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Stripe rust leading wheat disease threat

In test fields at the LSU AgCenter in Winnsboro, La., Stephen Harrison shuffles between rows to evaluate more than 60 wheat varieties and over 400 breeding lines of plants.

First it was leaf rust, now it’s stripe rust that is worrying wheat farmers, and Harrison knows far too well how one destructive disease — over just one season — can trump another similar one.

“It’s cyclical, we see this happen about every four to 10 years,” Harrison, professor in the LSU department of agronomy, said.

Presently, scientists and Extension agents are encouraging wheat farmers to be careful and deliberate in the varieties they choose for the next planting season and to make multiple selections.

Harrison said it’s wise for farmers to plant three or four kinds of varieties and not count on profitable yields from simply one — a gamble with the looming threat of stripe rust.

“It’s important to not just look at one high-yield variety or rely on what your neighbor is saying has worked for him,” he said.

Instead, Harrison said farmers should pay close attention to data collected from the land grant system and discuss plans with local agents.

“Look at the good varieties and make sure you start with the best genetics possible,” he said.

Expensive fungicides

While various fungicides may control the spore disease if applied early, but input costs are expensive, thus compounding farmers’ economic decision-making. Boyd Padgett, LSU AgCenter plant pathologist, said fungicides that resist stripe rust cost $10 to $14 per acre and application costs are about $4 an acre (and continue to rise with fuel costs).

Consequently, farmers can manage rust disease with fungicides, but doing so may be more expensive than the initial cost of purchasing preferred varieties.

Padgett said wheat farmers are reticent to apply one fungicide spray, let alone apply multiple sprays.

Padgett’s peer, Clayton Hollier, said researchers are receiving inquiries from farmers about fungicide recommendations. But because stripe rust has unexpectedly emerged, testing has only recently gotten under way.

“Are we wasting money and time with early applications? We don’t know yet,” Hollier said. “We are going in (on test plots) as early as possible and making fungicide applications randomly to see how much yield loss there is.”

Additionally, he said, scientists are hoping to get input from economists measuring the test results.

Recent weather conditions in Louisiana are at least partly to blame for heightened stripe rust activity, according to Harrison.

“The weather pattern was unusual this winter. It was a warmer winter and a cooler spring and that forms stripe rust,” he said during a recent LSU AgCenter field day.

Bill Hutchinson, LSU ag director for the northeastern region of Louisiana, described the disease as “potentially devastating.”

“Up until last year, stripe rust was an occasional problem, now it looks like it is here to stay.”

Natural selection

The ability of disease organisms, such as wheat rust, to adapt and overcome resistant varieties developed collaboratively by university scientists and seed producers from the private sector is analogous to a never-ending game of chess. Scientists and breeders constantly try to stay one step ahead of diseases, but it’s not easy.

Hutchinson, who has studied wheat diseases in some capacity for about 26 years, said it’s a matter of numbers. As many varieties as scientists can breed in a certain pool, he said, it’s typical for no more than just a few to emerge and have substantial disease resistance.

Even successful varieties hold immunity for only a limited time — typically only one or two seasons at best.

“There is a lot of luck involved because we can’t control how these diseases mutate,” Hutchinson said. “It’s extremely important to select the right variety. Disease control and variety selection go hand-in-hand.

“You can change other inputs, but you have sealed your fate for the year in the seeds chosen.”

Because of a disease’s quick, natural adaptation, particular varieties on a recommended list for farmers last year may be scratched off entirely this year. “It’s amazing how much rust has changed over the past year,” Harrison said.


Despite rust’s competitive nature, Hutchinson noted research has made remarkable progress over the last two decades, progress that has benefited the environment, helped keep the cost of wheat down for consumers, and provided agronomic advantages.

Years ago, he said, varieties produced weaker stems that couldn’t support taller, larger wheat leafs. Now, research is devoted primarily, but not entirely, to yield improvements.

“There have been tremendous advances in traits, but the environment continues to change,” he said. “Next year the rules of the game will change again.”

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