By Clint Thompson
If history is any indication, downy mildew can happen any time in Georgia’s Vidalia onion crop. Growers can ill-afford to get behind the eight-ball with regards to managing this “destructive” disease, says University of Georgia Extension Vegetable Plant Pathologist Bhabesh Dutta.
“There’s a reason people named it a destructer, because it destroys pretty much everything in three weeks. In three weeks, if you don’t spray anything, you won’t have any crop,” Dutta said. “It’s that bad.”
The disease’s occurrence in recent years has been reported around the early-to-mid March timeframe. It was first discovered March 6 in 2024 and March 2 in 2023. It was not reported in 2021-22 but was confirmed on March 23 in 2020.
The first symptoms of downy mildew occur on older leaves as light green to pale yellow, which turn to tan and brown as the lesion ages. In Georgia, early symptoms can be diamond-shaped lesions that are mottled with pale and green areas interspersed. As colonization progresses, lesions may girdle the entire leaf. This could cause the total collapse of leaf tissues.
Infected bulbs are reduced in size and typically don’t store well. In severe cases, 100% yield losses have been reported.