Quick Facts

Extended Version | Download fact sheet

Soybean Rust

Causal Agent:

Phakopsora pachyrhizi

Symptoms and Signs:

  • small, tan to brick-red spots on leaves
  • pustules develop from spots,  containing spores
  • symptoms will begin in lower canopy and progress upward
  • leaves will turn yellow, die, and drop prematurely

Disease Cycle:

  1. The pathogen overwinters in the gulf coast area of the United States. For inoculum to travel to Ohio, it would need to be blown by a hurricane several hundred miles.
  2. Urediniospores travel by wind to suitable hosts.
  3. The spore will infect within 12-14 hours in wet conditions and temperatures between 60-78 degrees.
  4. Spots on leaves will appear approximately 4 days after infection, and pustules soon follow about 1 week later.

Disease Management:

It is important to monitor the risk of SBR by checking its distribution in the southern U.S. The best time to check distribution is when soybeans begin to flower. Land grant universities and the United Soybean Board collaborate to maintain a network of sentinel plots across the U.S. These sentinel plots include naturally occurring kudzu patches or soybean plots planted weeks before commercial soybean fields are typically established in an area. The sentinel plots  are scouted weekly for SBR and act as an early warning systems for growers in that region. Observational data is collected from each plot and uploaded to a central site which then provides real-time maps showing rust activity across the country. Information about sentinel plots can be found at http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi.