Appearance of Frogeye Leaf Spot in Arkansas - August 2012
[University of Arkansas Division of Agriculture Research and Extension University of Arkansas System. Arkansas Soybean Promotion Board. Travis Faske, Ph.D., Extension Plant Pathologist, University of Arkansas Division of Agriculture, Lonoke Research and Extension Center]
[Video shows Faske standing in a soybean field.] Hello, my name is Travis Faske. I’m an extension plant pathologist for the University of Arkansas and today I want to talk to you about frogeye leaf spot.
[Picture of a soybean plant showing frogeye leaf spot on soybean plants.] Frogeye leaf spot is a common disease found in Arkansas. It’s caused by the pathogen Cercosproa sojina and it is easily recognizable by its foliar symptoms which is a tan center circled by a purplish or brownish margin. Strobilurin-resistant frogeye leaf spot was found in Arkansas. This resistance means that this pathogen is resistant to all strobilurins, not just one.
[Slide showing Petri dishes.] This is an in vitro laboratory assay of how the strobilurin resistant isolates frogeye leaf spot respond to azoxystrobin. Here we have the susceptible isolate on the top. Here are the resistant isolates. As you can see, as we move to the left, we increase in the amount of fungicide that is on each dish. Here, this isolate responds very quickly, there’s no growth here, where here we have growth at the very low rate. We also have growth at the very high rate.
To get the same response that we observe here in these two isolates would require 280 times more of the azoxystrobin fungicide in the field.
[Video shows Faske standing in a soybean field.] There are several management tactics to reduce the selection of fungicide-resistant frogeye leaf spot. First, utilize resistance in high risk areas. Resistance is the most economical method to manage disease. Second, choose a fungicide chemistry class that is different than the strobilurins, or that has another combination of the fungicide with the strobilurin, like a triazole or the thiophanate methyl group. Finally apply fungicides when the symptoms are observed in the field rather than just applying when there are no symptoms observed. [Video shows soybean plants in a field.]
To find out more update information about stroberian resistant frogeye leaf spot, contact your local county extension agent, or online at www.uaex.edu
[www.uaex.edu. University of Arkansas Division of Agriculture Research and Extension University of Arkansas System. Arkansas Soybean Promotion Board]