From Clemson Plant Pathologist Tony Keinath.
Cercospora leaf spot is the most damaging disease on beet greens and bunched beets. This disease is one of the few diseases I have worked with that can be managed equally well by conventional and organic fungicides. Based on previous research in New York with processing beets, I tested the best conventional program, Tilt alternated with Quadris, and the best organic program, Cueva + Double Nickel, on six beet cultivars grown and harvested for greens in spring 2021.
The results with fungicides were clear cut but not that encouraging overall. The good news is that both programs reduced the severity of Cercospora leaf spot compared to the water-sprayed control. The not-so-good news is that spraying did not increase the number, weight, or percentage of healthy leaves (data not shown). Fungicides worked the same across the six beet cultivars tested (see this previous post for the list of cultivars and their reactions to Cercospora leaf spot).
Note that Quadris on beets must be rotated 1:1 with another fungicide. Tilt was chosen for this trial instead of the less expensive Monsoon (generic tebuconazole), because lab fungicide sensitivity testing of SC Cercospora isolates showed they are more likely to be sensitive to Tilt than Monsoon. The question remains whether spraying beets for Cercospora leaf spot is worth the cost. From a strictly economic perspective, the answer, at this point, is not really. The trial is being repeated in spring 2022 to verify the results from 2021.