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July 10, 2013

These are pictures of Summer Patch on Kentucky bluegrass at the Horticulture Research Station.  It is caused by the fungi Magnaporthe poae.  It typically shows up in early summer, particularly in years like this that are very wet early followed by a quick drying period and hot temperatures.  This showed up over the 4th of July (right on time).

The blighted areas with a green center that are surrounded by a circle of dead grass are known as “frog-eyes” and are typical of a number of patch diseases.  It is believed that the organism begins as a saprophyte (organism that feeds on dead plant material) in the middle and moves outward in a circle without damaging living grass.  It only attacks living grass if conditions are right and it reaches a certain level of virulence. The patches here are 10 to 12 inches in diameter, which is common for this disease.

There are several systemic fungicides labeled for this disease, but the trick is to get them down before the symptoms develop.  Contact fungicides will not work.  To treat now would do no good and the symptoms will like last through the summer.  This is a disease for which good records are a must.  On this area, I would need to apply a systemic fungicide in late June next year before symptoms develop.  Core aeration in the fall and irrigation during the stress period of early summer can also help prevent its development.




September 24, 2012

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  (  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.