Here are some pictures of rust disease on Kentucky bluegrass submitted by Damian Richardson, Landscape and Conservation Specialist from Alden, IA. Rust is caused by fungi in the genus Puccinea. It is common on Kentucky bluegrass and other grass species in Iowa, but there has not been a lot of it so far this year. It usually begins to show up about the first of August. This is the first report of it that I have received this year. This one was on September 20. These are some good closeups of the rust pustules on the individual blades of grass. Thanks for submitting them Damian.
While there are several fungicides that will control rust, I usually do not recommend chemical treatment unless it is on a critical area. It is usually a sign of relatively low nitrogen. Just add a little nitrogen and mow regularly and the problem should run its course and disappear. Some cultivars of Kentucky bluegrass are more susceptible that others. If it is a continuous problem each year, you may want to kill the existing cultivars with Roundup and replace them with more tolerant varieties. For information on which varieties show tolerance of rust, see the National Turfgrass Evaluation (NTEP) web site at (http://www.ntep.org/). They have data over several years on rust infestation of many cultivars of Kentucky bluegrass.
If anyone else is seeing a lot of rust, let me know.