Stripe rust on wheat.
Stripe rust on wheat.

Stripe rust, the most important disease for wheat growers in Arkansas, has been found in fields in Jefferson, Lincoln and Lee counties.

Terry Spurlock, an Extension plant pathologist for the University of Arkansas System Division of Agriculture based in Monticello, said the disease is appearing early in the season, similar to circumstances during the 2012 and 2013 growing seasons.

Spurlock said that although several “hot spots” of affected plants, found in clusters measuring from one to three meters in diameter, have been identified, cool winter temperatures are preventing the fungus from having much effect on the young crops.

“A lot of [the fungus] is on lower leaves,” Spurlock said. “It’s probably not doing much, as cold as it’s been. It’s just hanging out. Some of it was probably infection from the fall after the wheat emerged, although perhaps a few of these plants were infected recently.”

In affected plants, yellow or orange fungal pustules can be seen on leaves. Spores can be spread on the wind, or on humans or animals moving through the crop. If water is present on the leaf surfaces, the spores can germinate and infect the plant, Spurlock said.

Wheat is typically one of the top five crops planted in Arkansas, according to the U.S. Department of Agriculture’s National Agricultural Statistical Service. In the fall of 2014, approximately 390,000 acres of wheat were planted in the state.

Many wheat varieties in Arkansas are resistant to the fungus once they reach the adult stage, Spurlock said. However, if a plant is infected in an earlier phase, growers can suffer yield losses.

Avoid preemptive spraying

Spurlock cautioned growers against preemptively spraying fungicide, even if they find stripe rust on young plants in a field.

“Unfortunately, we deal with a lot of resistance issues with fungi, and especially fungi that reproduce as rapidly as some of these foliar pathogens,” Spurlock said. “The more applications of the same type of fungicides, the higher the risk is of developing a resistant population. Every time you spray a fungicide, you’re selecting against all the susceptible fungi that are out there, and selecting for everything that’s already resistant in that population, and it may not be the predominant population, or the predominant part of the population. But if you destroy all of it’s competition, it sort of has the run of the place, and it can become the dominant population.”

Spurlock said that growers’ best bet was to actively scout their fields as the season progresses and apply fungicides only where stripe rust appears to be taking hold, as opposed to tank-mixing the fungicide with other pesticides and spraying the entire crop.

“The problem with plant disease is, it’s never just one thing,” Spurlock said. “You kind of have to continuously scout. And just because you have stripe rust, it doesn’t mean it’s the only disease you’re going to have to deal with throughout a season. You have to approach it holistically, rather than just dealing with stripe rust. And I think that’s how most of our growers think about it.”