(Megan Kennelly, KSU Plant Pathology)
Gray leaf spot is a serious disease of perennial ryegrass that can quickly blight large areas of turf. The disease is caused by the fungus Pyricularia grisea. In Kansas, turfgrass managers with perennial ryegrass often spray fungicides preventatively right around now, in early to mid August, sometimes with a follow-up application (or 2) to provide protection through September, depending on weather. This year, I’ve heard some reports that people have seen activity earlier than usual, which is definitely possible with all the rain.
This disease can be so bad that a lot of golf courses have switched to other turfgrass species (zoysia, bluegrass, bent – though bent has some nasties, too) so that they don’t have to worry about it in their fairways.
Here is a fairway that went from healthy to severely damaged in a short time, a couple of years ago. They switched to Kentucky bluegrass.
The fungus sporulates profusely and can spread fast when weather is conducive to disease (82-90 degrees with humidity and leaf wetness). Here are some of the spores in the microscope from a sample I got a couple of years ago:
Early symptoms look like this – small leaf spots the color of a Hershey bar:
(Photo courtesy Ned Tisserat, Colorado State University, Bugwood.org)
The spots grow and develop a gray center.
If you are managing rye, you are probably already thinking about gray leaf spot, and maybe you’ve just done your first app or have it on the docket soon. For some more details on management and fungicides, check out the gray leaf spot section (starts on p. 13) in this publication:
http://www2.ca.uky.edu/agc/pubs/ppa/ppa1/ppa1.pdf
There are more photos and details on the disease at this website as well, from an excellent publication by Barb Corwin and my predecessor Ned Tisserat:
http://extension.missouri.edu/p/IPM1029-11#Grayleafspot
Now – I gotta get back into the lab. I’ve got some more sick turf, a dying chrysanthemum, and a really nasty potato (mushy and stinky – eewww) to deal with by the end of the day.
