This is a nice time of the year in the Mid-South. Temperatures are warming, the rains are starting to become less frequent and dark-green fields of grain are waving in the breeze in parts of the country where farmers still sow winter wheat.
Unfortunately, farmers in Louisiana and some parts of Arkansas have begun observing fields where the grain is not so green and, in fact, is beginning to show the telltale signs of bleaching that generally accompany infections by Fusarium head blight or scab.
“What you’ll see is the wheat looks to be maturing when it’s not supposed to be mature,” says Paul “Trey” Price, field crop pathologist with the Macon Ridge Research Station near Winnsboro, La. “You’ll see bleaching of the heads. This is not normal. That’s the result of infection by the pathogen that causes Fusarium.
“It also causes shriveled seed, and I’ve picked some out of the field here,” said Price, referring to a set of plots where scientists are screening wheat varieties for possible resistance to scab. “This is milk stage wheat. It looks like it is supposed to be maturing, but it’s not.”
Price was speaking at the Wheat and Oats Field Day held at the Macon Ridge Station on April 22. The field he was referring to had been inoculated with wheat scab through a sprinkler system, but a number of fields in central and northeast Louisiana are showing symptoms of the disease, as well.
“If you look at this field out here, you can see that the wheat is maturing,” said Dr. Price, pointing to an adjacent field at the Macon Ridge Station. “It’s not supposed to be maturing; that’s milk stage wheat. This is what’s it’s going to look like from the turn row, except hopefully not this severe.”
Dr. Price said outbreaks of wheat scab can be variable, having been reported in the Great Plains, central U.S., Mid-South and Southeast over the last 20 years. Losses have been reported as high as 20 percent in isolated fields with susceptible varieties.
“Some losses have been reported up to 80 percent, so it can get bad under the right conditions,” he said. “Those are wet, warm weather during flowering. The fungus may infect wheat from flowering up to harvest with the most devastating infections occurring during flowering.”
Price and Boyd Padgett, field crops pathologist and regional director at the Dean Lee Research Station in Alexandria, La., said they had received multiple reports of wheat scab or Fusarium head blight from producers and consultants during the last two weeks of April which corresponds to the flowering period for many fields in Louisiana.
Symptoms of the disease will first appear ten to 14 days after flowering as bleached heads. Upon closer inspection, affected wheat heads will usually have infected kernels showing the characteristic bleached appearance with pinkish/salmon/orangish coloration along the glumes.
“This coloration is millions of microscopic spores of the fungal pathogen. There are usually healthy kernels along with the diseased kernels on the same head,” says Padgett. “In extreme cases, however, the entire head may be infected. At harvest, affected seed will be shriveled, off color, and much lighter than healthy kernels and are referred to as ‘tombstones.’”
Plant breeders have two types of resistance they can try to use to fight scab. One is Type 1 resistance that prevents the plants from becoming infected with scab. Type 2 prevents the disease from moving up and down the plant once it becomes infected.
“Type 1 has proven to be elusive,” said Price. We’re hoping we can find some varieties in this test that will be more resistant to the disease in years when it is more prevalent such as 2015 and 2014.”
Fusarium graminearum, the pathogen that causes scab, is also responsible for ear, stalk and root rots in corn. “So it’s fairly ubiquitous in this area,” said Price. “That brings up cultural practices than can help – practices such as crop rotation, tillage, even mowing.
“Another thing that has been suggested is staggering planting so your entire crop won’t be flowering at the same time and thus not susceptible at the same time. Or maybe you will have the opportunity to plant varieties with different maturities to avoid flowering at the same time and miss the infection on the entire crop.
The researchers say triazole fungicides may be somewhat effective on FHB. “Some of the earlier research showed that tebuconazole (Folicur and generics) may reduce incidence and severity of Fusarium head blight,” Price said.
“Later research shows that Prosaro, Proline and Caramba may be efficacious on FHB. But it should be noted that under ideal condition and timing, the maximum control with these materials was around 50 percent.”
Timing is critical, says Price. Researchers recommend application of the fungicides with ground equipment for proper coverage. “But if it’s wet like it was for much of this season, you can’t get in with ground equipment and you miss the window.”
Angle the nozzles
For ground sprayers, nozzles angled at 30 degrees will help put more fungicide on the wheat head than if the nozzles are positioned to spray directly above the wheat. Some research has shown that dual nozzles angled in opposite directions will also increase head coverage.
The vast majority of fields in Louisiana are currently past the application window, the researchers note. “Fungicide applications at this point would likely by off label and ineffective.”
One step growers can take is to increase the fan speed on their combines when they begin to harvest wheat. “I’ve shown you these shriveled heads that have resulted from the disease,” said Price. “These seeds are much lighter than healthy seeds so you can adjust your fan speed and blow them out the back of the combine. That can remove a lot of those diseased heads and increase the overall test weight for your grain.”
To read more about Fusarium head blight in wheat, visit http://www.scabusa.org/