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For second time in three years: Stripe rust infests Southwest wheat

For the second time in three years a rare disease has hit wheat in the northeast corner of Texas and into several southern Oklahoma counties.

But farmers, Extension specialists and crop protection technicians were better prepared for the stripe rust epidemic this time around and most wheat, even susceptible varieties, seems to have escaped with minimal damage.

“The first time we got hit with stripe rust was in 2000,” says Jim Swart, Extension specialist at the Texas A&M-Commerce campus.”

Swart says the 2000 infection showed that some varieties are more susceptible than others.

“We've had some stripe rust for the last two years,” says Fannin County farmer Ronnie Lumpkins. “Cool, wet weather and foggy mornings seems to favor the disease.”

He says a combination of dry, warm weather in late April and application of Tilt fungicide seemed to stop the rust.

Lumpkins says in years past fungicide application provided “mixed results. But this year we got good control. I think may be our timing was better this year, and we used a full rate.”

He's also planting much of his acreage in a resistant variety, Pioneer 25R57. He would have planted more if seed had been available. “I planted about half my acreage in Pioneer 2571, a bearded wheat that has shown pretty good tolerance to other rusts. But I've seen stripe on it. I haven't seen any rust on the R57.”

Lumpkins says the 2571 variety has been a mainstay in his operation for years. “It's always been a good yielding variety.”

The second round of stripe rust in three years, however, may convince more growers that reliance on a single variety is too big a risk to take.

Swart says 2571 seems to be one of the most susceptible varieties. He and agronomist Don Reid say the disease occurs rarely in the area and usually with the following conditions:

Early planted wheat - We have seen more rust in the earliest planted wheat. We suspect that the younger wheat may have more tolerance to the disease. Most of the diseased plants are in boot stage or heading.

Greyland wheat (Wilson silt loam and Crockett loam soils) has more rust than wheat planted on Blackland. The greyland wheat has grown off faster and is in a more advanced growth stage (see note #1).

Susceptible varieties include Pioneer 2571, Pioneer 25R75, and Coker 9134. Coker 9663 shows some infection but appears to have more resistance than the other varieties.

The stripe rust epidemic was likely triggered by the cooler, rainy weather in mid-April.

Control options include fungicides and resistant or tolerant varieties.

“Tilt is the fungicide of choice to control this disease and it must be applied before flag leaf infection to get the most benefit,” Swart says.

Pioneer 25R57 appears to be resistant to this race of stripe rust. “Agripro Mason, Agripro Shiloh, and Agripro Bradley also show good tolerance.”

Swart says they may be dealing with a different beast this time, possibly “a different race of stripe rust than we experienced in 2000 as some of the varieties are reacting differently. For example, Pioneer 2571 was more tolerant to stripe rust in 2000 than it is now.”

Bruce Ward, with Helena, says up to 90 percent of susceptible varieties in the northeast corner of Texas needed a fungicide application for stripe rust. About 80 percent of susceptible acreage was treated on time, he says.

“Once a fungicide goes out, it's doing its work within 48 hours,” Ward says.

“This is only the second time we've seen this disease in this area since in the 1950s. Two years ago, we didn't spray a lot of the infected wheat and what we did spray was not on time, so we had yield losses. Since then, we've identified a number of varieties with resistance or near-resistance and have learned the value of timely fungicide application.”

He says a corner of one farmer's field was too close to residential areas to spray. “That section looked like the wheat had been defoliated,” he says. “The rest of the field was clean.”

Farmers still have questions about applying a fungicide to wheat at current prices. “It takes a five bushel yield increase to justify the expense,” Ward says. Timing also raises questions. “Often, by the time we see stripe rust on the flag leaf, it's already down in the plant. We also have questions about dry, warm temperatures that may stop the diseases in its tracks. It's a more difficult disease to manage than other rusts and powdery mildews.”

Ward also cautions farmers about saving seed for four or five years running.

Even with the stripe rust, Lumpkins expects a decent yield. “It looks as good as wheat has in several years,” he says.

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