More rain than needed, so scout for disease

Tony Nye - OSU Extension

You’ve all heard the old saying, “Rain, rain go away!” I am not sure there are many folks that don’t feel that way. The continued rain events have made it difficult for many forage producers to get hay harvested around Ohio.

Now we are starting to harvest wheat, and if the rain does not stop soon, that can be detrimental to the quality of grain harvested as well as straw.

The current weather is also a perfect storm for disease development in our growing crops.

Many farmers and consultants have begun scouting and checking their soybean stands for possible disease presence.

According to Anne Dorrance, plant pathologist at Ohio State University, they are finding lots spots on the leaves. Some could be potential issues.

Dorrance notes 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. Dorrance and others have done extensive studies on this disease over the past decade and have yet to attribute an economic value in managing this.

Researchers did one experiment where they 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.

Another disease being found is Septoria brown spot. Dorrance says that at todays’ fungicide application costs and soybean prices, this is a hard one to even break even on.

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.

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.

Don’t forget to scout corn as well. We may have found our first signs of Northern Corn Leaf Blight.

A word of wisdom is to do your homework on the appropriate fungicides to use. Consider timing, costs and economic thresh hold of disease.

If you can’t get out in the fields and you like technology try to watch new episodes of the Agronomy and Farm Management Podcast.

According to Extension professionals, Elizabeth Hawkins and Amanda Douridas, two new episodes of the Agronomy and Farm Management podcast are available this month.

In Episode 3, released June 13th, Dr. Mark Loux provides advice for managing some of Ohio’s toughest weeds! Episode 4, coming June 27th will help prepare you for disease scouting with Drs. Pierce Paul and Anne Dorrance sharing tips for identifying and managing common diseases of corn, wheat, and soybeans.

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Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for 29 years, currently serving Clinton County and the Miami Valley EERA.

Tony Nye

OSU Extension