Gray leaf spot management
By Mike Agnew, Ph.D., technical services manager for Syngenta
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.
Heritage®, Heritage® TL, Heritage® Action™ and Banner Maxx® II fungicides are among the most effective systemic fungicides for gray leaf spot 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, is recommended.
The data in the graph below demonstrates excellent control of gray leaf spot with the following:
- Heritage TL
- A combination of Heritage TL and Daconil Ultrex
- Heritage Action
- A combination of Heritage Action and Daconil Action
- Pre-mix products, such as Briskway®, Headway®, Concert® II and Renown® fungicides, are also effective options to consider
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.
©2020 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™, Banner Maxx®, Briskway®, Concert®, Daconil®, Daconil Ultrex®, Daconil Weatherstik®, Headway®, Heritage®, Renown® and the Syngenta logo are trademarks of a Syngenta Group Company.