Fusarium head blight, commonly known as scab, has noticeably increased in occurrence and severity in wheat and barley fields. A fungus, Fusarium graminearum, which may invade developing small-grain heads from flowering through kernel development, causes scab. Scab infection is favored by long periods of high humidity and high dew points that coincide with flowering and grain-fill. Those conditions were common in most areas of northwestern and west central Minnesota this year because of record rainfalls in June.

Growers with severe scab in their fields may take several steps to reduce their risk of harvesting grain with high levels of scabby kernels and DON (deoxynivalenol or vomitoxin).

• Before harvest, contact your insurance agent and the local Farm Service Agency to determine if any crop loss will be covered and to learn what insurance contracts require for loss coverage.
   
• Consider straight combining to minimize further development of the disease or DON production in the swath. Although swathing generally is used to bring down grain moisture levels faster than with straight cutting, swathing onto wet ground or getting rain on the swath could cause molding and further grain deterioration.
   
• Severely infected fields or portions of fields should be harvested and stored separately, if possible or practical. Scab severities and DON levels likely will be higher in portions of a field adjacent to drown-outs or in very low areas. Also, research at Michigan State University showed that the highest concentrations of DON were along field margins and in headlands in fields that had no problems with drown-outs. Use mechanical separation of scabby grain. Set the combine fan speed to blow out shriveled, diseased kernels that cause marketing and storage problems. Scabby kernels in the harvested grain may add to yield, but will diminish market price. Additionally, harvested grain can be further cleaned by gravity tables, which may reduce the level of scab enough to achieve top market grade and price in the cleaned sample.
   
• NDSU studies show that cattle and sheep mostly are DON tolerant. Hogs are sensitive to DON, even at one part per million (ppm) hog feed contamination. The toxin also can cause problems in horses, dogs and other single-stomach animals.
   
• Drying won’t reduce scab or DON levels, but drying prevents further fungus development. The moisture content of scabby grain going into storage should be about 12 percent. Scabby grain should not be co-mingled with good grain in storage.

The Food and Drug Administration has guidelines for DON levels in grain:

• 1 ppm for finished grain products for human consumption (many food processors and malt barley companies have stricter requirements)
   
• Cattle more than 4 months old: 10 ppm (providing the grain at that level doesn’t exceed 50 percent of the diet)
   
• Swine: 5 ppm (providing grain at that level doesn’t exceed 20 percent of diet)
   
• Poultry: 10 ppm (providing grain at that level doesn’t exceed 50 percent of diet)
   
• All other animals: 5 ppm (providing grain at that level doesn’t exceed 40 percent of diet)
   
• Straw from scab-infected fields should be suitable for cattle and sheep bedding, but is not recommended for horses.

Russ Severson, Extension Educator,
Polk and Red Lake Counties

and

Will Yliniemi, Extension Educator;
Hubbard and Becker Counties

Source for this article was Marcia McMullen, NDSU Plant Pathologist. NDSU Crop and Pest Report, 2005, Issue 13.