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Asian soybean rust in the Corn Belt? Not likely this year, specialists say

With recent reports of Asian soybean rust discoveries in northern Texas and Arkansas, the disease seems to have braced itself with a stronger foothold in the U.S. this year.

"As quickly as they have been declaring infected counties, you almost have to take note," writes Agriculture Online Marketing Talk discussion group poster MoInfo. "There are almost twice as many infected counties in the South as there were one year ago this date."

Even with rust discoveries further north than usual for this time of year -- into northern Texas and Arkansas -- the weather forecast combined with the soybean crop's development, which USDA-NASS pegged as slightly ahead of the average pace in Monday's crop progress report, likely will add up to very little chances of rust reaching the Corn Belt before harvest, especially now that we have passed the mid-July threshold at which rust spores must be introduced in order to cause soybean yield damage.

"You can find it down there, but you have to look very hard for it," says Ohio State University Extension agronomist and Successful Farming High Yield Team expert panel member Jim Beuerlein of the rust spores in the southeastern U.S. "And, it's not sporulating very much. For it to get up [to the Corn Belt], it's got to do a lot of growing down there, then have a storm to blow it up here."

Forecasters don't expect the latter part of the equation anytime soon. According to QT Weather meteorologist Allen Motew, current projections show low chances for storms and corresponding northerly wind currents despite eastern Corn Belt weather that would otherwise favor rust's spread.

"The low-level wind field is expected to be southerly, but not strong or sustained for the next 10 days," Motew says. "Easterly winds in Florida could be transporting spores into Georgia and Alabama. If viable spores of the Asian rust fungus were to reach Indiana, conditions appear to be favorable for infection. For the present, however, there does not appear to be enough rust in the southern Mississippi Valley to pose a risk for Indiana."

Regardless of how the weather plays out, Beuerlein says already low rust spore counts in the areas where infection has been confirmed, combined with the required timeframe for the rust spores to reach the Midwest in time to do any damage, make it next to impossible that infection could become serious further north between now and harvest.

"It's important to know that the spore count down there is very low and it's too dry to do anything. It has to have three to six weeks to build up down there, then something to get it up here, which can happen in 10 days or so," he says. "But then once it gets here, it needs six weeks to do anything. We could get some of the stuff up here very late in the season, but not early enough to do any damage."

But, the Ohio agronomist says even though the chances of rust robbing Corn Belt soybean yields are low, growers shouldn't lower their guard when it comes to scouting their fields, as other pests have been noted in damaging numbers around Ohio.

"Keep scouting, because you might find something else," Beuerlein says. "Aphid counts are also very low, but we do have major Japanese and bean leaf beetle populations, so we will have to spray for them."

With recent reports of Asian soybean rust discoveries in northern Texas and Arkansas, the disease seems to have braced itself with a stronger foothold in the U.S. this year.

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