Integrated Crop Management

Soybean rust update -- August 2005

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
Florida Pasco 2/25/2005 Kudzu Low
Florida Hernando 3/22/2005 Kudzu Low
Florida Marion 4/8/2005 Kudzu Low
Georgia Seminole 4/27/2005 Vol. Soybeans Low
Florida Dade 4/29/2005 Kudzu Low
Georgia Terrell 5/27/2005 Vol. Soybeans Low
Florida Jefferson 6/15/2005 Kudzu Low
Florida Leon 6/27/2005 Kudzu Low
Alabama Baldwin 6/28/2005 Sentinel Plots 75–100% Incid. by 7/12 Bloom and R6
Florida Marion 7/1/2005 Sentinel Plot Low R2–R3
Florida Gadsden 7/6/2005 Kudzu Low
Alabama Baldwin 7/12/2005 Commercial SB Low
Mississippi George 7/13/2005 Sentinel Low R5–R7
Georgia Tift 7/18/2005 Sentinel Plot Low R5
Florida Escambia 7/19/2005 Sentinel Plot Low R4
Georgia Decatur 7/21/2005 Kudzu Moderate
Georgia Decatur 7/22/2005 Sentinel Plot Low R4–R5
Georgia Colquitt 7/26/2005 Sentinel Plot Low R4–R5
Florida Hamilton 7/29/2005 Kudzu Low
Georgia Brooks 7/29/2005 Private Research Low
Georgia Effingham 7/29/2005 Sentinel Plot Low
Alabama Lee 7/29/2005 Research Plot 30% Incid., Low Sev. R5–R6
Florida Hamilton 8/2/2005 Commercial SB Low R5
Alabama Elmore 8/3/2005 Sentinel Plot 60% Incid., Low Sev. R5–R6
Georgia Tift 8/3/2005 Research Plot Heavy in Focus Area R5
Georgia Tift 8/5/2005 Research Plot Profuse Sporulation R3
Georgia Laurens 8/5/2005 Sentinel Plot Low R5
Florida Hamilton 8/4/2005 Kudzu Small, Moderate
Florida Alachua 8/4/2005 Kudzu Small, Light
Florida Lee 8/8/2005 Kudzu
Alabama Escambia 8/8/2005 Sentinel Plot 20% Incid., Low Sev. R5
Florida Holmes 8/10/2005 Sentinel Plot Low? R5+
Florida Oskaloosa 8/10/2005 Sentinel Plot Low? R5+
Florida Santa Rosa 8/10/2005 Sentinel Plot Low? R5+
Alabama Baldwin 8/10/2005 Kudzu
Florida Taylor 8/11/2005 Kudzu
Florida Columbia 8/11/2005 Sentinel Plot Low? R5+
Florida Hillsborough 8/11/2005 Kudzu
Alabama Baldwin 8/11/2005 Commercial SB 5 Fields, V. Light–Mod. R4+
South Carolina Hampton 8/15/2005 Commercial SB Low R3/4
Georgia Putnam 8/16/2005 Kudzu
Alabama Baldwin 8/17/2005 Kudzu
Alabama Talladega 8/18/2005 Sentinel Plot and
Commercial SB
Low R6�Sentinel,
Georgia Sumnter 8/19/2005 Sentinel Plot Low R7

Source: Compiled by Kevin Black, GROWMARK, Inc.

Infection in soybean leaflet

Asian soybean rust pustules on underside of susceptible soybean leaflet. It is a great relief�as well as a surprise�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.

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