National Soybean Rust Commentary 
(updated: 06/06/06)

Scouting has intensified in soybean sentinel plots especially in the south. Most of the soybean sentinel plots have been planted throughout the country with plants in some early planted plots starting to reach maturity. Scouting continues on kudzu patches from Florida to the north as far away as Nebraska. A recent limited survey of kudzu in Florida found no evidence of abundant infection or sporulation. Currently, there are no known reports of rust on commercially planted soybean in 2006. Rust has been confirmed in five counties in Alabama, 11 in Florida, four in Georgia, and one in Texas. Many of the Southern states are experiencing hotter and drier than normal conditions reducing the likelihood of viable spore dispersal. A report regarding Mexico indicated that rust had occurred earlier in the year (winter season seed production) before any commercial soybeans were planted in Mexico or the U.S. Spore trapping continues throughout the U.S. using both active and passive traps. Any positive spore trap information does not imply infection has taken place and plant samples are used exclusively for indicating positive rust occurrence as indicated on the soybean rust observation map.

A few comments on the April rust reports from Mexico. These reports centered on the Mexican states of Tamaulipas and San Luis Potosi, which are located on the gulf coast just south of Brownsville, TX (Figure 1). Though further comments and discussion regarding the Mexico situation have been quiet, it is known that no rust has been confirmed in Texas where dryer than normal weather is occurring and therefore not conducive to soybean rust development.

Why concern about Texas and Mexico? Wind patterns that affect Minnesota are more likely to flow through Mexico and Texas during the summer. These routes may provide a more direct route to Minnesota when compared to weather patterns passing through southeastern states. Perhaps, soybean rust will follow the known pathway of other rust diseases, such as cereal leaf rust (Puccinia triticina).

 

Local Reports for Minnesota and North Dakota

In Minnesota, 25 soybean rust sentinel plots have been established in 2006. Placement of the plots throughout the state is based on distribution of soybean acreage and expected environmental conditions that may favor soybean rust. The sentinel plots are located in the following counties: Blue Earth, Dakota, Freeborn, Goodhue, Houston, Jackson, Marshall, McLeod, Nicollet, Nobles, Norman, Olmsted, Otter Tail, Pipestone, Polk, Ramsey, Redwood, Renville, Sibley, Stearns, Stevens, Swift, Waseca (2), and Wilkin. Scouting has begun in many of the sentinel plots. Leaf samples will be collected from each plot throughout the season and sent to a central laboratory at the University of Minnesota in St. Paul for analysis and diagnosis. There appears to be no foreseeable significant risk of soybean rust developing in Minnesota at any time in the near future.

In North Dakota, Soybean plants within the state are at 97% planted and 68% emerged according to USDA-NASS-ND. Growth stages currently range from not emerged to V2. Sentinel plot plantings have completed and monitoring will begin soon. Currently, no scouting or management for soybean rust is required in North Dakota.

INFORMATIVE SOYBEAN RUST WEBSITES:

USDA Soybean Rust Public Information
http://www.sbrusa.net/

North American Plant Disease Forecast Center
http://www.ces.ncsu.edu/depts/pp/soybeanrust/

Soybean Rust Pest Tracker
http://ceris.purdue.edu/napis/pests/asbr/index.html