Wheat Scab:
What is it? How To Manage It.

Fusarium Head Blight, also known as wheat Scab, can be a serious problem in North Carolina. The fungus results in lower wheat yield and test weight. Scab also results in toxins in the harvested grain. The most common Scab toxin is “DON” or vomitoxin. When DON reaches 2 parts per million the grain is no longer fit for human consumption and can not be sold to a flour mill. When DON reaches 5 parts per million it is no longer fit even for swine feed. In 2003, estimates were that DON levels in North Carolina were so high, that 50% of the wheat harvest was unfit for human consumption.

Scab Management
Sadly, there are no single management practices that will guarantee that Scab will not develop and there are no effective foliar fungicides that will control Scab. However, there are important steps wheat producers can take, that when added together can greatly reduce the likelihood of a major Scab outbreak. These steps are outlined below:

Plant Only High Quality Seed: Fusarium can be a seed borne disease. Seed from fields that had scab infections should not be used for plant back. If seed is contaminated with Scab and must be used for planting, we recommend that it be treated with a fungicide or a combination of fungicides (e.g. Dividend Extreme, RaxilXT, or Raxil-Thiram).

Plant Wheat Varieties With Resistance to Scab: Research at Virginia Tech and NC State University have shown that we do have some varieties that are “moderately-resistant” to Scab. North Carolina producers can find these varieties at: www.smallgrains.ncsu.edu/Varieties/VarietyCharacter.pdf and should give these varieties serious consideration.

Tillage and Rotation: The primary sources of the disease are corn and/or wheat residues left on the soil surface from previous crops. Thus, conventional-tillage practices that bury these residues are the most effective means of controlling Scab. Conversely, no-tillage wheat planted into corn stubble, or no-tillage wheat planted after double-cropped soybeans when wheat straw is still present from the previous crop are at the highest risk to Scab.

For producers who wish to plant no-tillage wheat, the best rotation might be to follow full-season soybeans, or to follow cotton (as long as it was not planted minimal-tillage into standing wheat straw that is still present). If producers must plant no-tillage wheat after corn, anything they can do to mow, chop, grind, and/or shred the corn stalks may help reduce the risk of Scab at least a little. Whether planting conventional- or no-tillage wheat, rotations that have wheat following crops other than corn or double-cropped soybeans will be the most effective in reducing Scab infestations.

Force Heading to Occur Over a Series of Spring Dates: Scab is spread by warm moist weather, and rain splashing off of infected corn or wheat residues and subsequently hitting flowering wheat heads. That means an effective way to avoid Scab is to have wheat flower when weather conditions do not favor the disease. One way to increase the chances of missing these weather conditions is to plant several wheat varieties with different “heading dates”. That will ensure that head emergence and flowering will be staggered through the spring, reducing the chance that environmental conditions will be conducive to Scab in all wheat fields. A second way to force wheat to flower over a period of dates in the spring is to stagger planting dates.

At Harvest: Scab infested grain heads have a pinkish hue. If scab is present the combine may be adjusted so that the light-weight diseased grain is removed along with the chaff. This will not remove all the infected grain, but can help reduce DON levels in grain heading to market.

Build A Plan Of Attack
Step 1: Purchase high quality seed with a standard fungicidal seed treatment like (Dividend Extreme, Raxil-Thiram, or RaxilXT).
Step 2: Review the list of wheat varieties (www.smallgrains.ncsu.edu/Varieties/VarietyCharacter.pdf) and pick at least three for production. They should include varieties with moderate Scab resistance and be from at least two different heading date classes.
Step 3: Stagger planting dates for the chosen varieties across several weeks.
Step 4: Plant conventional-till. If planting no-till avoid following corn or planting into wheat residues. If no-till production following corn is unavoidable, then shred, chop, or grind corn stalks as early as possible.
Step 5: Scout the field before harvest. If Scab is present, adjust the combine to remove as many of the diseased kernels as possible.

Need More Information?
Managing vomitoxins in feed grains.

Written By
Randy Weisz - Small Grains Extension Specialist, and

Paul Murphy - Small Grains Breeder