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Examples of Northern Corn Leaf Blight

Disease pressures in some Ohio corn fields hitting economic thresholds

There is no doubt that Ohio’s growing season has about as many variations as possible when it comes to the dates the crops were planted, to the uneven stands and to the current stages of the crop.

One thing that has caught the eye of one agronomist is the level of diseases, such as Gray Leaf Spot (GLS) and Northern Corn Leaf Blight (NCLB), in certain areas of the state.

“I’m not sounding any alarms to call in airplanes just yet but I want everybody to know several fields down by Mechanicsburg, Marysville, and South Charleston have reached economic thresholds for those diseases,” said Stewart Seeds agronomist Justin Petrosino. “Most of the fields I’ve walked into I have found a little bit down on the bottom leaf which is nothing to worry about, but a few fields have significantly more pressure that does cause some concern.”

Examples of Grey Leaf Spot
Examples of Grey Leaf Spot

If you are seeing 5% leaf coverage on 50 % of the 3 leaves below the ear leaf with humid conditions and more rainfall in the forecast you reached the economic threshold. An application at this point of the growing season is a very tough decision with corn hitting $3.80.

“When you look at the cost of flying on a fungicide at tassel, you need at least 10 bushels of corn gained back from loss just to pay for that application,” Petrosino said. “This is an important time to be out scouting to see if your fields are also at that economic threshold and call your seed rep to double check that the hybrid is susceptible.”

Single mode of action products will likely be cheaper but dual mode of action products can help with fungicide resistance management and also provide better control. Hit your corn fields and scout, scout, scout because with an application at this stage of the season, timing is everything.

“The idea application window is between two weeks before tassel up to tassel as long as the plane can come in at a timely manner,” said Petrosino. “Once you start to see brown silks you are losing a little more on your payback.”

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