Curbing Frogeye
Specialist Offers Tips For Fighting Strobilurin Resistance
MILAN, TENN.
Foliar fungicides and seed treatments are the recommendations of Dr. Melvin Newman for the treatment of strobilurin resistant frogeye in soybeans. Newman, extension plant pathologist for the University of Tennessee located at Jackson, Tenn., made those comments at a field day recently.
“I’ve been working in soybeans, corn, cotton and wheat for many years now, working mainly with foliar fungicides and resistant varieties,” he said. “Frogeye resistance to the strobilurin fungicides has developed in about 15 locations already around the mid south; even into Louisiana there have been cases of frogeye leaf spot in soybeans that is resistant to the strobilurin fungicides such as Quadris, Headline and others in that class of fungicides. As producers have sprayed the strobilurins out year after year, the fungus has developed resistance to it.”
Some fungicides, mainly in the class of triazoles or mixtures of a triazole with a strobilurin, will help control the frogeye leaf spot disease. There also are a number of varieties that have been tested here at the Milan Experiment Station that are totally resistant to both the normal frogeye leaf spot and also the strobilurin resistant “strain.”
“So farmers ought to pay attention to our ratings that we have on the website at utcrops. com,” he added. “You can find many years of data on resistant varieties and fungicide results. Year after year varieties come and go, so we test every year and rate the varieties under heavy disease pressure with and without a foliar fungicide. So take a look at that website and you will learn a lot about commercial varieties and to which diseases they are resistant or susceptible to.”
Another practice farmers can use for disease control in general on just about any crop is to rotate the crops.
“I understand the price you get for your commodities is very important,” Newman said. “The soybean prices are so good now that it’s hard not to plant soybeans and/or corn. I know that plays a big part, but the more you rotate your crops the less disease you’re going to have in just about every case.”
As he spoke, Newman stood in a field of beans that was in corn last year. There was very, very few diseases visible in that crop.
“The question comes up, should I spray a fungicide on these beans? Well, there’s going to be some disease come in eventually and it doesn’t take but a bushel or two to pay for the fungicide application now with the really high price of beans. Many folks are spraying their soybeans for extra yield.
“Yet some say, ‘well if I spray a fungicide I’m going to have more resistance buildup.’ My answer is if you don’t have any disease then you’re not going to have much chance for resistant buildup anyway. It would be pretty uncommon not to be able to expect an extra bushel or two from spraying a fungicide.”
On the other side of the coin, if the beans are very, very poor and drought stricken and the roots are rotten with charcoal rot, which is common in a drought, then maybe there’s no need to spray.
“However, if you have good beans with susceptibility to frogeye or other foliar disease and the price is very good, it’s probably okay to go ahead and spray,” he reasoned. “So that’s our recommendation: Use disease resistant varieties, spray fungicides as needed, and rotate crops as much as possible.
“One really good idea is to treat your soybean planting seed with a recommended fungicide seed treatment,” he added. “That will help a little bit even on the foliar disease side of the spectrum. It cleans up the seed from disease spores, gives you better vigor and a better chance of good emergence. So treating the seed and foliar fungicides are good practices to consider these days as commodity prices are really good. Δ
BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
Dr. Melvin Newman, extension plant pathologist for the University of Tennessee, recommends foliar fungicides and seed treatments for strobilurin resistant frogeye.