The Purdue Plant and Pest Diagnostic Laboratory

Asian Soybean Rust
Phakopsora pachyrhizi


USDA Public Soybean Rust Web Site

Purdue University Soybean Rust Hotline - 866-458-RUST (7878) phone

Preparing for Soybean Rust (pdf file) - Purdue publication, order hard copies here


Soybean rust was confirmed June 10, in the US for the first time this season on soybean in Hidalgo county, Texas. Rust has also been confirmed on soybean in the neighboring Mexican state of Tamaulipas. Soybean rust has also been confirmed this month (June) on kudzu in Mobile, Alabama, and Jefferson, Florida.

In 2009, soybean rust was found in 16 states and over 576 counties in the United States, and in three states and nine municipalities in Mexico.

Soybean rust was found in 392 counties in the United States in 2008. This is the highest number of counties reporting the disease since it was first discovered in the continental U.S. in 2004.

Asian soybean rust (ASR) is a serious disease caused by the fungus Phakopsora  pachyrhizi. Soybean rust is spread by windblown spores and has caused significant crop losses in many soybean-growing regions of the world (pdf file). On November 10, 2004 USDA's Animal and Plant Health Inspection Service (APHIS) announced the first confirmation of Asian soybean rust in the continental United States (Louisiana), followed by finds in 8 additional southern states. In 2005, soybean rust was confirmed on soybeans in 29 counties in Georgia, 23 counties in South Carolina, 21 counties in Alabama, 18 counties in North Carolina,12 counties in Florida, 2 counties in Mississippi, and one county in Louisiana. 

Phakopsora pachyrhizi is an obligate parasite, meaning that it must have live, green tissue to survive. The host range of the soybean rust fungus is quite broad.  In addition to soybeans, the ASR fungus is able to infect over 30 legumes including edible bean crops and kudzu. In November 2005, P. pachyrhizi was confirmed on Florida Beggarweed (Desmodium tortuosum) in Georgia. These additional hosts can serve as overwintering reservoirs for the pathogen and allow for build-up of inoculum, in those environs free from freezing temperatures.  The pathogen is well adapted for long-distance dispersal, because spores can be readily carried long distances by the wind to new, rust-free regions.

Early symptoms appear as chlorosis and brown flecking on the lower leaves in the canopy. Developing lesions can be confused with symptoms caused by other foliar diseases, such as bacterial pustule, bacterial blight, downy mildew and Septoria brown spot. The key diagnostic features of soybean rust are the cone-shaped pustules that form mostly on the undersides of the leaves and the dusty, light-tannish colored spores that erupt from the pustules. When untreated, soybean rust, causes yield losses due to premature defoliation, fewer seeds per pod and decreased number of filled pods per plant.  For state-specific information on diagnosing the presence of soybean rust contact your state's land-grant university diagnostic clinic (pdf file).


Fact Sheets/Articles

Rust ID/Sample Submission

Soybean Rust - PowerPoint Presentations

News Articles


  • Dr. Kiersten Wise ( ), Extension Plant Pathologist and Soybean Rust Specialist, Department of Botany & Plant Pathology, Purdue University
  • Dr. Greg Shaner ( ), Retired Extension Plant Pathologist and Soybean Rust Specialist, Department of Botany & Plant Pathology, Purdue University
  • Dr. Corinne Alexander ( ), Assistant professor, Department of Agriculture Economics, Purdue University
  • Dr. Ray D. Martyn ( ), Professor of plant pathology, Botany & Plant Pathology, and Director of the Center for Crop Biosecurity, Purdue University
  • Plant and Pest Diagnostic Laboratory ( )
  • Gary W. Simon ( ), Indiana State Plant Health Director
  • Dr. Phil Marshall ( ), Indiana State Plant Regulatory Officer, IN Department of Natural Resources - Director of the Division of Entomology & Plant Pathology

Forecasting & Tracking












Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service