Gray leaf spot management
By Lisa Beirn, Ph.D., technical services manager for Syngenta
The development of gray leaf spot in the transition zone and northern climates has changed the management of perennial ryegrass forever. Perennial ryegrass was first adopted by turfgrass managers because of the better tolerance to fairway and tee mowing heights versus Kentucky bluegrass. Coupled with a rapid germination rate that allows for quick cover following overseeding, perennial ryegrass began quickly replacing Kentucky bluegrass. Beginning in the early 1990s, however, a disease once known to attack St. Augustinegrass in the south began to ravage perennial ryegrass in the north.
Gray leaf spot is caused by the fungus Pyricularia oryzae, and it can infect both perennial ryegrass and tall fescue. Gray leaf spot often appears on golf courses, athletic fields and other turf areas throughout many parts of the U.S. This devastating pathogen is believed to become active and colonize during late spring or early summer, with plant damage appearing late summer into the early fall. Air temperatures between 70 F and 95 F and periods of extended leaf wetness will increase gray leaf spot development. Lush leaf tissue produced by over-fertilized turf is extremely susceptible to infection by the gray leaf spot pathogen.
Symptoms may include:
Small gray to tan lesions with a reddish-brown border (image A)
General blighting not specific to high or low areas
A twisted or “fishhook” appearance (particularly on new leaves)
A fuzzy appearance on leaves early in the morning.
Infected patches can rapidly coalesce to produce large, irregularly shaped areas of damaged turf that could resemble Pythium
blight (image B). Left photo courtesy of Lane Tredway, 2005. Right photo courtesy of Steve McDonald, Turfgrass Disease Solutions.
Beneficial cultural practices include:
- Reducing periods of leaf wetness in perennial ryegrass and tall fescue. Schedule irrigation in the early morning before sunrise and never in the evenings.
- Improving air circulation, which will decrease the potential for disease development. Prune or remove barriers to increase air movement and sunlight penetration.
- Avoiding plant stress from soil compaction, drought and other diseases. Plant stresses will encourage gray leaf spot development.
- Providing adequate balanced fertility, but not excessive nitrogen.
- Avoiding core cultivation and overseeding procedures during periods of potential infection.
Source: Dr. Joseph Doherty, University of Maryland, 2020. Treatments applied on June 29, July 25, July 29 and Aug. 12, 2020. Data collected on July 13, July 27, Aug. 10 and Aug. 24, 2020.
For more information on gray leaf spot rates and tank mix combinations, learn about agronomic programs available from Syngenta.
Product performance assumes disease presence.
All photos are either the property of Syngenta or are used with permission.
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