June 13, 2002 | By: Laura Skillman
PRINCETON, Ky.

Kentucky's wheat fields are showing signs of head scab, a disease that shrivels the kernel, reducing yields and lowering test weights.

The disease, Fusarium head blight, also can produce a toxin that limits a grower's options on selling the product. If the grain is too high in vomitoxin, grain elevators and millers will refuse to buy it leaving farmers few options, said Don Hershman, University of Kentucky Extension plant pathologist. Depending on toxin level, contaminated grain may be suitable to feed to some animals but not to others who may be highly susceptible to the toxin.

This year's outbreak of the disease is variable, Hershman said. This is the highest incidence of the disease since 1991 when head scab caused tremendous problems in Kentucky wheat fields as well as in most soft red wheat growing regions of the country. In the past three years, there has been little to no signs of scab in Kentucky's fields, he said.

"This year is a third to a half as bad as it was in 1991," he said.

Wheat is most susceptible to the disease during flowering. Wet, warm, humid weather makes the perfect conditions for an outbreak of the disease. Kentucky was right on the fringe in terms of temperatures this year, Hershman said. That probably allowed for many crops to escape infection.

"If there's moisture and the temperatures are appropriate, then the spores are going to be blowing around everywhere," he said.

Lloyd Murdock, UK Extension agronomist, said he expected to see scab outbreaks this year because of all the rain.

"In talking to farmers it is pretty well everywhere," he said. "Everybody's got it. Some of the infections run as low at 5 percent with yield losses below that. Some are seeing over half the heads affected by scab and are estimating a 25 percent yield loss. We began to see it May 16 and by a week later, it was very evident."

Hershman also noted that based on large-scale on-farm plots, there is little difference between no-till wheat versus tilled. The incidence was statistically the same while severity may be a little worse in no-till, but the environmental advances of no-till production along with time and equipment savings more than offset it, he said.

Over the years, there has been concern in no-till planting wheat into corn stubble because the disease organism survives in corn stubble.

Theoretically it makes sense, but that is not the case based on 20-acre plots on three locations that were planted on the same day with the same variety and treated the same, Murdock said. Estimated yield loss in the three locations showed no differences between the two production methods, he said.

"I don't know of any other experiment like this around and our experience shows us there is really no difference," Murdock said.

The results aren't a surprise, because weather is the main factor, Hershman said. "There's no question corn stubble is the main source of the fungus, but in our state there are a lot of small corn fields and in areas where wheat is also grown. This fungus is airborne and if I till and you no-till and we are just 200 yards down the road, those spores are blown in. They are everywhere."

Few varieties are highly resistant to the disease. Research on this disease is ongoing in Kentucky and many other states through the U.S. Wheat and Barley Scab Initiative. Hershman, who is based at UK's Research and Education Center in Princeton, said the main goal is to develop resistant varieties, but in the short term fungicide controls are being studied.

The fungicide effort is being replicated in 20 states. As of yet, no dramatically effective treatments have been found, Hershman said.

Another factor with fungicide use is that the disease is not a problem every year, so Hershman said he does not foresee recommending the use of a fungicide on an annual basis. Presently, there is no fungicide labeled for use late enough in the growing season.

UK wheat breeder Dave Van Sanford is working to develop a scab resistant variety. It takes a tremendous amount of effort he said, with research being done both in greenhouse and field settings.

Van Sanford's efforts have seen progress and he anticipates releasing a variety this fall that has shown to have good resistance in research trials.

Other research on the disease is being conducted by Dennis Tekrony who is studying the effect of the fungus on seed quality, and Lisa Vaillancourt who is trying to develop a mutant to the fungus, Van Sanford said.

"Our overall goal is to find better control of the disease," he said.

Farmers can help remove some of the damaged wheat by turning up fan speed and blowing the light chaff out of the combine at harvest but it will not eliminate it, Murdock said. There is a quick test available to determine toxins, and farmers who are interested in testing grain prior to marketing should check with their buyer for more information.

Contact: 

Don Hershman and Lloyd Murdock, (270) 365-7541 and Dave Van Sanford, (859) 257-5811