Wheat growers advised to scout for stripe rust; still time to apply fungicide

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COLUMBUS — While most wheat statewide is at the early grain fill stage of development, growers should still scout carefully for stripe rust, as some farmers have reported finding the disease in their fields, according to an Ohio State University Extension wheat researcher.

For those who do find the disease, there still may be time to apply a fungicide to fields planted with susceptible varieties, said Pierce Paul, who is also a plant pathologist with the Ohio Agricultural Research and Development Center.

Caution advised

Although the cool, dry conditions experienced in the region over several weeks this spring have reduced the risk of head scab having a negative impact on Ohio wheat, those same cool conditions are favorable for other diseases, such as rust.

Wheat crops can be affected by three types of rust: stem, stripe and leaf rust, with leaf rust being the most commonly found in Ohio. While levels of leaf rust and other diseases have been low thus far this season, some farmers have reported that stripe rust is developing in their fields, Paul said.

“Only fields planted with highly susceptible varieties are being affected,” he said. “Unlike leaf rust, which prefers warmer conditions, optimum of 68 to 77 degrees, stripe rust develops best under cool conditions.”

Effects

The issue is significant because stripe rust attacks the leaves of the wheat, which hinders the plant’s ability to absorb sunlight and reduces grain fill.

“Read fungicide labels carefully and pay attention to pre-harvest intervals before making a decision to apply a fungicide,” Paul said.

“Fungicides with full head emergence (Feekes 10.5) as the harvest restriction should not be applied, whereas other products cannot be applied later than 30 to 40 days before harvest.

“With harvest likely to begin somewhere between mid- and late June, most available fungicides are either already off-label or will soon be off-label.”

This as the USDA forecasts a yield of 47.6 bushels per acre nationwide, as of May 1, an increase of 40 percent from last year’s drought-ravaged harvest and the best since 2003, the federal agency said.

In Ohio, the forecast is for a yield of 63 bushels per acre, an increase from last year’s 58 bushels per acre, said Charlie Russell of USDA’s National Agricultural Statistics Service Ohio field office. The agency estimates the Ohio wheat crop will total 33.3 million bushels this year, he said.

“We’re expecting a larger yield this year even though the total production is down due to wet planting conditions last fall, which caused a lot of the winter wheat to not get planted,” Russell said.

Vigilance

With that in mind, it is important that growers scout their fields for disease, Paul said. Symptoms of stripe rust include pustules that are small and round and usually occur in groups, forming yellowish-orange stripes on the leaf surface.

“Occurring this early during grain fill, stripe rust may still affect yield if high levels develop on the flag leaf,” Paul said. “However, the warm, dry weather forecasted for the next few weeks will likely slow this disease down considerably.”

For more on wheat fungicides, including efficacy and harvest restrictions, download the Field Crops Disease fungicide table at www.oardc.ohio-state.edu/ohiofieldcropdisease/images/NCERA_184_Wheat_fungicide_table_2012.pdf.

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