Cercospora Leaf Spot on Sugarbeet

The fungus Cercospora beticola causes the Cercospora leaf spot, which is the most serious foliar disease of sugarbeet in Minnesota and North Dakota. This disease results in low tonnage, low sucrose concentration, reduced extractable sucrose and increased waste leading to higher processing costs. The most common source of Cercospora fungus is infected sugarbeet litter in the field. The fungus spreads from field to field mainly by wind. Cercospora leaf spot develops rapidly in warm and humid conditions. Daytime temperatures of 80-90° F and nighttime temperatures above 60° F favour disease development. Leaf spot symptoms may appear 5-7 days after infection under favourable conditions. Cercospora infection produces round spots about 1/8 inch in diameter with ash-grey centres and brown or reddish-purple borders. Severe infection causes leaf death.

In humid conditions, the spots may become grey and velvety due to the production of spores. These organisms continue to spread the disease, especially in fields, causing multiple cycles of infection during the growing season.

Due to the multi-pathogenic nature, it is important to have the first control of the Cercospora leaf spot in an integrated way. This includes cultural practices such as covering infected tops by planting, planting improved resistant varieties, especially CR+ varieties, using a rotation period of at least three years, selecting distant fields as much as possible from the field of the previous year, and the correct and correct time. The correct use of fungicide compounds is recommended in water (15 to 20 GPA).

Samples of infected leaves are collected annually from all factory counties in Minnesota and North Dakota. These samples are tested to determine if the fungus is sensitive to the different fungicides used in their control. C. beticola has developed resistance and reduced sensitivity to many fungicides used for its control. Currently, no individual fungicide provides long-term control of CLS. Compounds containing multiple fungicides used in a rotation program are most effective in controlling CLS. Consult your agronomist for fungicide combinations recommended for your plant region.

Research conducted at NDSU and the University of Minnesota has shown that the use of active fungicide compounds after the rows are closed and when the disease begins, or the first symptoms in the field or the factory district, with the following applications based presence of leaf spots and good environment. conditions, provides the most efficient and economical CLS control (https://apsjournals.apsnet.org/doi/epdf/10.1094/PDIS-91-9-1105). Frequent rain, especially immediately after fungicide application, reduces the effectiveness of fungicides. Information on disease susceptibility in your area based on weather conditions is available. 

Sugarbeet fields with susceptible varieties with closed rows near buffer zones, waterways, and previously infested fields should be the first to be screened as they will be the first to be infected. The most effective strategy for controlling CLS is to use improved resistant varieties (where available) with timely fungicide applications. The development and availability of CR+ varieties with improved resistance to C. beticola will contribute significantly to controlling leaf spots.