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ALERT: First Asian soybean rust in Oklahoma infects two SE counties
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By Marilyn Cummins, Editor
StopSoybeanRust.com
7/26/2007 10:30 p.m. CDT -- Asian soybean rust was confirmed for the first time in Oklahoma on a leaf sampled from a sentinel plot in Bryan County on July 13, making Oklahoma the eighth state with rust this year. Soybeans in Choctaw County were found to have rust two days ago.
The two counties are in southeastern Oklahoma, directly across the border from rust-positive Fannin County in Texas and only two counties west of rust-positive Little River County in Arkansas. This is the farthest north soybean rust has been found in the U.S. this year.
According to the Oklahoma state commentary that reported the finds today:
"Rust was found for the first time in Oklahoma on a sentinel plot sample taken on 13 July from Bryan Co. (south of Bennington) on one of 100 leaves sampled. By 23 July, rust increased to an incidence of about 20 percent of sampled leaves in the sentinel plot. On 23 July, rust was also found in a nearby commercial field at an incidence level of 10 percent.
"In adjacent Choctaw County, rust was found in a commercial field (near Frogville) at an incidence of 1 percent on 24 July. Rust has not been found in the sentinel plot, kudzu, and in other commercial fields in Choctaw County. Positive finds have been in soybeans at the R4 to R5 growth stages."
Sentinel plots in Atoka, Ottawa, Payne, Sequoyah, Tulsa, and Washington Counties remain negative for rust this week, the report said. Rust also has not been found in observational samples taken from commercial fields in Garvin, Pottawatomie and Le Flore Counties.
"While rains have subsided, conditions remain favorable for rust development this week with moderate daytime temperatures, high humidity and nightime dews," according to the commentary. "Other diseases, such as downy mildew, brown spot, bacterial blight, and frogeye leaf spot, are widespread and make rust recognition difficult."
Oklahoma officials said fungicide sprays are recommended to protect soybeans from rust in affected counties and nearby counties to the north when soybeans are in the R1 to R5 growth stages. The decision to spray at late R5 is a judgment call. Check soybeans periodically and submit suspect samples to local County Ag Educators for submission to the OSU Plant Disease and Insect Diagnostic Laboratory.
As of July 26, early maturing varieties (MG3 and MG4) are at R3 to R5 growth stages in Oklahoma, while full-season varieties (MG5 and MG6) are at various vegetative stages.
These finds bring the U.S. total of counties and parishes with soybean rust in 2007 to 45 in eight states: Texas 15, Florida 10, Louisiana 6, Alabama 5, Georgia 5, Oklahoma 2, Arkansas 1, Mississippi 1.
On this date last year, only 26 counties and parishes in five states had soybean rust, and it had gone no farther west than Rapides Parish, Louisiana, and no farther north than Montgomery County, Alabama.
Source: Oklahoma state commentary and historical data on www.sbrusa.net.
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