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Does Your Corn Have Gray Leaf Spot?

Severity varies with planting date, hybrid.

Tom Bechman 1, Editor, Indiana Prairie Farm

July 19, 2010

2 Min Read

Over half of the 22 samples of corn, three stalks each, brought to the Franklin County 4-H fair for judging last week had at least a few gray leaf spot lesions on leaves. In some cases there were only a few. In a couple cases, there were several, and they were moving up the plant toward the ear lead. It was the teachable moment for me, as the judge, and the 4-H'er, as we discussed their project and their specimens in one-on-one conversations.

The more people who know what gray leaf spot looks like, especially in the younger generation who help mom and dad on the farm, the better job of scouting we can expect in the future. Or at least that's the theory I'm banking on.

The reason many of the exhibits had at least a few lesions, albeit normally small lesions, was that gray leaf spot threatens to run rampant right now, notes Dave Nanda, crops consultant, Indianapolis. Nanda writes Corn Illustrated articles for Indiana Prairie Farmer  magazine and also is research director for 1stChocie hybrids, Milton, Ind.

He's spent the last two weeks walking and scouting Indiana cornfields. Some were planted to hybrids he sold. Many were competitor's hybrids. His philosophy is to help customers in general.

"The disease is certainly showing up on hybrids that are susceptible," Nanda says. "If the forecast for hot, humid weather over the next week or more holds, the disease will likely be off to the races."

It's not too late to spray fungicide in some cases, especially in later planted corn. However, so far Nanda has not found as much of the disease in corn planted in late May or very early June. He recommends that customers with those fields continue to scout. He also recommends that anyone who planted relatively susceptible hybrids to gray leaf spot scout.

It may no longer be economical to spray if the silks are all brown, indicating pollination is over and the ears are formed, especially if the disease is still below the ear lead. From here on out, adjustments that affect yield by the plant involve kernel size and test weight. By the time the gray lead spot shuts down the plant, those decisions should be made. The biggest threat would probably be that premature death would open up the plant for secondary infections of stalk rot.

Scout, scout, scout, Nanda says. That stakes are high. It's $30 or more per acre to spray a fungicide. Tha's 10 bushels of corn at $3 per bushel. But it;'s alos big-time losses if gray leaf spot knock out plants during or near pollination. The biggest thres tnow is likelyt to late-planted corn of susceptible hybrids.

About the Author(s)

Tom Bechman 1

Editor, Indiana Prairie Farm

Tom Bechman is an important cog in the Farm Progress machinery. In addition to serving as editor of Indiana Prairie Farmer, Tom is nationally known for his coverage of Midwest agronomy, conservation, no-till farming, farm management, farm safety, high-tech farming and personal property tax relief. His byline appears monthly in many of the 18 state and regional farm magazines published by Farm Progress.

"I consider it my responsibility and opportunity as a farm magazine editor to supply useful information that will help today's farm families survive and thrive," the veteran editor says.

Tom graduated from Whiteland (Ind.) High School, earned his B.S. in animal science and agricultural education from Purdue University in 1975 and an M.S. in dairy nutrition two years later. He first joined the magazine as a field editor in 1981 after four years as a vocational agriculture teacher.

Tom enjoys interacting with farm families, university specialists and industry leaders, gathering and sifting through loads of information available in agriculture today. "Whenever I find a new idea or a new thought that could either improve someone's life or their income, I consider it a personal challenge to discover how to present it in the most useful form, " he says.

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