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Six new parishes in Louisiana have soybean rust on soybeans
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8/9/2007 Noon CDT -- Asian soybean rust has been found in six new parishes in Louisiana -- spread from the northwest corner of the state down through the center to the southwest. All was on soybeans, both in sentinel plots and in commercial fields.
In Oklahoma, rust was found in a Tulsa County sentinel plot, but officials say not to spray fungicides this week due to the extreme heat.
Per the Louisiana commentary today:
"On Monday, Aug. 6, the parishes of Jefferson Davis, Allen and Evangeline were found to have soybeans positive to Asian soybean rust. In J. Davis and Evangeline parishes, the rust was found in sentinel plots, but the disease was found in commercial fields in J. Davis and Allen Parishes. These are all southwest Louisiana parishes.
"On Wednesday, Aug. 8, ASR was found in the sentinel plot in Concordia Parish and in commercial beans in East Baton Rouge Parish. Concordia is in East Central Louisiana, and E. Baton Rouge is along the Mississippi River and includes Baton Rouge and the LSU campus.
"Today, Thursday, ASR was confirmed in the sentinel plot in Bossier Parish, in the northwest portion of the state."
Officials said scouting continues across the state. Applications of fungicides continue statewide. The targets include the traditional diseases plus ASR.
Louisiana now has 13 parishes positive for soybean rust. There are 68 counties and parishes with soybean rust in the U.S. so far this year, vs. 29 on this date in 2006.
Oklahoma has more rust; spraying not recommended due to heat
Yesterday, Oklahoma reported that soybean rust was found in Tulsa County in a sentinel plot at R6 at an incidence of 1%. Tulsa County juts up farther than Payne County, so it nudges it out for the farthest-north rust has been found this year. Rust was also found in the sentinel plot in Choctaw County (where rust was found earlier in a commercial field) at 2% on MG6.6 soybeans at R1.
Rust incidence increased in the sentinel plots in Payne County from 1% to 8% in R6 soybeans and was found in R3 soybeans at 2%. Sentinel plots in Okmulgee, Ottawa and Washington counties remained negative for rust this week. Several irrigated fields in Muskogee County were also visited and found to be negative for rust this week.
"Current weather conditions and those forecasted for next week will favor neither rust or crop development. Hot and 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.
John Damicone, Extension plant pathologist at Oklahoma State University, said in his official management recommendation:
"I am suspending fungicide recommendations for rust this week. Excessive heat approaching triple digits is not conducive to further rust development and soybeans are beginning to show signs of moisture stress. Fungicide application to heat and drought stressed soybeans is not likely to prove productive. Decisions to spray for rust should be reevaluated when the weather moderates after considering crop condition and yield prospects."
Kentucky specialist takes stock of risk
In an e-mail to colleagues today, University of Kentucky plant pathologist Don Hershman had the following to say about the most-recent rust finds:
"There has been a small “explosion” of finds in Louisiana today and a new find in north central Oklahoma. None of these finds are surprising, and we are still in a holding pattern in KY.
"Spores could be moved into Kentucky any time now if a tropical or mid-latitude storm system moves through the lower midsouth and into Kentucky. This said, there continues to be absolutely NO REASON to apply a fungicide for soybean rust management in Kentucky at this time. If enough spores do make it here and the conditions favor infection, it will take 10 to 14 days for us to see evidence of disease following spore deposition and infection. Initially, the incidence and severity levels will be very low.
"Once we see evidence of low levels of soybean rust in or very near Kentucky, then would be the time to begin making fungicide applications, but not until then. In my opinion, the absolute earliest we may need to treat here is late-August. By that time, most full-season crops will be well into pod fill and may not need to be treated. Double-crop beans continue to be at the greatest risk for possible damage by SBR.
"Of course, if no tropical storms or multi-day wet periods pass through Kentucky during August, we may end up with a repeat of 2006 where no spraying for SBR was needed."
Source: Louisiana and Oklahoma state commentaries on www.sbrusa.net and e-mail from Don Hershman, University of Kentucky.
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