By Stephen Wegulo
Excessively wet weather this spring into early summer favored the development of Fusarium head blight (FHB, scab) in Nebraska wheat fields. The most severely affected fields are in the southeastern, south central, and southwestern parts of the state. The disease, caused mainly by the fungus Fusarium graminearum, is characterized by premature whitening or bleaching of wheat heads (Figures 1 and 2).
Figure 1. A Nebraska wheat field with severe Fusarium head blight.
Figure 2. Close-up of a wheat head bleached by Fusarium head blight
Bleached spikelets are sterile or contain kernels that are shriveled and/or appear chalky white or pink (Figure 3), referred to as Fusarium-damaged kernels, scabby kernels, or tombstones. Scabby grain usually contains the mycotoxin deoxynivalenol or DON, also known as vomitoxin. It belongs to a class of mycotoxins known as the trichothecenes and is harmful to humans and animals.
The following strategies are suggested for handling wheat grain from FHB-affected fields:
Harvesting. Increasing the fan speed on the harvest combine can remove some of the heavily infected grain, which usually is lighter and contains higher levels of DON than healthy grain.
Keeping scabby grain separate. Consider keeping grain from heavily affected fields or parts of fields separate. Incidence and severity of scab varies from field to field and within a field, depending on the variety planted and local environmental conditions.
Testing for DON. Presence of scabby grain does not necessarily indicate high mycotoxin levels and vice versa. Therefore, consider testing grain from affected fields for DON content. The sample submitted for mycotoxin testing should be representative of the entire truckload or bin of grain.
Cleaning. If the proportion of scabby grain is high, consider cleaning the grain with seed-cleaning equipment to remove or reduce scabby kernels. Cleaning does not eliminate DON as apparently healthy grain can have elevated concentrations of the mycotoxin. However, it significantly reduces levels of the mycotoxin by removing lighter, more heavily infected kernels.
Personal protective gear. When handling grain, wear appropriate personal protective gear such as masks to prevent inhaling mold spores and grain and chaff dust which can cause allergy and breathing problems. Wear latex/nitrile gloves to prevent absorption through the skin of DON and other mycotoxins that may be present in grain, chaff, or dust.
Figure 3. Scabby wheat grain (left) and healthy grain
Storage. Scabby grain should be stored at or below 12% moisture content. This will reduce the potential for deterioration due to mold growth during storage.
Marketing. If possible, DON-affected grain should be kept separate from healthy grain. The marketing strategy for DON-affected grain will be influenced by many factors including DON levels, cleaning and/or blending costs, and contract obligations with elevators. In general, elevator discounts are highest at harvest and increase with the concentration of DON above 2 ppm. Therefore, weigh the pros and cons, including economics, of deferring DON-affected contracted wheat in the hope that discounts will reduce with time. Deferring delivery also gives you time to clean and/or blend the wheat to improve quality.
Using scabby grain as seed. To prevent or reduce damping off and seedling blights, scabby grain should be thoroughly cleaned and treated with a systemic fungicide before being used as seed for next season’s crop.
Feeding. Scabby or DON-affected grain can be used as livestock feed. For recommendations on using feed contaminated with DON, consult the UNL extension publication Fusarium Head Blight of Wheat (EC1896). Straw from scabby fields can contain DON at concentrations that exceed 2 ppm. Therefore, straw from scabby fields should be tested for DON before using it for silage or bedding.