Most Oklahoma wheat growers operate under tight profit margins, underscoring the need to make sound decisions about the application of wheat foliar fungicides.
“There is a lot of discussion about and advertisement of wheat foliar fungicides right now; some of the information out there is correct, and some is not,” said Jeff Edwards, Oklahoma State University Cooperative Extension small grains specialist.
In terms of major foliar diseases of wheat, Oklahoma producers should be watching for leaf rust and stripe rust.
Wheat leaf rust, also known as brown rust, is caused by the fungus Puccinia triticina. It is the most prevalent of all the wheat rust diseases. Small brown pustules develop on the leaf blades in a random scatter distribution. They may group into patches in serious cases.
Stripe rust is caused by the fungus Puccinia striiformis. Symptoms of stripe rust are long stripes of small yellowish orange pustules on the leaves. These pustules consist of masses of rust spores.
Bob Hunger, OSU Cooperative Extension wheat pathologist, said all wheat foliar diseases – including leaf rust and stripe rust – are at very low levels in Oklahoma as of the end of March.
“The extremely dry fall and winter limited development of these foliar diseases in Texas, from which spores are carried into Oklahoma to start these diseases in the spring,” he said. “However, recent moisture across Texas and Oklahoma will provide a more suitable environment for disease development.”
Hunger recommends producers start scouting their fields for signs of wheat foliar diseases, especially leaf rust, which will most likely be the primary wheat foliar disease in Oklahoma this year.
Producers need to remember that thorough coverage of the flag leaf is essential when treating with fungicides. That means 5 gallons per acre of carrier if spraying by air or 15 gallons per acre if using a ground rig. Use of a ground-rig sprayer is generally acceptable as long as narrow tires are employed.
“There are a great many products available,” Edwards said. “All of them are going to do a pretty good job. Some of the newer products are more effective, but they generally cost more.”
A listing of wheat foliar fungicides is available at http://osufacts.okstate.edu on the Internet. Use the Search function to access OSU Current Report No. 7668, “Foliar Fungicides and Wheat Production in Oklahoma – April 2008.”
Some producers also may be wondering what kind of a yield response they can expect from use of wheat foliar fungicides.
“Fungicides only protect yield potential that is already present,” Edwards said. “The key to predicting the likelihood of a yield response is the producer knowing the disease-resistance package of the varieties being grown.”
Studies by researchers at OSU and other institutions indicate that wheat foliar fungicides increase the yield of susceptible varieties by approximately 10 percent over time. On average, there is little yield increase on resistant varieties.