The Impact Of DON

Before 1993, wheat growers hadn’t paid much attention to such terms as vomitoxin. But that year marked the first time producers, grain elevators, and millers noticeably felt the blow of the devastating mycotoxin deoxynivalenol (DON), with widespread incidence in eastern North Dakota and western Minnesota. Since then, the industry has taken notice of these more commonly used names for deoxynivalenol that has hit nearly every U.S. wheat-growing region.

Marcia McMullen, Extension plant pathologist at North Dakota State Uni­ver­sity (NDSU), has been studying diseases in cereal species for more than 25 years. She and other land-grant university plant pathologists have experienced the across-the-board impact vomitoxin has on the wheat industry with three different DON epidemics — in soft red winter wheat in 2003-04, hard red spring wheat in 2005, and hard red winter wheat in 2006-07.

The U.S. wheat industry needs high quality for both domestic and export markets. When a DON epidemic hits, growers’ crops become unmarketable or deeply devalued. Elevators face more difficulty marketing their supply. The profit margins of elevators and millers diminish as they test more loads, apply various technologies to sort out infected kernels, and reach out of their traditional buying radiuses to accommodate their customers by remaining below maximum DON tolerances.

Deoxynivalenol is a toxic substance produced by the fungus that causes a disease in wheat and barley known as Fusarium head blight, or “scab.” Because DON could pose a health risk to humans if consumed in high amounts, the Food and Drug Adminstration (FDA) has set guidelines for maximum DON levels allowed in finished wheat products. Any flour, bran, germ, or other wheat product entering the food industry should not exceed a DON concentration of 1 part per million (ppm). FDA has also set various advisory levels for wheat used in livestock feed. Because various technologies and processes are available to reduce DON levels in the finished wheat product vs. the raw grain, millers can set their own inbound ppm requirements — as long as the product they sell satisfies FDA guidelines.

As vice president of grain supply for Siemer Milling in Teutopolis, IL, Carl Schwinke takes on wheat quality as a priority. He explains that the milling industry’s standard for acceptable DON levels in raw grain is 2 ppm. In general, a grain supply with 2 ppm DON can become a wheat product (such as flour) with 1 ppm DON through the mill’s cleaning and blending processes. Depending on the crop’s end-use, though, different grain elevators or millers may make standards more stringent. Grain for a whole wheat end-use has a 1 ppm industry-set standard at delivery, and grain for a bran end-use usually has the criterion of 0.5 ppm at delivery.

Schwinke says that his company may accept grain with DON measures greater than 2 ppm, but only if the company believes that it can achieve the 1 ppm advisory level with the total grain supply it purchases. The grain seller will receive discounts, though, based on the DON measurement and other quality factors like test weight and amount of kernel damage.

“We process all the wheat we purchase into flour for human consumption — cookies, pastries, pancakes, all kinds of batters,” says Schwinke. “Our interest is providing that food-grade product. Frankly, we eat, too. We want the safest food products reaching the end-user, so we want those DON levels to be as low as possible.”

The Cost Of DON

“DON affects everyone in the wheat value chain,” says Schwinke. “In effect, scab stops kernel development and growth. So if scab infects the plant in earlier stages of grain development, the kernel may be smaller, shrunken, or have lighter test weight than quality wheat. The disease stops any intake of nutrients, too.”

Schwinke says that this loss is felt across the wheat industry. Producers’ yields decrease, and they see more discounts for quality and grain damage. Marketing grain becomes a bit more of a struggle for grain elevators as they try to sell what the market can absorb. Elevators might need to bin grain separately according to different levels of DON stored in their facilities. Milling yields fall, as well as millers’ profit margins. And the end-user faces a higher cost for flour.

“From the miller’s perspective, we face the problem in epidemic years of paying for higher-priced grain that originates from our normal supply territory and additional cleaning of grain that we receive from our regular suppliers,” adds Schwinke. “We conduct more testing, which requires special equipment and personnel training. Maintaining state-of-the-art wheat cleaning equipment is a large expense. DON adds a tremendous amount to our operational costs.”

Screening, airflow, and gravity tables help separate the smaller, under-developed scabby kernels from the rest of the grain, but at an expense and slow pace. Adding the cleaning step to the milling process or at the elevator, though, won’t eliminate DON from the grain supply. Late scab infections might show no visible damage but could still cause elevated DON levels.

Schwinke stresses that millers are responsible for supplying bakers and the food industry with flour that meets FDA standards, and there are no effective methods of sorting out these late-infected kernels. Thus, millers need to source wheat from other regions when DON is not properly managed in their normal buying regions.

Buying out-of-area grain adds additional transportation and freight costs to the operation. Railcar availability may be limited, potentially causing grain supply insufficiencies. Matching flour consistency becomes more difficult because the imported wheat may not have the same milling characteristics as the regional wheat normally used. All these extra expenses add to the discounts growers receive when they sell scabby wheat.

The Fight Back

Many local grain elevators, regional mills, and Extension specialists have played an integral role in educating wheat growers on DON and the fungus associated with the mycotoxin since the first scab outbreaks. They have stressed that a combination of technology and smart growing practices can reduce the potential for high DON levels and help protect wheat quality. NDSU’s McMullen suggests:

â–  Plan good crop rotation systems that plant wheat after broadleaf crops such as soybeans, canola, and flax.
â–  Avoid following corn and minimize wheat-on-wheat rotations.
â–  Choose wheat varieties with improved scab resistance.
â–  Assess the region’s scab risk using tools such as www.wheatscab.psu.edu or check to see if your own state has a risk outlook tool.
â–  Apply fungicides proactively to control and avoid diseases.

Randy Myers, Bayer Crop Science fungicide product manager, says a growing number of U.S. wheat and barley producers are relying on annual fungicide use as a proactive measure for overall crop protection.

“Annual, proactive approaches to disease management are the most effective because scab on cereals cannot be cured,” explains Myers. “If warm, humid climate conditions and moist soil are present as grain heading approaches — and the Fusarium pathogen is present — disease will develop. You don’t want to wait until you can see signs of the disease to spray, because then it’s too late to get the most out of your fungicide applications.”

Mark Huso is a retailer and crop advisor with Lake Region Grain in northeastern North Dakota. “When I discuss my crop protection strategy with my growers, I tell them that it’s just as efficient to use fungicides as it is to use herbicides,” says Huso. “I recommend fungicide use every year, and my customers see better yields and quality consistently.”

In 2008, Huso administered a strip field trial comparing the new Prosaro fungicide from Bayer CropScience with another fungicide. Although the season was virtually disease-free, the gains in yield, protein levels, and test weight gave the wheat treated with Prosaro an economic advantage over non-treatment and the other fungicide.

Across all kinds of conditions, Pro­saro has been proven to reduce mycotoxins by 50% to 60%. According to Bayer CropScience, no other fungicide reduces DON levels better on wheat and barley than Prosaro.

“In years of heavy scab pressure, this level of reduction could mean preserving the marketability of a crop,” says Myers. “In years of lighter pressure, it means producing an even better crop than expected and helping to secure premiums for high grades. With the industry’s best activity on scab while controlling a broad range of important foliar diseases, Prosaro is a hedge against quality discounts and yield losses and a weapon against scab and DON.”

The Bayer CropScience recommended application rates for Prosaro are 6.5 ounces per acre under normal conditions and 8.2 ounces per acre under high disease pressure. For optimal activity vs. scab in wheat, Prosaro should be applied at Feekes growth stage 10.51 (early flowering). The appropriate Feekes growth stage for scab suppression on barley is 10.5. In areas not threatened with scab infections, Prosaro may be applied at earlier growth stages for control of yield-limiting foliar diseases on wheat including leaf rust, stem rust, Septoria leaf blight and glume blotch, tan spot, and powdery mildew.

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