By Mike Agnew, Ph.D., technical services manager for Syngenta

Cultural Practices | Treatment Options | Data | Disease ID Guide

The development of gray leaf spot in the transition 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.

The disease, gray leaf spot, is caused by the organism Pyricularia grisea (also known as Magnaporthe grisea) and 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 at least 14 hours of 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 reddish brown lesions on leaf blades (image A), tip dieback, general blighting not specific to high or low areas, a twisted or “fishhook” appearance (particularly on new leaves) and a fuzzy appearance on leaves early in the morning. Like the leaf spots, these patches rapidly coalesce to produce large, irregularly-shaped areas of damaged turf that could resemble Pythium blight (image B).



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.

Treatment options

Heritage^® Action^™ and Banner Maxx^® II fungicides are among the most effective systemic fungicides for gray leaf spot control. Ascernity^® and Posterity^® XT fungicides are newer entries into the market that have also proven to provide solid control. Because gray leaf spot can and will develop resistance to fungicides, tank-mixtures with a multisite contact fungicide, such as Daconil Ultrex^®, Daconil Weatherstik^® or Daconil^® Action fungicides, is recommended. 

See the Efficacy Chart as part of the Syngenta Disease ID guide. 

Ascernity and Posterity XT fungicides have demonstrated excellent gray leaf spot control in trials conducted in Maryland. 

For more information on gray leaf spot rates and tank-mix combinations, learn about agronomic programs available from Syngenta.

​​​​​​​All photos are either the property of Syngenta or are used with permission.

Product performance assumes disease presence.

© 2021 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties and/or may have state-specific use requirements. Please check with your local extension service to ensure registration and proper use. Action™, Ascernity^®, Banner Maxx^®, Daconil^®, Daconil Ultrex^®, Daconil Weatherstik^®, Heritage^®, Posterity^® and the Syngenta logo are trademarks of a Syngenta Group Company.