Wheat Leaf Rust and Stripe Rust An Emerging Problem Statewide in Texas

(April 16, 2024) - While recent rains have been a boon to many crops in the state, they have also presented an unfortunate emerging issue with wheat rust development throughout the state, according to Texas A&M AgriLife Extension Service specialists.

After years of drought, the moisture from recent rains coupled with warm winter temperatures has created conditions for the widespread development of stripe rust.

“Stripe rust is extensive this year, and we’ve been seeing it in our wheat trial plots and in producers’ fields for the past few weeks,” said Brandon Gerrish, Ph.D., AgriLife Extension statewide small grains specialist in the Department of Soil and Crop Sciences, Bryan-College Station. “Leaf rust came on a little later but has not been as widespread as the stripe rust.”

Gerrish said he and others in the department located throughout the state are continuing to see the development of rusts in many wheat-producing areas and anticipate the rusts will continue to develop and spread if not treated.

“The recent rains have increased the chances of helping maintain good yield potential but have also brought the rust that can detract from higher wheat yields, so it’s a mixed blessing,” he said.

“The majority of growers with a decent wheat crop to protect already have or should be applying fungicide on susceptible wheat varieties.”

The Rolling Plains have had good moisture and continued rainfall, so that area has been one where the rust problems have been worse, especially with stripe rust, Gerrish said.

“Texas wheat growers are no strangers to rust issues, but it has been a few years since they have had to deal with it, and the extent of the rust we’re seeing this year is more than usual,” he said.

On the positive side, Gerrish said, because of good growing conditions and more wheat acres planted, overall production for this year is likely on pace to exceed that of previous years.

A statewide prevalence of stripe rust

Emi Kimura, Ph.D., AgriLife Extension agronomist and associate professor in the Department of Soil and Crop Sciences based in Vernon, has been monitoring wheat trial sites and producer fields in the northern Rolling Plains.

“There has been a lot more rust in this area than we’ve seen in the past several years,” Kimura said. “Many producers are actively spraying their fields to control its spread.”

Kimura, who visited both wheat trial sites and producers’ fields, said disease pressure remains high, but there has been no significant additional spreading of rust on the affected wheat.

“Depending on the wheat varieties, rust pressure differed widely,” she said. “Varieties resistant to rust had a lower rust score, while other varieties susceptible to rust had higher rust scores.”

Stripe rust also has been prevalent across the southern Rolling Plains and Central Texas, said Reagan Noland, Ph.D., AgriLife Extension agronomist and assistant professor with the department based in San Angelo.

“There has also been some leaf rust reported, but that has not been observed consistently or at levels that are especially concerning,” Noland said. “It looks like untreated fields are beginning to get rust on the flag leaf.”

A recent rust report summary by experts in the Department of Soil and Crop Sciences focused on the South Texas and Blacklands regions also recognized an increased prevalence of both leaf and stripe rust in those areas.

According to the report, both leaf rust and stripe rust were observed at trial locations in Castroville, where there was high disease pressure. Oat crown rust and stem rust were also observed at that location.

According to the report, while stripe rust was the most prominent disease at the McGregor trial site, leaf rust was expected to develop further as temperatures increase.

Stripe rust was also observed at trial sites in College Station but was not as prevalent as at the McGregor and Castroville sites. Powdery mildew was observed in all three locations but not at what was deemed a serious level.

AgriLife Extension experts will continue to monitor fungal, bacterial, and viral wheat and oat diseases at these sites.

Producer decision-making on wheat

The variety of wheat a producer plants depends greatly on what the producer plans to do with the crop but can also affect the amount of rust issues seen in their fields.

“Many producers will grow wheat for beef cattle gains or even as cool-season silage for dairy cows,” he said. “Others will grow wheat to sell on the market, but that is greatly influenced by the price of wheat, which is currently fairly low. Producers must decide what is in their best interest economically.”

He said for wheat ultimately intended for grain production, it is generally a good idea to plant a variety bred for greater rust resistance. Texas A&M AgriLife-bred wheats TAM 115, TAM 116 and TAM 205 are all known for their resistance to leaf, stripe and stem rusts.

“Stripe rust severity varies widely across varieties relative to genetic resistance and fungicide application,” Gerrish said. “Many growers have applied a fungicide to try and curtail the appearance or spread of rust, with the products used ranging from lower-cost treatments that stop the existing rust from progressing to more expensive treatments that also provide some residual protection from further occurrences. The type of treatment also depends on the crop potential, growth stage, degree of rust infection and other factors.”

More information on wheat varieties can be found in the Texas Small Grains Variety Testing publication.

For more information, see the summaries compiled by AgriLife Extension district reporters.

Written by Paul Schattenberg