Evaluation of Fungicides to Protect Asparagus Fern from <i>Stemphylium vesicarium</i> and Provide Extended Control

Purple spot, a fungal disease caused by Stemphylium vesicarium, renders spears unmarketable and on the fern, causes premature defoliation which can decrease next year’s yield and quality. Fungicides, including azoxystrobin, mancozeb, and chlorothalonil, are applied to the foliage according to the TOMCAST disease forecaster at 15 disease severity values (DSVs) in order to manage purple spot disease. The objective of our study was to identify fungicides that control purple spot disease on asparagus fern. The ability of fungicides to provide extended protection was of interest. Twelve fungicides, alternated with chlorothalonil, were applied to ‘Sequoia’ asparagus fern every 9-11 days and compared to an untreated control in 2022 and 2023. Relative area under the disease progress curve (rAUDPC) data indicated that all treatments within and beyond the interval period limited purple spot disease compared to the control except for fluopyram + pyrimethanil (2022), and pyrimethanil (2022). For industry standards, azoxystrobin had a lower disease severity than the control both within and beyond the treatment interval. Pydiflumetofen + fludioxonil, and fluxapyroxad + pyraclostrobin consistently had the lowest rAUDPC among unregistered fungicides within and beyond the treatment interval. The registration of new fungicides can protect the fern from purple spot and expand management options for growers.