Alabama Wheat: Head Scab Could Leave You Holding The Bag

Wheat head scab. Photo: Josh Bailey

Fusarium Head Blight, also know as head scab, can be devastating when it occurs. The U.S. wheat industry loss over three
billion dollars due to head scab in the 1990s.

Losses from head scab include lower yields and test weight (along with low test weight, head scab damaged seed typically have low germination and produce unthrifty seedlings with a poor survival rate) but the most devastating losses come from the production the mycotoxin deoxynivalenol (DON) also known as vomitoxin.

The wheat, depending on the levels of DON, may be unsalable due to the dangers to humans and livestock.

Wheat is heading now in north Alabama and it will soon be time to apply a fungicide for head scab. The photo below shows the ideal time to apply a fungicide to reduce the incidence of head scab. The best fungicides for head scab control include Prosaro and Caramba.

These fungicides usually reduce the severity of head scab and the DONs associated with the disease by half if applied correctly.

Alabama Extension pathologist Austin Hagan advises, “While some wheat varieties are less susceptible than others to scab, fungicides are the main line of defense. A protective fungicide application for scab control should be made at early flowering for best results.

“Prosaro at 8.2 ounces per acre and Caramba at 17 ounces per acre generally provide the best scab protection, though no fungicide will give 100 scab control. Maravis ACE at 13.7 ounces per acre when applied at early flowering is also labeled for scab control on wheat.”

Propiconazole and Tebuconazole are also labeled for head scab suppression. Do not follow an application of a tebuconazole fungicide with an application of Prosaro as this treatment program will result in excessive tebuconazole residues in the grain.

Fungicides applied for head scab will provide protection against other foliar diseases. Please note that all the products labeled for head scab are triazole fungicides. Strobilurin fungicides applied when a scab application should be made have shown to increase DON levels in wheat by killing fungus competing against the DON mycotoxin.

Wheat drilled behind no-till corn is at the highest risk for a head scab outbreak if given favorable weather for the disease. Severe scab outbreaks are likely when three or more rain or irrigation events occur from the start of flowering (anthesis) through three to five days post-bloom, particularly on scab-susceptible varieties.

Extended post-flowering rains also contribute to increased disease severity and elevated mycotoxin contamination. Conversely, dry weather during this period will suppress scab development.

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