Cercospora Leaf Spot: If you see it, you're too late

*photo courtesy of cropwatch.unl.edu

Cercospora leaf spot is the most virulent and destructive foliar disease of sugar beet on the western plains. The fungal pathogen Cercospora beticola is endemic throughout sugar beet growing areas and easily overwinters on improperly destroyed residue, creating consistent issues for even well-managed fields. It became a significant pest in the mid-1920s, causing a shift in sugar beet production to western states that continues to this day.

Cercospora leaf spot can cause yield losses of more than 40% and affect storability of the beets after harvest, continuing to cause financial losses even after the growing season. Symptoms begin as small necrotic lesions on lower leaves, rapidly progressing to younger tissue if left untreated. As the disease progresses the lesions can coalesce into large areas of necrotic tissue and infected leaves will begin to yellow outside of the lesions. Cercospora leaf spot can be easily misidentified as Alternaria, though is distinguished by the presence of black spores in the center of the lesions, best seen when viewed through a hand-lens.

The conditions most favorable for Cercospora leaf spot development are when daily low temps exceed 60 degrees and humidity exceeds 90%. Cool nights and dry winds can help delay the onset of disease, but growers should be mindful of waiting until disease lesions are visible before treating with a fungicide. The UNL Panhandle Research and Extension Center offers a disease modeling and prediction tool based on daily temps and humidity. Basing fungicide applications on predictive risk instead of visual confirmation allows timelier applications to lower levels of disease inoculum; to wit, if you see it, you’re too late.

Priaxor, Provysol, and Veltyma Fungicides all have a fit in Cercospora leaf spot management. Follow your local BASF recommendations for best timing and management practices. Always read and follow the label.