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Corn+Soybean Digest

Rust still not as widespread as anticipated

Despite the confirmation of rust in Alabama, Florida, and Georgia, the incidence of the disease at this stage of the growing season is still not as widespread as was anticipated.

The most recent confirmed cases come on the heels of the finding of three rust spores resembling P. pachyrhizi, the causal agent of Asian soybean rust, in a spore trap near St. Joseph, LA., last week, as well as unfounded fears that tropical storm Arlene carried Asian soy rust spores from the southern U.S. into the Midwest in early June.

While each of these incidents has heightened the need for further scouting, no Asian rust has been found in fields other than the three reported cases. Because of the minimal occurrence of the spores in southern states at this point, many soybean specialists believe spread of the disease to northern states could be less widespread than expected.

Presently, there's no indication rust has spread to Alabama's neighboring states Mississippi and Georgia. On Thursday afternoon June 30, Phil Jost, Georgia Extension soybean specialist, said "We haven't found anything to worry about."

However, conditions in Georgia have been conducive to soybean rust over the last week of June. "If you wanted ideal conditions for rust to take off, Georgia has had them lately," said Jost. "We've been very rainy and humid, especially on the eastern side of the state. Thankfully, so far, no rust is showing up."

With drier conditions in Mississippi, Alan Blaine, state Extension soybean specialist, said he does not think they have Asian rust in his state. He says, "You have to consider where the rust was found in Alabama. They found it north of Gulf Shores on the coast -- it rains there frequently. I can assure you we haven't had rain frequently in the soybean-growing areas of Mississippi. Based on that, I'm not going to change my [spray] plans for our test fields yet. Even if it is spreading, it doesn't appear there's a whole lot of innoculum out there."

Currently, an Extension crew is in south Mississippi looking for rust, but as of June 30, Blaine says, "We haven't found anything suspicious."

He adds that most of Mississippi's soybean crop is at a stage where "we normally spray a fungicide for things other than Asian soybean rust. The decision for producers is whether to spray a (triazole/strobilurin) as well. But, at this point, I don't think we have (Asian rust)."

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