Fusarium Head Blight (scab) is a fungal disease, which can cause significant yield loss in wheat. Research from the LSU AgCenter shows how proper timing of fungicides is key for treating scab.

Boyd Padgett, Extension and Research Row Crop Plant Pathologist for the LSU AgCenter and LSU College of Agriculture, discussed managing scab in wheat acres, during the recent online Louisiana Agricultural Technology & Management Conference.

Causes of scab

Fusarium Head Blight has been a significant problem for the Louisiana wheat crop for the last five to six years.

"When looking at the disease cycle, the infection can occur from head emergence to harvest," Padgett said. "However, it is most damaging when infection occurs at flowering. The fungus also produces a mycotoxin called DON, so your load can be rejected at the elevator like corn with aflatoxin."

The fungus likes temperatures between 60 and 90 degrees as well as leaf wetness periods of high relative humidity for about four to six hours.

"You can rotate to non-host such as soybean and cotton, or you can use moderately resistant varieties," he said. "You can also plow under your debris."

The disease is caused by two types of spores, which can be liberated during heading. Once it successfully infects the spikelet, infection results in bleached wheat heads.

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"Rarely do you see an entirely bleached head; instead, it is usually partial bleaching," Padgett said. "The fungus then produces two spores, and it starts all over again."

Fungicides for scab

A new fungicide, Miravis Ace, which is produced by Syngenta, looks promising.

"Dr. Price and I have done some work with Miravis Ace, and we have both seen some favorable results," Padgett said. "It is suppressive, and it contains two different active ingredients. One is Pydiflumetofen (Adepidyn) and the other is Propiconazole, a DMI sterol inhibitor.

"There are two other fungicides that can also be utilized, Prosaro and Caramba. In tests I conducted in 2018 at Dean Lee and Alexandria, all these treatments were applied at about 50% flowering, and Miravis Ace did a nice job as well as the other products when compared to the non-treated."

In 2020, Padgett and Price conducted timing studies for fungicides.

"Price did one at the Macon Ridge Research Station while I did one at the Dean Lee Station," he said. "We applied Caramba, Prosaro, and Miravis Ace on different plots at flowering, all single applications.

"We also had an application of Miravis Ace six days after flowering. The flowering applications looked pretty good, and the results were reflected in the yields. However, when we waited six days after flowering to make an application, we paid the price and saw a yield decrease relative to the other fungicide treatments."

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Applications applied at flowering performed best across all treatments used.

"There was a penalty as far as control relative to the heading stage, which was reflected in lower yields compared to the other fungicide timings," Padgett said. "If we waited six days after flowering, we had extreme pressure. It was no better than the non-treated plots, so keep that in mind if you must make fungicide applications this year for scab. Bottom line, an application at flowering is best for managing scab."