Cercospora Leaf Spot Impact on Sugarbeet

One of the challenges for the 2016 Sugarbeet season was Cercospora Leaf Spot. Cercospora causes crop losses by decreasing the crop’s yield and sugar percent. Additional losses may occur in the storage season due to increased impurities and respiration losses. These losses make planning for control of Cercospora to be on the forefront of grower’s minds so they can seek methods to limit the effects of this disease.

Lesions of Cercospora initially occur on older leaves and then progress to new leaves. Lesions on leaves are approximately 1/8 inch in diameter. Proper identification is required as Alternaria leaf spot, Phoma leaf spot, Ramularia leaf spot, and Bacteria leaf spot can all be confused with Cercospora. A diagnostic feature of Cercospora is the presence of tiny black dots that form near the center of the older lesions. If control measures are not implemented, lesions will eventually take over the whole leaf. Fields will appear brown instead of green in severe situations.

Optimum conditions for Cercospora are temperatures between 77-95 F and night time temperatures above 60F and high humidity between 90-95%.  Also, leaf wetness over 12 hours increases chances of Cercospora incidence. These conditions are not within a grower’s ability to control, but knowing what contributes to the promotion of Cercospora can help growers know when to treat with a fungicide.

Photo Courtesy of Mohamed Khan NDSU

Management Practice to Control Cercospora

Management practices can be used to assist in the control of Cercospora. Three-year rotations with non-host crops should be used to decrease inoculum carryover. Tilling after a sugarbeet crop that was infected with Cercospora should bury leaf tissue to reduce inoculum. Also having separation from previous fields inoculated with Cercospora will help with control.  Planting resistant varieties are one of the best things that can be used to control Cercospora. It is best for growers to consult with Crop Consultants and seed company personnel to purchase varieties with high resistance.  Finally, use proper fungicide programs to reduce the effects of Cercospora.

Now is an excellent time to think about the upcoming year. Growers have time to purchase varieties that will perform well under Cercospora pressure. Growers may also receive training about proper fungicides to use, so they are prepared to start applying when the conditions are right. Cercospora is challenging for growers but with proper management, it can be controlled and to allow for a great crop.