GRAY LEAF SPOT

gray leaf spot on tall fescue	Characteristic	Description
	Host Grass Species	tall fescue, perennial ryegrass, and St. Augustinegrass
	Month(s) with symptoms	July, August, September
	Stand Symptoms	spots, patches (4 to 12 inches)
	Foliar Symptoms - Location/Shape	round or oval leaf spots
	Foliar Symptoms - Color	tan, gray
	Root/Crown Symptoms	none
	Fungal Signs	none or fuzzy spore masses

 

Note: Still not sure if this is the right disease? The Turfgrass Disease Identification program may be helpful. Or consult the experts at the Turf Diagnostics Lab. Check the TurfFiles glossary for definitions of unfamiliar terms.

FACTORS AFFECTING DISEASE DEVELOPMENT

Gray leaf spot is most severe in newly established turfgrass stands. The disease is typically most severe in the first year of establishment, but then gradually becomes less damaging as the turf matures.

Turfgrass hosts vary widely in their susceptibility to damage from gray leaf spot. Perennial ryegrass is most rapidly affected by the disease, with widespread turf loss occurring in a period of a few days. St. Augustinegrass is most resistant, and rarely sustains significant damage if properly managed. Tall fescue has an intermediate level of resistance to gray leaf spot. In St. Augustinegrass, gray leaf spot is most active from June through August. In tall fescue and perennial ryegrass, most cases of the disease appear from late July through September.

Gray leaf spot may develop when temperatures are between 70 and 95°F, but the fungus also requires at least 14 hours of continuous leaf wetness in order to initiate infection. Any factor that increases the amount of leaf wetness will increase gray leaf spot development. Lush leaf tissue produced by turf that is fertilized with excessive nitrogen is extremely prone to infection by the gray leaf spot pathogen.

CULTURAL CONTROL

Cultivars of tall fescue and St. Augustinegrass vary considerably in gray leaf spot susceptibility. Refer to local University recommendations for cultivars with gray leaf spot resistance that perform well in your area. Perennial ryegrass cultivars with resistance to gray leaf spot are not currently available, but may be in the near future.

Managing leaf wetness is an effective means for minimizing gray leaf spot in all hosts. Irrigate deeply and infrequently, applying sufficient water to wet the entire root zone and repeating only when the entire root zone is no longer moist. Schedule irrigation early in the morning, before sunrise, and never in the late afternoon or evening. Prune or remove trees, shrubs, or other barriers to increase air movement and sunlight penetration.

Proper mowing practices are most important for gray leaf spot management in St. Augustinegrass. This grass must be mowed frequently during the summer months to remove excess leaf tissue, keep the canopy open and dry, and remove developing gray leaf spot lesions. Collecting clippings reduces spread of the disease when gray leaf spot symptoms are evident. Apply nitrogen and other nutrients as recommended to maintain vigorous foliar growth during the summer months. Excessive shade, in addition to promoting leaf wetness, slows St. Augustinegrass growth and enhances gray leaf spot problems.

Stress of any kind will encourage gray leaf spot development in tall fescue and perennial ryegrass. Proper mowing, fertilization, and irrigation practices will reduce the chances of significant turf loss from this disease. Mow to recommended heights, using the “1/3 rule” as a guide for mowing frequency. Collect clippings when gray leaf spot is active to reduce further spread of the disease. Do not apply nitrogen to susceptible grasses in late spring or summer. When establishing a new stand of tall fescue or perennial ryegrass, use recommended seeding rates to allow rapid maturation of new seedlings.

CHEMICAL CONTROL

Since perennial ryegrass can sustain serious damage in a short period of time, preventative fungicide applications are recommended for gray leaf spot control. A preventative program should be initiated in mid-June or early-July in most locations, with repeat applications on a 14 to 21 day interval. Tall fescue should be monitored frequently for gray leaf spot development so that fungicides can be applied to stop epidemic development. Fungicides are usually not necessary for gray leaf spot control in St. Augustinegrass if the turf is properly maintained.

© North Carolina State University. This information sheet was prepared by Fred Yelverton, Gail G. Wilkerson, Leon Warren, Travis Gannon, and Gregory S. Buol. Department of  Crop Science, College of Agriculture & Life Sciences, North Carolina State University. Prepared November, 3, 2008. Available on-line at www.turffiles.ncsu.edu. This publication was made possible through a grant provided by the Center for Turfgrass Environmental Research & Education (CENTERE) whose purpose is to support worthwhile projects that will benefit both the private sector and the public, and protect the environment.