New cases of Asian soybean rust found in Alabama

Asian soybean rust continues to show up in Alabama fields at low severity. Since Sept. 9, there have been two new rust findings in the state.

“One was in a Clarke County sentinel plot near Jackson, about an hour north of Mobile,” said Ed Sikora, Alabama Extension plant pathologist on Sept. 14. “The plot was drying down and I found a few infected leaves low in the plant. It wasn’t anything major.”

The second discovery was in a small commercial field in Geneva County by Slocumb. It too had rust at low incidence/low severity.

It takes about two weeks after spore deposits for rust symptoms to show up. Knowing that timeline, Sikora has been keen to check north Alabama for any rust transported by Hurricane Katrina.

“(On Sept. 13), I drove into the north and northeast part of the state. I checked three sentinel plots and a handful of commercial fields but found no signs of rust.”

That doesn’t mean Katrina didn’t push rust spores north, cautioned Sikora. “It’s sketchy trying to find rust in a commercial field in early stages. I’ve been pretty lucky in finding it early in some fields. I thought I might find it up there, but no.”

Most of the fields in north Alabama are “yellowing up” into R-7. Many fields are being harvested.

“It’s also been hot and dry since Katrina passed through so conditions haven’t been favorable for rapid disease development.” Is Sikora seeing any defoliation due to soybean rust?

“The most interesting case we’ve had is one of the first commercial fields we found infected in Baldwin County. The grower has 50 or 60 acres he treated with Stratego about 21 days apart. He put the first fungicide on before knowing the disease was in his crop.”

Sikora visited that field earlier this month. There was very little defoliation.

“What’s interesting is across the road from the main field, the producer has a one-acre soybean patch — a different variety in the same maturity group.”

The farmer was unable to spray the patch with a fungicide. “He was aerial spraying and the patch is surrounded by power lines and trees. He left the patch as a check.”

As a result, the patch was hit hard by rust.

“Last week, it was thoroughly defoliated. That acre is a complete loss, I imagine. But right across the street, where he sprayed twice, the crop was protected from rust. That illustrates the power of a fungicide.”

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