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Asian soybean rust not likely in Midwest this year, experts say

Agriculture.com Staff 08/13/2008 @ 2:49pm

Not much movement of Asian soybean rust has been noted in the southeastern U.S. in the last few weeks, and though this is an encouraging sign that there's no chance spores will descend upon Midwestern bean fields in time to do any damage, there are factors that have crop-watchers south of the Corn Belt a little more concerned.

Rust spores were found late last month in rainfall samples collected in Ontario and Manitoba, Canada. But, scouting has yet to turn up any rust in area soybean fields. Also to this point, rust has been reported in Florida, Georgia, Alabama, Louisiana and Texas, though it's been restricted to these typically rust-positive areas, with the northernmost sample coming in east Texas, according to Iowa State University plant pathologist Daren Mueller.

So, rust is out there. It may be similar to previous years' rust presence, but it's out there. Coupled with this year's relatively late soybean-planting in much of the Midwest because of poor spring and early-summer weather, is this reason to worry that this year's crop will fall victim to the fungus in levels high enough to cause economic loss?

Midwest agronomists say there's likely no reason to worry. Further south, however, field scouts know rust could sneak up on late-planted beans while they're still susceptible to damage, so they're keeping a sharp eye out.

"Last year, the weather was such that rust invaded the area early, in mid-September, which was unusual. In the past it has only developed in middle to late October," says Allen Wrather, University of Missouri (MU) plant pathologist at the MU Delta Research Center in Portageville, Missouri, in the Bootheel of the far southeastern part of the state. "Our worry is that the same will happen this year, and because of late planting, rust developing in mid-September could really damage yields."

But, Mother Nature has helped out. Weather conditions in rust-prone regions have actually taken a turn for the better in terms of rust propagation, Mueller says.

"Since [April], the weather turned dry throughout the southern half of Texas, and soybean rust has not moved out of [a] kudzu patch [in southeast Texas]," Mueller says. "In fact, drier than normal conditions continue to plague much of the southeastern U.S., which has slowed the movement of soybean rust, much like 2005 and 2006."

This means that even the latest-planted beans are likely not suspect to rust infection this year. According to data collected by ISU plant pathologist Palle Pedersen, even those midwestern fields planted the latest will have reached the R6 growth stage by mid-September, meaning even if rust does appear there, it will be too late to inflict economic damage before the fall's first killing frost. In fact, even if rust spores were to touch down in the Corn Belt right now, damage woul

"Even if we were to find soybean rust this week, it would not be at the level that requires immediate treatment," says Purdue University Extension soybean rust specialist Kiersten Wise. "In comparison to Brazil, our initial soybean rust spores are extremely low, which gives us extra time to apply fungicides, if they are needed at all."

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