By Anne Dorrance, Ohio State University Extension plant pathologist
From the scouting reports from the county educators and crop consultants, most of the soybeans in the state are very healthy with no disease symptoms.
However, as the news reports have indicated, there are a few varieties in a few locations that have higher incidence of frogeye leaf spot than we are accustomed to seeing at this growth stage — mid R2 through flowering in Ohio. Most of the reports to date are along and south of route 70, which based on the past 12 years is where frogeye is the most common. When this disease occurs this early in the season, where it can be readily observed, this is a big problem and should be addressed right away with a fungicide soon and a second application at 14 to 21 days later depending on if disease continues to develop and if environmental conditions (cool nights, fogs, heavy dews, rains) continue.
What if there is no frogeye on the varieties in your area? Wait and keep scouting. If you know your seed company’s resistance rating scale and your variety has good resistance, then you just saved a lot of money by not having to spray a fungicide.
We know from previous work that if frogeye does not appear in a field until growth stage R5 — on a susceptible variety — there is no yield loss. This is most common in the northern part of Ohio (route 30 and north), it’s rare to have a fungicide pay for frogeye leaf spot. This disease does not really begin to move until later in the season.
This disease is fairly easy to scout for. The newer leaves are the ones that are susceptible not the older, fully expanded leaves. So take a look before you buy. Check your variety ratings and keep listening to where it has been detected in your area. More importantly, we do need to evaluate if any of the strains of C. sojina are susceptible to frogeye leaf spot in the state, so please send us leaves with lesions.