Mixed bag: Rain brings hope, threat of disease to wheat crop

Writer: Steve Byrns, 325-653-4576, s-byrns@tamu.edu
Contact: Dr. David Drake, 325-653-4576, drdrake@ag.tamu.edu

SAN ANGELO – Above average rainfall has given farmers a crack at a bumper wheat crop, but a Texas AgriLife Extension Service expert warns producers to be vigilant and not lose it through disease brought on by the favorable conditions.

Bad News: the yellow-orange spots on these wheat leaves near Brady show the initial signs of leaf rust. (Texas AgriLife Extension Service photo by Dr. David Drake)

“Recent rains in the Southern Rolling Plains and throughout West Central Texas have increased the prospects of getting an average or even an above average wheat crop this season,” said Dr. David Drake, AgriLife Extension agronomist at San Angelo. “Unfortunately, the moisture also creates conditions ripe for fungal wheat diseases.

“Several fungal diseases attack the leaves of wheat and can quickly devastate grain yields. Leaf rust is one of the worst. It’s been confirmed in South Texas and is spreading rapidly north as the season progresses.”

Drake said the only known way to combat leaf rust is to plant resistant varieties or apply a preventative fungicide. Since the crop is fast approaching maturity, applying fungicide is now the lone alternative.

“Growers need to scout their fields every few days by walking out into the crop and looking closely at the plants,” Drake said. “Leaf rust begins as small yellow spots on the leaves. Advanced infestations will have larger spots covered with powdery rust-colored spores which give the disease its name.”

Drake said the spores are spread by wind or water and soon infect other leaves and plants.

Stripe rust, another fungal disease, is similar in appearance to leaf rust but develops stripes across the leaf instead of spots. Cool temperatures contribute to stripe rust and so far, he said it’s not been found this year.

“If producers do find rust in wheat, then they need to evaluate the condition and growth stage of the crop, its potential yield, the grain price and the cost of the treatment before proceeding,” Drake said. “That’s because a fungicide application will only protect the crop that’s there. It won’t compensate for a poor stand, drought conditions or low soil nutrients.

“If it is decided that the disease is present and there is a good yield expectation, then the crop is best protected as the flag leaf is emerging.” he said.

Research has shown that the flag leaf, the leaf just below the head, can contribute up to 85 percent of the grain, Drake said. He said the best time to spray is when the flag leaf is emerging on up to the time of its full emergence. Later spray applications are not as effective.

“Most of the wheat in our area is very rapidly approaching this stage,” he said. “There are several fungicides that, if applied correctly, will provide very good control of both leaf and stripe rust. Always read and follow label directions no matter what you use. And hopefully, the rains will continue and the crop will exceed last fall’s low expectations.”

For more resources on identifying and controlling wheat diseases, see:
http://varietytesting.tamu.edu/wheat/index.htm and
http://amarillo.tamu.edu/amarillo-center-programs/extension-plant-pathology/wheat-publications/wheat-disease-fact-sheets/ .

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