wheat rust

Wheat rust spores ride in on a south wind and can be devastating to crop prospects.

Wheat producers across northern Oklahoma need to make judgments about whether or not to apply a fungicide, and quickly for their 2008 wheat crop.

As of April 28, leaf rust was present across central and northern Texas in moderate levels and was beginning to appear at increasing levels across central and southern Oklahoma, according to reports by Oklahoma State University’s Division of Agricultural Sciences and Natural Resources.

Most of the wheat in southern Oklahoma was headed and much of this is currently flowering, which is beyond the time when fungicide should be applied.

Heads were emerging or were nearing complete emergence in wheat across northern Oklahoma.

“Application of a fungicide to this wheat needs to be done soon so it is applied prior to the start of flowering as indicated by the emergence of the anthers,” said Bob Hunger, Oklahoma Cooperative Extension Service wheat pathologist.

Wheat in the state’s panhandle was a bit behind that seen across much of northern Oklahoma.

“Rust inoculum is being spread northward and producers across northern Oklahoma need to consider applying a fungicide to protect their yields,” Hunger said.

Fungicides will provide protection for a three-week period, with full protection the first two weeks and partial protection during the third week.

“It’s critical to try to apply fungicide so that protection is afforded while the wheat is going through the stages of heading-out, flowering and milk,” Hunger said. “Applying the fungicide too early can mean a lack of protection as the wheat is flowering, but applying the fungicide too late can mean protection after the leaf rust is not much of a factor.”

Many years of fungicide training trials have indicated that the best time for application ranges from the flag leaf fully emerged to heads being slightly emerged from the boot.

Leaf rust has the potential to decrease yield and is most damaging when leaf rust is severe early.

“Leaf rust severity on flag leaves of around 65 percent in the flowering stage can reduce grain yield by as much as 30 percent to 35 percent,” said Art Klatt, OSU professor of plant breeding and genetics. “The same level of infection when wheat is in the dough stage, however, generally will reduce yield by 10 percent or less. Hence, if you’re growing a variety susceptible to leaf rust with excellent yield potential, consider using a fungicide to protect that potential.”

A key point to remember is that a fungicide will only protect yield potential and will not restore yield once it has been lost to disease. Thus, it is important to provide protection with a fungicide before the disease is well established on the wheat.

“This is always difficult because most producers want to wait until they know for certain their wheat has the disease before spending money on the fungicide,” said Jeff Edwards, OSU Cooperative Extension wheat agronomist.

Producers looking for additional information on fungicide applications for control of foliar diseases in wheat should contact their local OSU Cooperative Extension county office and ask for Current Report No. 7668, “Foliar Fungicides and Wheat Production in Oklahoma.”

The OSU report is also available at http://osufacts.okstate.edu on the Internet.

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