected at Foxhome in the Wahpeton factory district.

"Cercospora leaf spot is the major disease of sugarbeet in our region, reaching epidemic levels in 1997 and 1998," Khan says. "In 1998, growers lost $75 million to the disease. To compound the problem, the pathogen has developed resistance to the Benzimidazole class of fungicides and tolerance to tin, another fungicide."

Cercospora infection produces circular spots about one-eighth inch in diameter with ash gray centers and dark brown or reddish-purple borders. In humid conditions, the spots may become gray and velvety with the production of spores. The spores further the spread of the disease especially within fields, resulting in many infection cycles during the growing season.

The most common source of the cercospora fungus is infected sugarbeet debris in the field. The fungus is spread mainly by wind and water and develops rapidly in warm, humid and rainy weather. Day temperatures of 80 to 90 degrees F and night temperatures above 60 degrees F with humidity above 87 percent favor disease development. Symptoms of the disease may appear five to seven days after infection.

"Many growers whose fields have closed rows have started fungicide applications," Khan says. "We have a number of effective fungicides for cercospora control. Growers should consult with their agriculturist to determine the fungicide that will be the most effective for control in their district."

For growers trying to control Cercospora and grass weeds, the safest combination will be Eminent plus an adjuvant and an effective grass herbicide such as Select or Poast. Headline can also be mixed with grass herbicides, but the adjuvant rate should not exceed 0.5 percent v/v of water. "Growers should remember to alternate fungicides from different classes and never use the same product back-to-back," Khan says.

This year sugarbeet growers in North Dakota and Minnesota have planted more than 728,000 acres to beets which is the largest acreage ever planted to the crop in this region.

###

Source: Mohamed Khan, (701) 231-8596, mkhan@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu