Head Scab and Vomitoxin in Wheat

Each year during grain fill, maturity, and harvest, many questions begin to surface about head diseases. Portions of bleached heads surely get everyone’s attention as the crop begins to show symptoms of Fusarium Head Scab and/or Blight. Infections of this disease happen during flowering and are intensified under wet humid conditions. Weeks later, as grain fill takes off, a visual assessment tells the story of the disease severity. The bleached spikelets are often sterile or contain shrunken and shriveled grains. Head scab is a fungal pathogen from the Fusarium family, the same family that can cause diseases in corn. The head scab fungi itself is comprised of over 12 different species of fungal pathogens. Some considerations to help manage this disease are;

1. Crop rotation, it is preferable for the previous crop to not have been a grass species which includes corn and most small grains.
2. Variety Resistance, variety selection and genetic resistance to head scab can be an effective tool to minimize this disease.
3. Fungicides, applying the proper type of fungicide at the proper timing (flowering) can suppress head scab, but not eliminate it.
4. Tillage, the fungal pathogens that cause this disease overwinter on residue. They survive particularly well on the surface. Burying residue via tillage can be effective in reducing the inoculum levels in the field.

Vomitoxin

Vomitoxin is one type of many mycotoxins that are toxic to livestock and humans. Vomitoxin can cause dockage beginning at 2ppm at most elevators, or even rejecting the load for levels reaching 5ppm and above. Head scab not only causes yield losses, but also can become more serious when trying to market grain infested with vomitoxin. Dockage & rejection standards for grain buyers may be even more strict for farmers growing soft white wheat.

Vomitoxin is caused by fusarium head scab, and that’s it. Diseases, insects, and hail do not cause fusarium head scab or contribute to its severity. So, you must have head scab to get vomitoxin. However, just because you have head scab does not mean you will have high vomitoxin levels. Some years or fields will have higher or lower vomitoxin levels given the same percent head scab infestation. Head scab severity can be used to predict if vomitoxin will be an issue. Typically, head scab infestations of less than 10% are not likely to contain vomitoxin levels greater than 2ppm. An individual kernel analysis produced the following vomitoxin levels based on kernel appearance:

Normal: 1-1.5 ppm

Shriveled: 2-5 ppm

Shriveled and pink: 175 ppm

Vomitoxin, sometimes referred to as DON, is a fungus that produces within the infected kernels. This fungus only grows at grain moisture 22% and above. It is recommended that wheat grain with vomitoxin be stored at or below 12% moisture. Experts suggest that if the infected wheat is properly stored, the storage life is only slightly less than normal wheat.

Troubleshooting other diseases

Fusarium Head Scab can be confused with other wheat diseases & ailments. Septoria glume blotch and other head diseases can also cause discoloration of the spikelet, but is usually accompanied by black specks or striping which head scab does not have. Typically, environmental, insect, and disease ailments that cause premature plant death result in a bleached stem and head. Head scab rarely bleaches the entire head, but it remains on a green stem. Still, some diseases can cause a bleached head on a green stem, but they are typically bleaching the entire head with most heads appearing that way. Head scab usually appears randomly across the head infecting some but not all spikelets.

^Sources:

1. ^{North Dakota State University. http://www.ag.ndsu.edu/pubs/plantsci/pests/pp1302w.htm}
2. ^{Michigan State University. http://fieldcrop.msu.edu/sites/fieldcrop/files/FHB08.pdf}
3. ^{Compendium of Wheat Diseases, Second edition. The American Phytopathological Society}

This information may have been accumulated from publicly available sources outside of Dyna-Gro Seed, or its affiliates. Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Dyna-Gro® is a registered trademark of Loveland Products, Inc. Featured logos are service/trademarks of their respective owners.