WOOSTER, Ohio - Ohio State University researchers are trying to stay one step ahead of head scab, a fungal disease of wheat that can cause severe yield and economic losses.
University plant pathologists have developed a head scab forecasting system, mathematical models that analyze weather patterns from various weather stations throughout Ohio to predict the likelihood of a head scab outbreak. The system, developed last year, is over 80 percent accurate in predicting the risk of head scab during the growing season, said Pat Lipps, an Ohio Agricultural Research and Development Center (OARDC) plant pathologist.
"Head scab outbreaks are so closely related to weather patterns that it's been found that we can use those patterns to predict the disease. So the data from the model is used to assess the risk of head scab and then we put our common sense to work," said Lipps. "At this point in time, the model is designed to provide information and not to be used as a base for any management practices."
The head scab forecasting system was developed using 50 location-years of weather data throughout the United States, including such states as Ohio, North Dakota, Kansas and Missouri. The system assesses head scab risk based on temperature and relative humidity.
"The temperature threshold level for head scab is 60 degrees and if you get temperatures above that with plenty of rain, it's enough to generate activity," said Lipps.
Risk assessment is based on the results of two models. The first model predicts the probability of head scab seven days prior to the flowering of the crop by looking at the duration of precipitation and the number of hours temperature is between 60 and 86 degrees, the optimal time for spore development. The second model predicts the probability of scab seven days prior to flowering and 10 days after flowering by looking at average temperature and overall relative humidity. It is during this time that the disease is most likely to develop.
The researchers were pleased with the outcome of last year's predictions using the forecast model. "The model came out pretty accurate last year. It accurately predicted the probability of head scab for two-thirds of the state," said Lipps. "The good thing is we didn't have any major epidemics so I think we came out pretty good."
Head scab infections in Ohio during 2001 were low. Average bushel per acre was 67 compared to 72 bushels per acre the previous year. Only one to two percent of the 900,000 acres of wheat grown in the state was lost due to head scab and other factors. "We had plenty of rain, but the temperatures stayed below 60," said Lipps. "If it would have been five degrees higher, we would have had a major epidemic on our hands."
Areas that suffered the most loss to head scab included central and northwest Ohio. Counties affected included Licking, Fairfield, Pickaway, Franklin, Delaware, Union, Clark, Wood, Lucas, Fulton, Henry, Williams, Defiance, Paulding and Van Wert.
The researchers plan to use the forecasting system again this year to assess head scab risk, and researchers will increase the number of weather station locations from six to 20 to collect more accurate data.
Head scab, also known as fusarium head blight, 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.
Head scab epidemics can be devastating. According to a recent 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.
"One thing to remember is that the threat of scab is an annual event, but it's a disease to reckon with and it's no picnic when it happens," said Lipps. 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.
For more information on the head scab forecasting system, log on to http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/2001wheat.htm.