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Combat cercospora leaf spot

Allexxandar/Getty Images Sugar beets
FOLIAR FUNGUS: The most common source of the fungus, Cercospora beticola, is infected sugarbeet debris in the field. The fungus spreads from field to field mainly by wind.
Cercospora leaf spot is the No. 1 foliar disease affecting sugarbeets in Minnesota and North Dakota.

Cercospora leaf spot is the most damaging foliar disease affecting sugarbeets, and is caused by the fungus Cercospora beticola. This disease results in lower tonnage, lower sucrose concentration, reduced extractable sucrose and increased impurities that lead to higher processing costs.

The most common source of the fungus is infected sugarbeet debris in the field. The fungus spreads from field to field mainly by wind. Cercospora leaf spot develops rapidly in warm and wet conditions. Day temperatures of 80 to 90 degrees F and night temperatures above 60 degrees favor disease development. Leaf spot symptoms may occur five to seven days after infection under favorable conditions.

Cercospora infection produces circular spots about an eighth-inch in diameter, with ash gray centers and dark brown or reddish-purple borders. Severe infections will result in leaves dying.

Combating cercospora

For sugarbeets with a severe cercospora infection, the spots may become gray and velvety with the production of spores. These spores further spread the disease, especially within fields, resulting in many infection cycles during the growing season.

Because of the multicyclic nature of the pathogen, control cercospora leaf spot early by using an integrated approach, including these practices:

  • burying infected tops by tillage
  • planting improved tolerant varieties especially CR+ varieties
  • using a crop rotation interval of at least three years
  • selecting fields as far away as possible from the previous year’s infected field
  • applying timely, recommended fungicide mixtures in high water volume (15 to 20 gallons per acre)

Infected leaf samples are collected annually from all factory districts in Minnesota and North Dakota. These samples are tested to determine sensitivity of the fungus to the different fungicides used in their control.

C. beticola has developed resistance or reduced sensitivity to most of the fungicides used for its control. Currently, no individual fungicide provides season-long control of the fungus. Mixtures that contain a multisite fungicide and used in a rotation program are most effective at controlling C. beticola. Consult your agriculturists for fungicide mixtures recommended for your factory district.

Research done at North Dakota State University and the University of Minnesota showed that application of effective fungicide mixtures after rows are closed and at disease onset, or at first symptoms in a field or factory district, with subsequent applications based on the presence of leaf spots and favorable environmental conditions, consistently provided the most effective and economical control.

Frequent rainfall, especially soon after fungicide application, reduces the efficacy of fungicides. Sugarbeet fields with more susceptible varieties with closed rows that are close to shelterbelts, waterways or previously infected fields should be the first to be scouted since they would be the first to become infected.

The most effective strategy to manage the fungus is to use improved tolerant varieties (where available) with judicious timely fungicide applications. The development and availability of CR+ varieties with improved resistance to C. beticola will contribute significantly to managing leaf spot.

Source: North Dakota State University, is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.
TAGS: Fungicide
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