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LSU AgCenter plant pathologist Sara Thomas-Sharma is studying two diseases that affect soybeans: Cercospora leaf blight and aerial blight.
Cercospora has been a leading foliar disease in soybeans for many years in the U.S. South. Usually appearing while plants are in the reproductive stages of development, the disease can affect seed production and cause yield and quality losses.
Thomas-Sharma is in the third year of a project examining how the timing of fungicide applications and cultivar resistance affect incidence of Cercospora. She has planted trials in Baton Rouge, Winnsboro and Alexandria with one Cercospora-resistant variety and one variety that is susceptible to the disease. The trials will be sprayed with the Revytek fungicide.
“The focus will be on whether the applications timed close to spore peaks will be more efficacious,” Thomas-Sharma said.
Her earlier work on the project has shown that spores of the pathogen that cause Cercospora tend to peak several times before symptoms are observed on plants. She uses spore traps in field trials to monitor their presence.
Members of LSU AgCenter plant pathologist Sara Thomas-Sharma's lab work in a soybean field where disease management strategies are being studied. Photo provided by Sara Thomas-Sharma.
“Fungicide applications to target spore peaks show promising yield and economic trends,” she said. “However, the results are not consistently statistically significant, suggesting that optimization in fungicide application timing is much needed.
She’s also studying spore data collected since 2019 to see whether weather variables had any effect on spore peaks. If any trends are identified, that information could help predict spore peaks and determine when to make targeted fungicide applications.
On the issue of aerial blight, Thomas-Sharma recently launched a new project that involves screening new soybean varieties for resistance to the disease. Aerial blight causes small lesions on plants early in the growing season. As the disease progresses, severe damage can occur, with infected leaves, stems and pods often sticking together.
Thomas-Sharma is working on this project in a greenhouse rather than in a field.
“A greenhouse assay is necessary for this pathogen because, as a soilborne pathogen, it is patchy in the field,” she said. “Thus, varieties may escape disease rather than truly being resistant if screened only in the field.”
The varieties she is testing for aerial blight resistance are in the AgCenter’s core block trials this year. They will be available for planting in 2025, and results from her resistance screenings will be provided to help farmers choose varieties.
