June 21, 2013

	Figure 1 (left). A wheat head partially bleached by scab in a grower’s field on June 19. Figure 2 (right). A wheat head entirely bleached by scab (left) and a healthy head in a growers field on June 19.

Some wheat fields in eastern Nebraska have been affected by Fusarium head blight (scab) due to rains occurring before and during flowering. Incidence and severity of the disease vary from trace to moderate and some fields or parts of fields are more affected than others. Growers are advised to inspect their fields for scab.

Scab causes premature bleaching of heads (spikes) of small grain cereals. In wheat, the bleaching starts with one or more spikelets on a head (Figure 1) and can continue until the entire head is bleached (Figure 2). The color of the bleached heads varies with wheat cultivar and can range from white (Figure 2) to brown (Figure 3). In a disease-favorable growing season, numerous spikes can be seen randomly scattered in the field (Figure 3). Bleached spikelets are sterile or contain shriveled and/or chalky white or pink kernels known as Fusarium-damaged kernels (FDK), scabby kernels, or “tombstones” (Figure 4). Kernels that appear to be healthy also may be infected, especially if infection occurred late in kernel development. Infected kernels contain mycotoxins, primarily deoxynivalenol (DON).

If moderate to high levels of scab are found, the following strategies can be used to handle scabby grain:

• Harvesting. Increasing the fan speed on the harvest combine can remove some of the heavily infected grain, which usually is lighter 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 even within a field depending on the variety planted and local environmental conditions.
   

• Figure 3. Part of a wheat field showing randomly scattered heads bleached by scab at the UNL Agricultural Research and Development Center near Mead on June 19. Figure 4. Scabby grain (left) and healthy grain.

• Testing for DON. Scabby grain is likely to contain the toxin deoxynivalenol (DON) and to a lesser extent the toxin zearalenone. However, presence of scabby grain does not necessarily indicate high toxin levels and vice versa. Therefore, consider testing grain from affected fields for DON concentration. The sample submitted for toxin 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.
   
• Personal protective gear. When handling grain, wear appropriate personal protective gear such as masks to prevent inhaling mold spores and grain dust which can cause allergy and breathing problems.
   
• Blending scabby grain with healthy grain. Fusarium-damaged grain can be blended with healthy grain in proportions that will lower DON concentration to levels below regulatory/advisory limits. These limits are 2 ppm in grain and 1 ppm in finished wheat products for human consumption.
   
• Storage. Scabby grain should be stored at or below 12% moisture content. This will reduce the potential for deterioration during storage. Cool the grain by aeration soon after placement in storage and continue cooling periodically as outdoor temperatures decline until the grain is at approximately 25oF. Storing grain at or below 12% moisture prevents grain deterioration that can result from fungal activity if moisture content were higher. It does not reduce the amount of DON in the grain.
   
• Marketing. 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 time to clean and/or blend the wheat to improve quality.
   
• Feeding. Scabby or DON-affected grain can be used as livestock feed. Some livestock are more sensitive to DON than others. For recommendations on using feed contaminated with DON, consult the UNL extension publication Fusarium Head Blight of Wheat (EC1896).
   
• Using scabby grain as seed. To prevent or reduce seedling blights, scabby grain should be thoroughly cleaned and treated with a systemic fungicide before being used as seed for next season’s crop.

Stephen Wegulo
Extension Plant Pathologist