Wheat Disease Update – July 3, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Scab
There have been reports of wheat being rejected at the elevator for excessive vomitoxin (DON) levels in the grain due to head scab infection. The following was written by Dr. Arv Gybauskas from the Univ. of Maryland about blending good grain with contaminated grain. “The question arises can you blend the infected seed lots with clean seed to avoid a complete loss of the harvested seed. Blending to dilute DON levels is very tricky. In the EU it is even illegal once the grain has left the farm and is tested by an elevator or mill. The problem is DON is not uniformly distributed in the seed and without testing and complete mixing of truck-loads of seed you could still end up with a load that could be rejected. In that case you would even have lost the good seed. A better solution, although not an easy one nor is it a guarantee to make the seed marketable, is to further clean out the seed and have it tested again.

To avoid getting into this jam next time, it will take a complete management program that includes rotation, selection of varieties that have some resistance and only recommended fungicides applied when needed. We will present data and more details on these choices as we finalize the results from research trials this season.”

Grain Testing for Vomitoxin (DON)
The Delaware Department of Agriculture is conducting testing for DON in grower submitted samples. Growers should submit a 2 lb sample in a plastic zip-lock bag to the DDA in Dover (2320 S. Dupont Highway, Dover DE 19901). The sample should be clearly labeled with your name, billing address and telephone number. The costs are:

Vomitoxin test = $40/sample (DDA will provide a certificate that certifies the testing procedure). If the grower or their insurance company requires a USDA/FIGIS grade certificate, they will need to locate a laboratory that has that certification.

Grain grade factors (e.g. moisture, test weight, damage) = $15/sample

The link below describes the exact ELISA test that DDA will be conducting: http://www.neogen.com/FoodSafety/pdf/ProdInfo/Page_24.pdf.

Any questions please call the DDA Seed Lab at (302) 698-4590.

How to Get a Good Representative Sample for Testing
The reliability of testing is greatly influenced by the sampling procedure. To achieve a more accurate DON level estimate, it is critical that the collected grain sample be representative of an entire truckload or bin of grain. Grain and other particles separate based on particle size and density as it flows into a truck or bin. Typically, the smaller, denser material is near the center and the larger, lighter material is near the outside of the container. Therefore, it is expected that there will be a variation in the concentration of affected kernels in various portions of a truckload. In addition, since DON levels can vary greatly between kernels of similar size and density, it is important to take several samples from various locations within the load. Probe samples should not be taken from the center or outer portions of a load because these areas do not reflect a cross section of the load. The samples also must represent spatially distinct areas of the load. The probe should collect the sample from as much of the entire depth of the truck as possible. Four to five probes per truck are recommended. To obtain an accurate sample from an end gate grain stream, samples from the entire width and depth of the grain stream should be collected, not just the first and last portion of the load. A Pelican sampler or other sampling device aids in proper sample collection. At least four samples of the entire grain stream should be collected at intervals to represent spatially different portions of the load. Information from NDSU fact sheet “DON (Vomitoxin) in Wheat: Questions and Answers” http://www.ag.ndsu.edu/pubs/plantsci/pests/pp1302.pdf.

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