Just as the Kansas winter wheat crop is nearing its home stretch of development, it has hit a snag in the form of stripe rust and unusually cold weather, according to two Kansas State University scientists.

"We still have a lot of good-looking wheat out there, but stripe rust, particularly, has been found in wheat around the state," said K- State Research and Extension plant pathologist Jim Stack. "It really seems to be exploding in southern and western Kansas - it kind of kicked into high gear in the last one-and-a-half to two weeks."

The disease has been found at low severity in many areas around the state, but not in every field, he said.

"The weather conditions that favor wheat development - cool spring days with intermittent rain - also favor the development of such problems as stripe rust and powdery mildew," said K-State Research and Extension wheat specialist Jim Shroyer.

Stripe rust outbreaks occurred as recently as 2001 and 2003, but the difference this year is that about half the wheat planted in those years was resistant to stripe rust, Stack said. Much of that wheat was Jagger, which has been a stripe rust-resistant variety. The races of stripe rust this year, however, appear to be different than during those outbreaks, so Jagger's and other varieties' ability to fend of this race of stripe and other rusts is not fully known.

"We have found stripe rust developing in some fields of Jagger," he said. "Growers should not assume that fields of Jagger will not get stripe rust; they must scout these fields and monitor for stripe and leaf rust."

Symptoms of stripe rust are long, rectangular stripes of small yellowish-orange pustules on the leaves. These pustules consist of masses of rust spores. Leaf rust pustules occur in a random pattern over the leaf and are usually darker (cinnamon) in color. Stripe rust also goes by the name of yellow rust.

If left unchecked, stripe rust can kill the leaves of a wheat plant, so that it has no energy to form kernels, Stack said.

"The emphasis is on protection here. There is a sense of urgency about this because we're at a critical stage of development for wheat," he said. "The flowering to soft dough stage is where the biggest impact to yields occurs. But we can legally only apply fungicides up to flowering and we're already at or near that stage in parts of southern Kansas."

Stack recommended:

If growers see no symptoms of stripe rust, they should monitor their wheat closely every two days to check for symptoms.

If growers find stripe rust on lower leaves, they should evaluate their crop's susceptibility, which is determined by the variety of wheat, the near-term weather forecasts and the stage of development.

If growers find stripe rust on the upper two leaves, they should apply a fungicide.

If growers find that 50 percent of the flag leaf on the plants is destroyed, they should save the money and not spray.

Producers should check with their county or district Extension offices to determine what products to use if they decide to spray, the plant pathologist said.

Other diseases have also popped up around the state, but right now stripe rust is the biggest threat, he said. Leaf rust is also present in some fields, but it favors warmer weather.

"We need hot and dry weather to stop the rusts, but that's not in the forecast," Stack said.

In fact, temperatures dropped below freezing several times in late April and early May.

"Wheat is particularly vulnerable to damage from freezing weather from the late boot stage, as the head starts to emerge, through the flowering stage," Shroyer said. "Wheat starts to flower about five to seven days after heading. A freeze at that point can kill the
(flower) anthers outright or damage them. It can cause sterility if it happens at the right point in the wheat's development."

Anthers produce the pollen that is essential to kernel development.

In its April 25 weekly report, the Kansas Agricultural Statistics Service said that 89 percent of Kansas wheat was jointed. The crop's condition was rated 25 percent fair to poor, 57 percent good and 18 percent excellent. Disease reports indicated 71 percent with no presence of disease, 22 percent with light presence, 6 percent with moderate presence and 1 percent with severe presence.

KASS was expected to release an updated weekly report May 2.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus in Manhattan.