Managing Fusarium head blight on wheat
Fusarium head blight, commonly called scab, is caused by fungi in the genus Fusarium. It is the single most important disease of wheat and one of the most difficult to prevent. The disease can cause spikelets to appear bleached. Severely infected kernels tend to be shriveled, light weight and, sometimes, chalky white or pink in color. Fusarium head blight is capable of causing some loss in grain yield, but the most significant financial losses stem from a mycotoxin created by the fungus within the infected grain called deoxynivalenol (DON or vomitoxin). More information can be found at the Scab Smart Management Web site.
Phil WhartonSymptoms of Fusarium head blight include wheat heads that become partly or completely discolored. Weather has the greatest influence on disease development. Damp conditions and moderately warm temperatures at the time of flowering are most advantageous to the pathogen. However, it may also be favored by wet weather several days prior to flowering as it encourages spore numbers and dissemination. Likewise, wet conditions following flowering can compound the problem as it favors both disease development and the production of DON. Use the Fusarium Head Blight Risk Assessment Tool to access a risk model based on local weather, and sign-up to receive in-season scab alerts.
Varietal resistance offers limited protection from Fusarium head blight as the highest yielding varieties currently grown in Michigan are moderately to highly susceptible. However, breeders are beginning to release less susceptible varieties that could help reduce DON levels. Michigan State University’s annual variety trial results report a Fusarium head blight index for all varieties.
Wheat is considered to be flowering when one or more anthers are visible. Flowering generally follows heading by just a few days. Soft white and soft red wheat, as sub-classes, are generally comparable in their susceptibility to Fusarium head blight, though white wheat is often more apt to accumulate DON. Soft white wheat is also disadvantaged by being more likely than soft red wheat to incur discounts because of their different end-uses. While market discounts vary, soft white wheat growers may experience discounts beginning at 1 ppm of DON, whereas discounts for soft red grain may not be imposed until 2 or more ppm.
Crop rotations matter, as residues from the previously infected crop can harbor the Fusarium that causes Fusarium head blight. Residues that represent the greatest risk are those from corn, followed by wheat and barley. Hay sods can also pose a significant risk based on industry experience in Michigan. Using tillage to incorporate infected residues will reduce disease risk, but will not completely mitigate the threat that these rotations pose.
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