Head Scab Risk Low in Ohio

June 10, 2002

WOOSTER, Ohio - Much of Ohio's wheat crop may have escaped the risk of head scab disease, a bright spot in what's shaping up to be a rather dismal growing season for crop producers.

Pat Lipps, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center, said that predictions for head scab development throughout southern and central Ohio have been rated low or moderately low.

The current area of concern is in counties throughout the northwest portion of the state, where heavy rains have saturated heavy clay soils, creating conditions conducive for head scab development. Lipps said it could be a week before a definitive determination is made as to whether or not the crop in that region will develop the economically damaging disease.

"So far, everything has been good for us. Most of the state has made it through the critical period," said Lipps. "The northwest corner of the state is where we are concerned right now. Basically recent warm weather and high levels of precipitation have made it favorable for infection and if that trend continues, there could be a possibility of scab." Counties being watched for head scab risk include Fulton, Williams, Defiance, north Henry, north Wood and parts of Sandusky.

The assessment of head scab risk was made using mathematical models developed by Ohio State crop specialists that use weather data to determine the probability of disease development. Researchers collected data from 15 weather observation stations in Ohio, southern Michigan and eastern Indiana.

One model analyzes the duration of precipitation in hours and the number of hours the air temperature is between 60 degrees and 86 degrees Fahrenheit for seven days prior to flowering. It is during this time when the fungus develops spores. Lipps said the model has been 78 percent accurate in determining low level of disease development.

The second model calculates the number of hours when the air temperature is between 60 degrees and 86 degrees Fahrenheit for seven days prior to flowering, when the relative humidity is above 90 percent and when the air temperature is between 60 degrees and 86 degrees for 10 days after flowering. The model addresses the time when the fungus develops spores, when infection occurs and when disease develops. It has proven to be 84 percent accurate in determining economic levels of disease development.

"We talked to a plant pathologist in Pennsylvania recently, and they are very close to our predictions," said Lipps. "Indiana is about the same as Ohio, and Michigan right now is entering a point of concern. Pathologists in Ontario (Canada) are very concerned about head scab right now, because the same sort of showers hitting northwest and southern Michigan are going right over Ontario." Head scab, or Fusarium head blight, can be devastating for wheat producers. The disease is likely to occur when warm, wet weather persists during the crop's flowering stage in May and June. The disease infects the wheat heads, causing shrunken, lightweight kernels, thereby reducing the quality and feeding value of the grain. The fungus that causes the disease also produces a chemical in the infected grain called vomitoxin that is toxic to livestock and humans.

According to a North Dakota State University study, United States direct and indirect economic loss from head scab from 1998-2000 was estimated at $2.7 billion. Ohio's losses were estimated at over $315 million for the three-year period. Ohio's last major head scab epidemic occurred in 1996 when yields dropped to 39 bushels per acre. Farm income losses alone were estimated at $180 million.

Northwest Ohio is home to the highest wheat producing counties in the state. "That's where we grow most of our wheat and when we have a risk up there of head scab, it has a bigger impact on our total production," said Lipps.

The crop throughout the northern regions of Ohio is now in flower. Approximately 10 days after all counties have wheat in flower, researchers are expected to have the forecasting models for the entire state completed.

Ohio ranks seventh overall among all winter wheat-producing states in the United States and produces some of the highest quality soft red winter wheat sought after by millers and bakers.

For more information on the head scab forecasting system, log on to http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/Scab%20forecasting%20webpage02.htm.

Author(s): 
Candace Pollock
Source(s): 
Pat Lipps