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ALERT: Soybean rust confirmed in north-central OK, in AR and FL counties
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By Marilyn Cummins, Editor
StopSoybeanRust.com
8/6/2007 10:30 p.m. CDT -- Asian soybean rust has jumped to the north-central Oklahoma county of Payne and was reported in one other Oklahoma county, two new Arkansas counties and one new Florida county today.
The soybean rust in Payne County (county seat: Stillwater) -- found on one leaf out of 100 sampled from a soybean sentinel plot -- is the farthest north rust has been confirmed in 2007. It's just two counties from the Kansas line, below Sumner and Cowley counties, KS. The other new rust was found at 10-percent incidence in the sentinel plot for the southeast Oklahoma county of Atoka, adjacent to the two other positive counties in the state on its southern border.
With these finds, and those announced for Lafayette and Miller counties in southwest Arkansas and Escambia County in the Florida Panhandle, the total count of U.S. counties and parishes hit 61 today, in eight states. As of Aug. 6 last year, only 28 counties and parishes in six states had soybean rust.
Oklahoma rust report
Oklahoma officials reported today that "both new finds were were on MG3 soybeans at R6. Rust continues to increase in the Bryan County sentinel plot, where rust reached an incidence of over 50%. Sentinel plots in Choctaw (where rust was found in a commercial field), Okmulgee, Ottawa, Sequoyah, Tulsa, Wagoner, and Washington Counties remained negative for rust last week. Rust also has not been found in observational samples taken from commercial fields in Garvin, Pottawatomie, and LeFlore Counties.
"Beginning this past weekend through next weekend, conditions are not expected to favor rust development. Hot, windy conditions are expected to prevail state-wide, with temperatures reaching triple digits in some areas. Other diseases such as downy mildew, brown spot, bacterial blight, and frogeye leaf spot are widespread and continue to make rust recognition difficult."
Regarding rust management, the commentary 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. Most early maturing varieties are at R5 to R6, and the decision to spray at R5 is a judgment call. Full-season varieties are currently at risk for damage to soybean rust. However, weather conditions are not expected to favor rust increase this week, and it may be possible to delay applications to a later growth stage. Furthermore, moisture stress is likely to be a factor in many areas if the weather forecast holds."
More soybean rust in SW Arkansas
While no new commentary was posted today, Arkansas did turn two more counties red: Lafayette and Miller counties are positive for rust. They are in the far southwest corner of the state, just below previously positive Hempstead and Little River counties.
Florida finds rust in Escambia County; it spreads in Gadsden County
Per today's Florida state commentary:
"Rust has been confirmed in a single sentinel plot in Escambia County. A sample, originally collected July 23, was incubated for a week before sporulating pustules were visible. The sample was confirmed with PCR on Aug. 3. Escambia County is adjacent to an already-positive county in Alabama (Baldwin County).
"A new plot at the NFREC in Gadsden County has been found to be infected with rust. It is about 1/4 mile from the previously reported site. It is a sentinel plot with MGIII, V, and VII in various reproductive stages. As part of cooperative study, several different spore traps were located adjacent to the plot.
"To enhance the chance of correlating the spore trap results with disease, 1/2 of each plot was misted for 18 hours (1/2 min per 30 min through the night). We have found rust in the misted side and the non-misted side. The sentinel sites at this location became positive in July in 2006 and August in 2005. We have not yet heard back if the spore traps have detected anything.
"These plots are repeated in Louisiana and South Carolina as part of a regional study. Two other sentinel plots on the station about 1/2 to 3/4 of a mile away from the positive plots are still negative - they do not have mist systems in them. This brings the number of positive soybean sentinel plots to three: Marion County in central Florida, and Gadsden and Escambia Counties in the panhandle.
"Although we are in a more typical rain pattern, we are still 20 inches below normal," officials said. "Still there is a lot of humidity; dew is present; and (there are) near-daily local showers. It is warm for rust to be at optimum, but rainfall is probably not limiting anymore."
2007 rust counties total more than double 2006 tally
Here are the counts of positive rust counties and parishes for 2007, by state in descending order: Texas 24 (23 on soybean), Florida 11 (two soybean), Louisiana 7 (6 soybean), Alabama 5 (one soybean), Georgia 5 (all kudzu), Arkansas 4 (all soybean), Oklahoma 4 (all soybean), Mississippi 1 (kudzu), for a total of 61 with 40 of the counties/parishes having rust on soybean.
At this point in the 2006 season the counts were: Florida 13, Georgia 5, Alabama 5, Louisiana 3, Mississippi 1, Texas 1 for a total of 28. Only eight of those finds were on 2006 soybeans; the one in Texas was on old-crop soybeans and the rest were all on kudzu.
Source: State commentaries on www.sbrusa.net, the USDA Pest Information Platform for Extension and Education.
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