Ohio State Wheat Expert: Some Wheat Crops At Risk For Scab Development

May 21, 2015

By Tracy Turner

Southwest Ohio wheat growers with early flowering fields planted with highly scab-susceptible varieties are at moderate risk for Fusarium head blight development this week, said a wheat expert from the College of Food, Agricultural, and Environmental Sciences at The Ohio State University.

And while northern Ohio is at a high threat for Fusarium head blight, also called head scab, growers there don’t need to panic because much of their wheat is probably not at the critical flowering stage yet, said Pierce Paul, an Ohio State University Extension wheat specialist.

Much of Ohio’s wheat has progressed considerably over the last week and is now heading out in some fields, said Paul, who is also a plant pathologist with the Ohio Agricultural Research and Development Center.

OSU Extension and OARDC are the outreach and research arms, respectively, of the college.

“Some fields in southern Ohio as well as those planted early or with early maturing varieties in the central and northern parts of the state are at the flowering growth stage or will be flowering by the end of this week,” he said. “Scab and vomitoxin contamination of the grain is the biggest concern for wheat growers during this point in the growing season.”

This information is gleaned using a regional online assessment tool to determine head scab development risk. The Fusarium Risk Assessment Tool available at the Fusarium Head Blight Prediction Center website, wheatscab.psu.edu, helps growers assess the risk for scab and to determine whether a fungicide application at flowering is warranted for scab control, Paul said.

“Wheat growers need to be aware of the risk but not panic,” he said. “Growers with fields grown with very susceptible wheat varieties in the flowering stage in areas that the prediction center says has favorable conditions for scab development may want to consider treating their fields with fungicide.

“But those growers who’ve planted resistant varieties face less of a scab problem.”

Head scab is of concern for growers during flowering, which is when wheat heads are most susceptible to the scab fungus and infection is favored by warm, wet or humid conditions, Paul said.

“The ideal time to apply these fungicides is at flowering, but applications made up to six days after flowering may also provide good levels of scab and vomitoxin control,” he said. “If your field is flowering, planted with a very susceptible variety and is located in an area with moderate-high risk, consider applying Prosaro or Caramba at full label-recommended rates.”

Scab is the most economically important wheat disease in Ohio because it affects wheat in multiple ways, Paul said. Scab can cause vomitoxin contamination of the grain, making the grain unfit for marketing and unfit for human or animal consumption.

There is some good news for wheat growers, however. Thanks to favorable weather in May, some early foliar diseases such as powdery mildew and Septoria tritici leaf spot haven’t been a problem for most wheat growers so far this year, Paul said.

But extended cool weather and the recent rainfall and high relative humidity could cause that to change, he cautions.

“Septoria in wheat typically spreads from the lower to the upper leaves of the plant during rainy conditions and develops best when temperatures range between 50 to 68 F.

“Powdery mildew can also develop under cool conditions with high relative humidity.”

Growers that have planted highly susceptible varieties will need to walk their wheat fields and scout for any indication of disease, Paul said.

“For those growers with susceptible varieties, if the weather conditions become favorable, such as rainy, cooler temperatures, a fungicide can be applied to prevent the diseases from reaching the flag leaf or the uppermost leaf of the plant before grain fill,” he said.

Septoria tritici leaf spot typically first appears on wheat plants on the lower leaves as yellowish flecks that later develop into irregularly shaped brownish-gray lesions with dark-brown to black spots in the center, Paul said.

Cooler temperatures combined with relatively high humidity generally cause powdery mildew, he said.

Source: purdue.edu