It’s Probably not Frogeye Leafspot and no Brown Spot IS NOT an Economically Important Disease

Jun 19, 2018

By Anne Dorrance

As farmers and consultants have been out checking their soybean stands, they are finding spots on the leaves. The most common spotting on the unifoliates and first leaves is caused by Septoria glycines. This is a fungus that overwinters on the previous soybean crop residue and in modern cultivars it is limited to the lower canopy. We’ve done extensive studies on this disease over the past decade and I have yet to attribute an economic value in managing this. We did this one experiment where put chlorothalonil on every week (not a legal application but for research purposes only) and could only measure a 3 to 4 bu increase when the soybean plants were totally clean of this disease. Secondly, applications of herbicide plus fungicide did not manage this disease throughout the season nor do the R3 applications. At todays’ fungicide application costs and soybean prices, this is a hard one to even break even on.

Septoria brown spot

The one disease we have gotten substantial response to fungicide applications, is with frogeye leaf spot. There are a few high yielding soybean cultivars that are very susceptible to this disease. Yield losses of 8 to 35 bushels have been recorded. The fungus that causes this disease can overwinter in Ohio, this was confirmed by studies in Illinois as well. This fungus, Cercospora sojina, can also spread via large storm fronts, hurricanes from southern states where it can build up and the spores can be carried to new areas. This happened in 2005 and again last summer based on my own scouting of test plots. The symptoms are gray centers surrounded by a deep purple circle which forms the lesion. Under high moisture conditions,the spores of the fungus will form in the lesion on the underside of the leaves, actually look like whiskers. There are a few herbicides, adjuvants, foam markers that under the right conditions will cause similar looking symptoms. The easiest way to check is to place leaves with these symptoms in a plastic bag and see if they form the whiskers – or spores overnight. These bags just need humidity – not a lot of free water. Also note, this fungus will infect new leaves and if it is established with every rain event there will be continual infections of the new foliage.

Frogeye

To manage this disease, foliar applications at R3 have been very good in Ohio at managing this pathogen. One note is that we have documented that strobilurin resistance is here in Ohio, so if you have any questions please send us these leaves, we do have time to test the fungicide sensitivity before you will need to spray.

Source: osu.edu

Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.