An in-field heat treatment to reduce Cercospora beticola survival in plant residue and improve Cercospora leaf spot management in sugarbeet.
Sugarbeets account for over 50% of U.S. sugar production. Cercospora leaf spot (CLS), primarily caused by the fungal pathogen Cercospora beticola, is a major foliar disease of sugarbeet. Since this pathogen survives in infected leaf tissue, this study evaluated management strategies to reduce inoculum overwintering and survival. Treatments included moldboard plowing immediately post-harvest (6-in. depth), heat treatment with a propane-fueled burner at 1 mph immediately pre-harvest, and application of a desiccant (saflufenacil) 7 days pre-harvest. After treatment, leaf samples were evaluated at 0-, 45-, 90-, and 135-days post-harvest to determine C. beticola viability. The following season, inoculum pressure was measured by taking disease ratings on a susceptible beet variety planted into the same plots, and by counting lesions on highly susceptible sentinel beets placed into the field at weekly intervals. The heat treatment significantly reduced lesion sporulation (2019-20 and 2020-21 trial; P < 0.0001, 2021-22 trial; P < 0.05) and C. beticola isolation (2019-20 trial; P < 0.05) in at-harvest samples. Reduced numbers of CLS lesions were observed on weekly sentinel beets placed in heat-treated plots from May 26-June 2 (P < 0.05) and June 2-9 (P < 0.01) in 2019, as well as June 15-22 (P < 0.01) in 2020. The heat treatment also reduced the area under the disease progress curve for CLS assessed the season after treatments were applied (2019 and 2020; P < 0.05). In 2019 and 2021, a propane-fueled heat treatment of leaf residue in the spring resulted in similar reductions in CLS severity in Minnesota field studies. Overall, heat treatment of fresh or overwintered leaf tissue could be used to aid in CLS management.