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Farmers struggle with blight

BY BEN MARKS | AUGUST 04, 2015 5:00 AM

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This year, Iowa corn farmers are facing a threat that may cost them a chunk of their yields and could translate to higher prices at the grocery store.

Although it is not as scary as it sounds, northern corn blight does do what it says, blighting unsuspecting corn before it can so much as blink, killing the leaves and leaving the corn stunted.

This year, Associate Professor Alison Robertson, an Iowa State University plant pathologist, said the blight is much more prevalent than in previous years and is widespread across Iowa.

“It’s the earliest in the growing season that we’ve seen northern leaf blight, and I’ve been here since 2004,” she said. “When the disease comes in earlier, it means it has more time for it to increase.”

Robertson said this is mostly because of Iowa’s recent weather.

For northern corn blight, the perfect weather is wet and cool. Although it may not seem like it with the Sun blazing down, July’s series of torrential downpours led to temperatures 2 degrees cooler than average.

Robertson said the temperatures, followed by high humidity, have transformed the fields of Iowa into the perfect place for the blight, and other diseases, to multiply.

The blight multiplies whenever corn leaves are wet for six hours or more, but sunlight drying the leaves will kill it.

Once it has grown, however, the blight works by infecting the leaves of a corn plant and killing the healthy green leaf tissue, leaving scars behind that aren’t able to photosynthesize. If enough leaves are damaged, the corn can’t get the sunlight it needs, and the ears will turn out stunted.

“When the disease is really severe, you might lose 30 to 50 percent of your yield,” Robertson said.

Mark Heckman, the vice president of the Corn Promotion Board and a farmer in southeast Iowa, said he has dealt with the blight before. While it happens every year, he said, this year, it has been much worse.

“It’s one of those things that happens every year when conditions present themselves,” he said. “If you see right now a lot of [crop-dusters] are flying, the conditions have been right and have been favorable for any fungus that can affect the yield of the crop.”

Leaf blight isn’t the only disease rearing its head in the damp conditions, however; Heckman said gray leaf spot has also been an issue.

Unfortunately there isn’t a cure for the blight once it has infected a plant; the only thing to do is have planes spray it with fungicide.

“It wouldn’t reduce the current number of the infected leaves, but it would help to prevent further infection,” said Ed Zaworski, a plant diagnostician at ISU’s Plant and Insect Diagnostic Clinic.

Recently, Zaworski said, officials have seen an increased number of plant samples with the blight being submitted.

Other than spraying, however, the only other option is to choose hybrids of corn that are resistant to the blight.


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