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Corn farmers need to scout for Southern rust

News Release Distributed 07/14/14

WINNSBORO, La. – Corn farmers should be looking for a damaging fungal disease, Southern rust, which has been found recently in Louisiana.

“Some years we see it. Some years we don’t,” said Trey Price, plant pathologist at the LSU AgCenter Macon Ridge Research Station, adding that the disease is not always a problem for Louisiana growers.

Price said a moderate to heavy infestation has been found in a fungicide trial at the LSU AgCenter Dean Lee Research and Extension Center in Alexandria and in commercial fields in southwest and south central Louisiana. Lighter disease levels have been observed in northern Louisiana.

He said the potential yield losses in late-planted corn could be significant enough to be critical with this year’s low prices.

Corn planted in mid- to late April is more susceptible to the disease. “If corn is in the milk to dough stage right now, you should be scouting for it,” he said.

He said variety trials at the Dean Lee Center may help reveal which hybrids have resistance. Fungicides may help reduce the effects – if an infected crop has yet to reach the dent stage – with strobilurin and triazole fungicides having activity. After the dent stage, he said, fungicides likely will not provide an economic benefit.

Fungicide applications, if warranted in late-planted corn, will slow disease development and preserve yield, he said.

The disease infects leaves and interferes with photosynthesis, resulting in reduced yield from decreased kernel development, he said. The disease usually starts on lower leaves and spreads upward.

Unlike common rust disease, the orange spores are usually only found on the tops of leaves, Price said, and common rust spores are more reddish.

“Warm, humid conditions with consistent rainfall are ideal for Southern rust,” Price said.

The start of corn harvest is three to six weeks away, he said.

Bruce Schultz

Last Updated: 7/14/2014 9:58:08 AM

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