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Arkansas wheat dodges head scab disease

Rainy weather during April and May promoted a low level of Fusarium head blight, also called “scab”, across Arkansas wheat fields in 2008. The disease showed up as partially blighted heads during soft dough stage across most of the state, but yields were not affected.

The fungus that causes scab produces several toxins that can contaminate harvested grain, leading to concerns for food and feed safety. Deoxynivalenol (DON) is the most commonly produced toxin, and wheat grain with less than 2 ppm DON is considered acceptable for making flour than must contain no more than 1 ppm. DON usually is associated with shriveled, lightweight “scabby” kernels that tend to be removed from healthy kernels during harvest and subsequent cleaning at the flour mill.

To assess the levels of scab and DON in the 2008 wheat crop, Cooperative Extension county agents with the University of Arkansas Division of Agriculture in 15 counties collected 120 random grain samples from commercial fields and submitted them for analysis. Samples were visually rated for the percentage of scabby grain by comparing each sample to a set of known standards and were analyzed for DON content by a testing laboratory at the University of Minnesota.

Only three samples had more than a trace of scabby grain, 19 percent had a trace of scabby grain, and 78 percent of the samples had no detectable scabby grain. Results of toxin analysis determined that 31 percent of the samples had no detectable DON, 54 percent had levels below 0.3 ppm, 14 percent had levels between 0.3 and 1.0 ppm, and only one sample had a level greater than 2 ppm.

These results indicate that grain from the 2008 Arkansas wheat crop was safe and wholesome. The grain survey and DON analyses were funded in part by grants from the US Wheat and Barley Scab Initiative, which receives its funds through the US Department of Agriculture.

The US Wheat and Barley Scab Initiative also funds research to develop and implement integrated management strategies for controlling scab and reducing the level of DON in wheat and barley. Resistant varieties are in various stages of development, but no highly resistant varieties are currently available for Arkansas. Several fungicides were found to be moderately effective for reducing scab and DON if applied at flowering time. Fungicides such as Folicur, Proline, Prosaro, and Caramba have been registered recently on wheat, primarily to control scab, but also for foliar fungal diseases such as rusts, leaf blotch, glume blotch, powdery mildew and tan spot. A scab forecasting system has been developed to predict when fungicide applications are most likely to be needed. See the US Wheat and Barley Scab Initiative Web site for more information on scab and its management.

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