Pest Alert №15 — X-Files: Gray Leaf Spot in Chicago?
Beginning in early October, it seemed as if the usual melting out caused by Drechslera, Bipolaris and other leaf spot fungi was developing in Chicago’s rough height turfgrasses. Leaf spots are a normal event each spring and fall. Certain Kentucky bluegrass varieties (older ones) are highly susceptible.
Instead, after 24 hours of incubation, the distinctive spores of Pyricularia grisea were observed. This proved that gray leaf spot, a disease we have learned to expect in the transition zone each growing season (such as central Illinois), could also be impactful further north. We are talking all the way up into the north suburbs of Chicago. Impressive to say the least, because it was the third surprise of the 2021 growing season. The first surprise was my return to Chicago. The second was the appearance of fall army worms (though no real damage from that insect occurred in Chicago). X-Files stuff.
In the U.S., gray leaf spot is thought to be relatively rare in the northern most states. Gray leaf spot had not previously been identified in Chicago. For example in the 1990s gray leaf spot made its first appearance and decimated perennial ryegrass fairways and roughs (personal communication with Dr. Randy Kane). RK suggests Climate Change? Perhaps shifts in the weather from previous norms are to blame? For example, warm weather extended into the third week of October during the 2021 growing season.
The host negatively affected was no surprise. It was perennial ryegrass. A beautiful grass, but it comes with many issues as far as diseases go. Previously perennial ryegrass was known as the magnet for Pythium blight (P. aphanidermatum). To this day many golfers know one Latin word for fungal disease and they will say it with gusto “Pythium”. Nevertheless Pythium blight wasn’t the end of perennial ryegrass. It was a second. Use of perennial ryegrass in fairways largely ended because of gray leaf spot. It was the gray nail in the coffin so to speak. It then paved the way for expanded (tee to green) use of creeping bentgrass.
