Less Efficacy: UGA Onion Trials Show Reduced Impact on Botrytis Leaf Blight

Clint Thompson Disease, Georgia, Onion, Top Posts

Photo by Chris Tyson/UGA: Here is a large botrytis leaf blight lesion that has sporulated and the “cloudy halo” appears around the initial spot on the leaf. The development of these symptoms increases during periods when leaves stay wet for several hours at a time.

University of Georgia research trials show that two fungicides may be losing their efficacy in the control of Botrytis Leaf Blight of Vidalia onions.

Chris Tyson, University of Georgia Extension Area Onion Agent at the Vidalia Onion & Vegetable Research Center in Lyons, Georgia, informed onion producers and industry leaders during a webinar last week that Scala and Luna Tranquility have shown reduced efficacy in controlling Botrytis, a disease onion producers contend with every year.

“Most of this information has not changed but (Bhabesh Dutta) did stress and wanted me to mention to you about Scala and Luna. Within the last year or so, he says they have started to slip a little bit in how well they worked for Botrytis,” Tyson said. “Don’t misunderstand us. He’s not saying not to use these products. But we just want to make you aware we may take them off this list. We may rearrange them in the future to reflect that. They’re still good products. We still want you to use them.”

Disease Symptoms

Botrytis Leaf Blight infects onion foliage. Initial symptoms include white, necrotic spots surrounded by pale halos. Leaves with severe symptoms may lead to reduced bulb size.

The most updated list of effective fungicides includes Omega 500 and Miravis Prime, both of which provide high-to-moderate control. Scala provides high-to-moderate control as well, and Luna provides moderate control. But if the trend continues, UGA may adjust their recommendations to reflect the diminished efficacy of those two options.

“Keep in mind the only change in Botrytis control from last year is that those (two treatments) haven’t looked quite as good. They’re still providing control, just not at the level we thought they might be,” Tyson said.

Omega 500 is a valuable option since it controls Downy Mildew as well.