Wheat scab starting in Mid-south

In Delta Farm Press

This is a nice time of the year in the Mid-South. Temperatures are warming, the rains are starting to become less frequent and dark-green fields of grain are waving in the breeze in parts of the country where farmers still sow winter wheat.

Unfortunately, farmers in Louisiana and some parts of Arkansas have begun observing fields where the grain is not so green and, in fact, is beginning to show the telltale signs of bleaching that generally accompany infections by Fusarium head blight or scab.

“What you’ll see is the wheat looks to be maturing when it’s not supposed to be mature,” says Paul “Trey” Price, field crop pathologist with the Macon Ridge Research Station near Winnsboro, La. “You’ll see bleaching of the heads. This is not normal. That’s the result of infection by the pathogen that causes Fusarium.

“It also causes shriveled seed, and I’ve picked some out of the field here,” said Price, referring to a set of plots where scientists are screening wheat varieties for possible resistance to scab. “This is milk stage wheat. It looks like it is supposed to be maturing, but it’s not.”

Price was speaking at the Wheat and Oats Field Day held at the Macon Ridge Station on April 22. The field he was referring to had been inoculated with wheat scab through a sprinkler system, but a number of fields in central and northeast Louisiana are showing symptoms of the disease, as well.

“If you look at this field out here, you can see that the wheat is maturing,” said Dr. Price, pointing to an adjacent field at the Macon Ridge Station. “It’s not supposed to be maturing; that’s milk stage wheat. This is what’s it’s going to look like from the turn row, except hopefully not this severe.”

Outbreaks variable

Dr. Price said outbreaks of wheat scab can be variable, having been reported in the Great Plains, central U.S., Mid-South and Southeast over the last 20 years. Losses have been reported as high as 20 percent in isolated fields with susceptible varieties.

“Some losses have been reported up to 80 percent, so it can get bad under the right conditions,” he said. “Those are wet, warm weather during flowering. The fungus may infect wheat from flowering up to harvest with the most devastating infections occurring during flowering.”

Price and Boyd Padgett, field crops pathologist and regional director at the Dean Lee Research Station in Alexandria, La., said they had received multiple reports of wheat scab or Fusarium head blight from producers and consultants during the last two weeks of April which corresponds to the flowering period for many fields in Louisiana.

Symptoms of the disease will first appear ten to 14 days after flowering as bleached heads. Upon closer inspection, affected wheat heads will usually have infected kernels showing the characteristic bleached appearance with pinkish/salmon/orangish coloration along the glumes.

“This coloration is millions of microscopic spores of the fungal pathogen. There are usually healthy kernels along with the diseased kernels on the same head,” says Padgett. “In extreme cases, however, the entire head may be infected. At harvest, affected seed will be shriveled, off color, and much lighter than healthy kernels and are referred to as ‘tombstones.’”

Plant breeders have two types of resistance they can try to use to fight scab. One is Type 1 resistance that prevents the plants from becoming infected with scab. Type 2 prevents the disease from moving up and down the plant once it becomes infected.

For the rest of the story, along with a video, go to Delta Farm Press.

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