No. 12 Article 11/June 12, 2009

Wheat as Harvest Approaches

After a good winter and early spring, wheat crop prospects have taken a considerable nosedive in Illinois due to frequent bouts of wet weather over the past 6 weeks. Carl Bradley has described the diseases that are prevalent in many southern Illinois fields. I have not yet seen the variety trials in southern Illinois, but reports are that diseases will take a serious toll on most of the wheat crop in the areas where most of the crop grows.

Heading ranged from normal to several days later than normal in Illinois wheat this year. As is usual for years with too much rain in May, diseases are causing accelerated maturity as leaves and heads start to die in southern Illinois. Harvest will begin soon, if it hasn't already.

With so much of the soft red winter wheat in areas with high levels of Fusarium head blight (FHB, or scab), the prospect of high vomitoxin (DON) levels in the harvested grain has wheat millers very concerned. In fields that experienced rainfall throughout much of the flowering period, FHB infection was early and severe, and most of the infected kernels will have failed to develop. These will typically be blown out of the combine and so will not contribute much to the DON level in the grain. When the infection spreads after flowering to kernels that remain in the harvested grain, they can have very high DON levels, which can lead to large dockage or even refusal of the grain at the elevator. One feature of DON is that it can be very high in a small proportion of the kernels, making the whole lot exceed the threshold for marketing for certain uses. Unfortunately, such kernels may have the same size and density as uninfected kernels, so it may be impossible to separate them out.

There's no way to reduce the amount of DON that will develop in infected kernels, but raising the amount of air used in grain separation during harvest can blow more light kernels out, so may reduce the overall level of DON. This of course leaves more grain in the field and reduces harvested yield. In a high-DON year, such yield loss can easily be compensated for by lower DON levels and higher price of the delivered grain. Another approach might be to have DON tested following harvest and then run the grain through a postharvest separation (perhaps using seed-cleaning equipment) to see if levels can be reduced enough to lower the dockage or to at least make the grain salable.

In central and northern Illinois locations there was less rainfall during flowering, so crop conditions look much better now. Our research trials at Urbana have very low levels of FHB and seem to be maintaining reasonably healthy leaves as grain-fill progresses. If DON levels are high in other areas of the soft wheat area, wheat with low levels might be a sought-after commodity this year.--Emerson Nafziger

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