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Scout for Fusarium Head Blight (Scab) symptoms

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What is Fusarium Head Blight (FHB)?

FHB, also called scab or head blight, is a fungal disease caused by several species in genus Fusarium: F. graminearum, F. pseudograminearum, F. avenaceum and F. culmorum. The pathogen survives on crop stubble of wheat, barley, and corn. Wind-blown spores can travel up to 100 miles and enter a field that way. Infected seed is another avenue to introduce the pathogen. Within a field, the disease is spread by rain splash and wind. The critical window for infection occurs during flowering. Moist environmental conditions caused by timely rains, irrigation, fog, and long dew periods promote infection at warm temperatures of 65 - 85° F.

A big concern with FHB is the production of mycotoxins that contaminate the grain. Deoxynivalenol (DON), also known as vomitoxin, is of primary concern and subject to regulatory limits by the U.S. FDA. There is a 1 ppm limit for DON in all finished wheat products that may be consumed by humans. Limits of 5-10 ppm have been set for animals. There is a zero tolerance for DON in malt barley. Mycotoxins levels in the grain will remain unchanged for years in storage.

What symptoms of FHB should I look for?

(See pictures) Symptoms of FHB express several weeks after infection during the soft to hard dough stage. Look for partially bleached heads and a dark discoloration of the peduncle (stem below the head). Pink or orange spore masses may develop on infected spikelets under moist conditions. Infected kernels are shriveled, chalky, white and white (“tombstones”).

Am I at risk for FHB?

There are several factors that increase the likelihood of FHB in your crop:

  • A history of FHB in previous crops
  • Cereal-heavy rotations, including corn.
  • Corn crop grown nearby
  • Moist environmental conditions during flowering: 3+ rain or irrigation events from anthesis until 3-5 days post-anthesis dramatically increase FHB risk.
  • Susceptible varieties.

What steps can I take now if I have FHB in my crop?

  • Stop irrigation in fields with symptoms of FHB.
  • Harvest fields with FHB separately and avoid mixing contaminated and non-contaminated grain.
  • You can remove lightweight tombstone kernels by adjusting screen size and airflow. This can reduce DON levels in seed lots by 50% or more. Care should be taken not to blow infected grain in the field, as this will be a source of inoculum in following crops.
  • Store the grain at cool temperatures and humidity levels below 12%.
  • Test grain for mycotoxins before feeding it to livestock. Consult an animal specialist before feeding the grain.

The Veterinary Diagnostic Laboratory at North Dakota State University offers tests to determine mycotoxin concentrations ($175 charge per sample).

Where can I find more information?

 

Picture Captions

Figure 1. Partially bleached heads are a good indicator that the plant is infected with FHB. (Picture credit: Emmanuel Byamukama; Source: Bugwood.org)

Figure 2. Pink or orange spore masses may develop on infected spikelets under moist conditions. (Picture credit: Craig Grau; Source: Bugwood.org)

Figure 3. Shriveled, white, chalky FHB-infected kernels (right) are descriptively called “tombstones”. (Picture credit: Photographer unknown; Source: MSU Extension MontGuide MT200806AG)

 

Please don’t hesitate to email (uta.mckelvy@montana.edu) or call (406-994-557) if you have any questions. I’m here to help.

Best,

Uta McKelvy, Extension Field Crop Pathologist