As of today, soybean rust has been found in only five southern states: Alabama, Florida, Georgia, Mississippi, and South Carolina. The disease was found in sentinel plots, commercial production fields, and kudzu plants (see table below). In regions beyond these states, spores that look like spores of soybean rust have been detected by a spore-monitoring project led by the University of Arkansas. A lot more such spores have recently been found in many southern states. In Iowa, no soybean rust has been found in our latest scouting, both in sentinel plots and some production fields.
What is the risk for the rest of the season?
For the north-central states, the window of having soybean rust with severity to cause significant damage has been over for a while. In a July soybean rust outlook by our research group, we suggested that the risk of having a soybean rust epidemic was minimal because of dry weather in the Midwest soybean production region and slow development of the disease in the South. However, the window of observing soybean rust is not over yet for some north-central states that have a longer growing season than Iowa. As for Iowa, the chance of finding the soybean rust depends on when the rust reaches Kentucky and Arkansas.
What is the risk for next year?
It is a great relief--as well as a surprise--that soybean rust has not reached the major soybean production regions. It had been anticipated that the occurrence of soybean rust will be sporadic in the continental United States once the disease establishes itself. However, the development of soybean rust in this season has been much slower than many experts had predicted. The disease was first found in Missouri last fall when it arrived on Hurricane Ivan in September. In this season, the disease so far has not been found in Tennessee, although the disease showed up in Florida even before March.
Besides dry weather, other factors, which are yet to be determined, may have slowed the development of soybean rust. The American Phytopathological Society is organizing a national meeting in November, which is open to people of all sectors, to summarize what we learned from this season and assess the risk for future seasons.
2005 Soybean Rust Infection Summary
|State||County||Approximate Date||Host Plant||Infection Level||Developmental Stage|
|Alabama||Baldwin||6/28/2005||Sentinel Plots||75Ã¢â‚¬â€œ100% Incid. by 7/12||Bloom and R6|
|Alabama||Lee||7/29/2005||Research Plot||30% Incid., Low Sev.||R5Ã¢â‚¬â€œR6|
|Alabama||Elmore||8/3/2005||Sentinel Plot||60% Incid., Low Sev.||R5Ã¢â‚¬â€œR6|
|Georgia||Tift||8/3/2005||Research Plot||Heavy in Focus Area||R5|
|Georgia||Tift||8/5/2005||Research Plot||Profuse Sporulation||R3|
|Alabama||Escambia||8/8/2005||Sentinel Plot||20% Incid., Low Sev.||R5|
|Florida||Santa Rosa||8/10/2005||Sentinel Plot||Low?||R5+|
|Alabama||Baldwin||8/11/2005||Commercial SB||5 Fields, V. LightÃ¢â‚¬â€œMod.||R4+|
|South Carolina||Hampton||8/15/2005||Commercial SB||Low||R3/4|
|Alabama||Talladega||8/18/2005||Sentinel Plot and |
Source: Compiled by Kevin Black, GROWMARK, Inc.
Asian soybean rust pustules on underside of susceptible soybean leaflet. It is a great reliefÃ¢â‚¬â€?as well as a surpriseÃ¢â‚¬â€?that soybean rust has not reached the major soybean production regions this season. (X. B. Yang)
This article originally appeared on pages 170-171 of the IC-494(22) -- August 22, 2005 issue.