An in-field heat treatment to reduce Cercospora beticola survival in plant residue and improve Cercospora leaf spot management in sugarbeet

Authors: HERNANDEZ, ALEXANDRA - Michigan State University; BUBLITZ, DANIEL - Michigan State University; WENZEL, THOMAS - Michigan State University; RUTH, SARAH - Michigan State University; BLOOMINGDALE, CHRIS - Michigan State University; METTLER, DAVID - Southern Minnesota Beet Sugar Cooperative; BLOOMQUIST, MARK - Southern Minnesota Beet Sugar Cooperative; Hanson, Linda; WILBUR, JAIME - Michigan State University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2023
Publication Date: 5/9/2023
Citation: Hernandez, A.P., Bublitz, D.M., Wenzel, T.J., Ruth, S., Bloomingdale, C., Mettler, D., Bloomquist, M., Hanson, L.E., Wilbur, J.F. 2023. An in-field heat treatment to reduce Cercospora beticola survival in plant residue and improve Cercospora leaf spot management in sugarbeet. Frontiers in Plant Science. 14. Article 1100595. https://doi.org/10.3389/fpls.2023.1100595.
DOI: https://doi.org/10.3389/fpls.2023.1100595

Interpretive Summary: Sugar beets account for a little over half of domestic sugar production. This production is impacted by several diseases. Among these, Cercospora leaf spot is the most important foliar disease. A major method of survival for this pathogen is in infected leaf debris. Plowing has been an important management tool for reducing the impact of this disease, but current recommendations for reduced tillage to limit soil erosion mean alternative methods of management are needed. This study compared a heat treatment, either just before harvest in the autumn, or shortly before planting in the spring, and a chemical desiccant treatment, compared tothe standard of tilling in leaves. While the chemical desiccant did not have a significant impact on fungal survival or disease severity, both the autumn (P<0.05, 2019/2020 and 2020/2021) and spring (2019, P < 0.05; 2021, P < 0.0001) heat treatments significantly reduced disease severity in the field for the following beet crop. Thus, heat treatment of fresh or overwintered leaf tissue could be an aid in Cercospora leaf spot management and an alternative to plowing. This method could be used in conventional and organic production.

Technical Abstract: Sugarbeets account for 55 to 60% 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 C. beticola primarily survives in infected leaf tissue between growing seasons, this study evaluated management strategies to reduce this type of inoculum overwintering and survival. Treatments included the historic standard, moldboard plowing immediately post-harvest (6-in. depth), with heat treatment with a propane-fueled burner either immediately pre-harvest or just prior to planting, or application of a desiccant (saflufenacil) 7 days pre-harvest. After harvest treatments, leaf samples were evaluated at 0-, 45-, 90-, and 135-days post-harvest to determine C. beticola sporulation and 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. For spring-applied treatments, disease assessments were done by rating disease severity through the season. The at-harvest heat treatment significantly reduced lesion sporulation (2019-20 and 2020-21 trials, 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 at-harvest treatments were applied (2019 and 2020; P < 0.05). In 2019 and 2021, the propane-fueled heat treatment of leaf residue in the spring resulted in similar reductions in CLS severity in Minnesota field studies (2019, P < 0.05; 2021, P < 0.0001). Based on these results, heat treatment of fresh or overwintered leaf tissue could be used to aid in CLS management.