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Leaf rust fades but: Stripe rust hammers Arkansas wheat

Already lagging in acreage, much of Arkansas' wheat crop will probably lag in yield too.

“Stripe rust is kicking our wheat around,” said Gene Milus, a University of Arkansas plant pathologist. “For anyone who didn't spray a fungicide, stripe rust will likely put a dent in their test-weight yield. I see a lot of fields that should have been sprayed. You can walk into these fields with blue jeans and come out of them with orange or yellow jeans.”

In the southwest part of the state, many varieties are “nearly 100 percent covered with stripe rust. The wheat there has already flowered and is in grain-fill currently.”

Any producer who planted a susceptible variety has seen stripe rust hit his crop, said Jason Kelley, Arkansas Extension wheat specialist.

“I certainly hope most of those varieties have been sprayed. If not, they probably should have been. Visually, there are obvious, vivid differences between the susceptible varieties and non-susceptibles.”

Some late-maturing varieties and late-planted wheat still haven't fully headed out and remain within the fungicide-applying window, said Kelley.

Southwest Arkansas, where stripe rust was found earliest, has been hit most severely. Reportedly, 50 to 60 percent of “good fields” in the region were sprayed.

Stripe rust started earlier than normal last fall and conditions have remained favorable for it. “There are going to be some disappointed producers,” said Milus, who in mid-April toured wheat field around the state. “When a field is 90 percent stripe rust just after flowering, that isn't a positive sign.”

Kelley said because of a wet fall and inability to plant, the state has only between 150,000 acres and 200,000 acres of wheat.

“It's kind of hard to find a wheat field in parts of the state,” said Milus. “Wheat is scattered around. I just checked some fields around Marianna — in the row-crop land in the east. Stripe rust there has overwintered in hot spots. It's just beginning to show up in areas outside the hot spots. The wheat there is generally at boot stage, so it's still eligible for a spraying.”

If stripe rust overwinters in a field, “there's a lot of innoculum produced there — the hot spots — early in the season,” said Milus. “Then, it'll blow to other wheat fields from the centralized spots. I'm seeing a lot of that playing out this year.”


“The spores likely came in last fall and infected the wheat. You won't see any noticeable symptoms before February or March — maybe even April.”

Thus far, the weather has been a friend to stripe rust: cool temperatures, rainfall every few days, lots of moisture for dew formation and wind to carry spores. Kelley said the state will see stripe rust on the rise until nighttime temperatures hit the 60s. Once those temperatures are reached, the rust should slow down.

One positive, according to Milus: there's no indication producers are facing new races of the stripe rust fungus. “We're dealing with the same ones we're already familiar with.”

A few weeks ago, there were fears that leaf rust would also become problematic. It had already begun moving through the crop. Now, though, leaf rust has faded.

“I can't figure that out,” said Milus. “There was a lot more leaf rust around in March. Seeing that much so early disturbed me. But it's hard to find leaf rust in the southwest portion of the state now.”

Kelley too said the leaf rust disappearance “is perplexing. It was around even in late fall/early winter. A problem with it never materialized, though. That's kind of strange.”

In his tour, Milus also observed that “barley yellow dwarf is out there but not a serious concern. Septoria leaf blotch is at trace levels. We're also seeing powdery mildew on certain varieties — but it isn't major trouble, at this point.”


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