Agronomy Mimeo 84Revised April, 1997

INTRODUCTION

TURFGRASS MANAGEMENT PRACTICES

Irrigation provides moisture critical to fungal spore germination and growth. The timing, duration and frequency of irrigation may greatly affect disease intensity. Light, frequent irrigations discourage root development and predispose turf to injury when extended periods of drought occur. Drought stress appears to favor Helminthosporium diseases, stripe smut, powdery mildew, summer patch, dollar spot, and fairy rings. Excessive irrigation also restricts root development and encourages disease. Turfgrasses grown under wet conditions develop succulent tissues and thinner cell walls, which presumably are more easily penetrated by pathogens. Algae and mosses thrive in waterlogged soils, particularly where turf density is poor. Morning or early afternoon irrigation is recommended during summer to insure that plant tissues are dry by nightfall. Morning irrigation, when drying occurs quickly, helps to minimize the intensity of Pythium blight and brown patch disease.

Use of proper soil fertility programs improves the vigor of plants and their ability to resist disease. Excessive use of nitrogen has been reported to encourage Helminthosporium leaf spot, brown patch, summer patch, Pythium blight, and powdery mildew. Excessive use of nitrogen promotes tissue succulence and thinner cell walls which, as previously mentioned, are more easily penetrated by fungi. Conversely, turfgrasses grown in nutrient poor soils are prone to invasion by dollar spot, red thread and rust diseases. Application of nitrogen to diseased turf under low fertility conditions stimulates growth at a rate that exceeds the capacity of the fungus to colonize new tissues, thus reducing the level of disease injury. Fall applied nitrogen is recommended for many reasons including disease management. Use of more than modest amounts of nitrogen in the spring can encourage several destructive lawn diseases. See Agronomy Mimeo 90 for the preferred amounts and timings of fertilizer for lawns in Maryland.

Many turfgrass pathogens survive as resting structures or as saprophytes (organisms living on dead organic matter) in thatch. Thatch also provides fungi with moisture. Fungal pathogens such as Helminthosporium spp. produce enormous populations of spores in thatch, particularly when the thatch is subjected to frequent wetting and drying. Stripe smut, Helminthosporium diseases, summer patch, and fairy ring are diseases that appear to be favored by excessive thatch accumulation.

Traffic, like mowing, produces wounds that are easily invaded by some fungal pathogens. Compaction caused by heavy traffic impedes air and moisture movement into soil and eventually restricts root function, causing a decline in plant vigor and disease resistance. Soil pH also may affect disease development in turfgrasses, i.e. extremes in soil pH reduce plant vigor and, therefore, a reduction in the ability of plants to resist disease.

Plant diseases are diagnosed using signs and symptoms. Signs represent the visible parts of the pathogen, e.g. mycelium (the white, thread-like network that comprises the fungus body); fruiting bodies, e.g. mushrooms; resting bodies, e.g. sclerotia; and spores. Symptoms are the outward expression of a plant that is suffering from a disease. Examples of symptoms include leaf spots, tissue blighting, rots, yellowing, wilting and stunting. Symptoms of most turf diseases take the form of leaf spot lesions, blighting of leaves, water-soaking of leaves, and crown or root rots. A symptomatic key to common lawn diseases is provided on the following pages. Control of diseases by the use of fungicides may become necessary in some situations. Fungicides that are recommended for the control of turfgrass diseases are listed in Agronomy Mimeo 80.

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SPOTS ON LEAVES OR LEAF SHEATHS	DISEASE	SEASON	PRINCIPLE HOSTS AND COMMENTS
Leaf spots brown or purple-brown, oval shaped or elongate. The centers of spots may develop a tan color. Turf may be thinning-out in irregular patterns.	Helminthosporium leaf spot	Spring, summer, fall; most common in spring	All turfgrasses, especially common-type cultivars.
Leaf spots are hour-glass shaped, bleached white, tan or straw-brown in color and extend across the entire width of the blade. Leaf lesions are normally bordered by brown, purple or black bands. Affected patches are circular and 2" - 6" in diameter. Foliar mycelium may be evident with a heavy dew in the morning	Dollar spot	Spring, summer, fall; most common in May and June	All turfgrasses, especially poorly nourished turfs.
AFFECTED AREAS DEAD OR THINNING IN CIRCULAR PATCHES, SPOTS OR RINGS
Circular patches of matted leaves appearing late fall, winter, or early spring. Generally appearing at snow melt or in the presence of plenty of surface moisture during cool-cold overcast periods.
1. Patches 1" - 6" diameter; matted leaves have a pinkish or red-brown color. Center of patches may be bleached white in color.	Pink snow mold	Late fall, winter, spring; especially spring	All turfgrasses, especially annual bluegrass, perennial ryegrass, and tall fescue.
2. Patches 6" - 3' diameter; matted leaves have a grayish color. Sclerotia may be present.*	Gray snow mold	Late winter and early spring	All turfgrasses, especially Kentucky and annual bluegrass, and tall fescue.

*Sclerotia are compact masses of fungal mycelium covered with a protective rind. Gray snow mold sclerotia are chestnut brown or black in color, 1/8 - 3/16 inches in diameter, and are usually found embedded in sheaths or on leaves of diseased turf during spring following snow melt.

AFFECTED AREAS DEAD OR THINNING IN CIRCULAR PATCHES, SPOTS OR RINGS (continued)	DISEASE	SEASON	PRINCIPLE HOSTS AND COMMENTS
Circular, straw-brown spots 2" - 6" in diameter. Straw-brown or white, hour-glass shaped lesions on leaves.	Dollar spot	Spring, summer, fall	All turfgrasses, especially poorly nourished turfs.
Circular or irregular patches 3" - 12" in diameter. Leaves watersoaked and covered with a pink gelatinous fungal growth. Dead leaves in center of affected areas straw brown, tan or slightly pinkish in color. Red, brittle, thread-like strands extending from tips of dried grass blades.	Red thread	Primarily spring and fall, and prolonged rainy periods in summer	All turfgrasses, especially perennial ryegrass and fine leaf fescues.
Circular patches 6" - 2' in diameter. Affected areas brown; outer margin of diseased patches may have a grayish "smoke ring." Leaves blighted and oval to elongated, chocolate-brown lesions present. Foliar mycelium evident during early morning when dew is present.	Rhizoctonia brown patch	June-Sept. Normally occurring when night temperatures are above 68 degrees F, high day temps., and high relative humidity.	All turfgrasses, especially perennial ryegrass and tall fescue.
Circular or irregular patches or rings, sometimes rings with living grass in center ("frog eyes"). Patches initially 1" - 2", increasing to 6" - 2' in diameter. Patches may be sunken and leaves at the periphery may have a yellow-orange or bronzed appearance. Tip dieback of leaves giving turf a straw-brown color.	Summer patch	July-early Sept.	Primarily Kentucky bluegrass and fine leaf fescue turfs.
Circular spots 1" - 3" diameter, leaves are grayish or water-soaked, and mycelium is normally present on leaves during early morning hours. Leaves are rapidly blighted and entire plants die in 24 hours. Dead plants in affected spots are brown or red-brown in color, and matted.	Pythium blight	July-early September	Primarily perennial ryegrass especially during hot and humid periods, and in poorly drained sites. Seedlings of all species planted during warm and humid periods are susceptible.
Rings or arcs of dead grass bordered by inner and outer zones of dark green grass; or rings of luxuriantly growing grass without a dead zone. Rings 1 - 4 feet in diameter or larger. Mushrooms, growing in ring, may be present following rainy weather.	Fairy Rings	All year, especially summer	All turfgrass, especially droughty sites and poorly nourished turf.
AFFECTED AREAS DEAD OR THINNING-OUT IN AN IRREGULAR PATTERN
Turf thinning-out and brown or red-brown in appearance from a distance. Brown or purple-brown, oval-shaped leaf lesions on leaves and sheaths.	Helminthosporium melting-out	Primarily during wet, overcast periods in spring and fall.	All turfgrass, especially poorly nourished or excessively fertilized common-types of Kentucky bluegrass and red fescue.
Leaves bearing parallel black or silvery-gray stripes that extend the length of leaves. Leaves eventually shred and curl along lines releasing black, powdery spores masses. Leaves may be yellow.	Stripe or Flag smut	Symptoms noted spring and fall, but turf may succumb during hot, dry periods in summer.	Primarily Kentucky bluegrass older than 3 years of age.
Leaves bearing red, orange, yellow or black pustules. Turf has a yellow or reddish appearance from a distance.	Rust	Primarily late summer and fall	All turfgrasses, especially perennial ryegrass, kentucky bluegrass, and zoysiagrass.
MOLD OR OTHER RESIDUES ON LEAVES
Gray or black, cigarette ash-like residue on leaves. Crusty material (fruiting structures) is easily rubbed off and appears after a prolonged rainy period. Moldy residue may form on plants in rings or arc patterns.	Slime mold	Spring, summer and fall, especially after prolonged rainy periods	All turfgrasses.
Leaves with black or silver-gray stripes that rupture causing leaves to shred and curl; releasing black, powdery spore masses.	Stripe or flag smut	Primarily spring and fall	Primarily Kentucky bluegrass, Kentucky bluegrass and zoysiagrass.
Leaves bearing red, orange, yellow or black pustules. Turf yellow or reddish in appearance from a distance.	Rust	Primarily late summer and fall.	Primarily perennial ryegrass, Kentucky bluegrass and zoysiagrass.
Leaves bearing a whitish or gray moldy growth. Leaves eventually turning yellow.	Powdery mildew	Spring to fall; primarily late summer and fall	All turfgrasses, especially Kentucky bluegrass. Normally occurring on turf in shaded environments.

Tall fescue is widely used as a lawn grass in Maryland. Its strengths include good drought tolerance, moderate fertility needs, and good insect and disease resistance. Tall fescue is susceptible to Helminthosporium net-blotch, crown rust, pink and gray snow mold, red thread, brown patch, and dollar spot. Of these diseases only Helminthosporium net-blotch and brown patch are considered common diseases of tall fescue turf in Maryland. Red thread and dollar spot, however, are becoming more common in tall fescue lawns.

DISEASE	SEASON
HELMINTHOSPORIUM NET BLOTCH Initially, symptoms appear as minute brown or purple-brown specks on leaves. As the disease advances dark-brown, net-like patterns of transverse and parallel lines of necrotic lesions develop on leaves providing a net-blotch appearance. These net-blotches may coalesce, and leaves turn brown or yellow and die-back from the tip. When extended overcast weather conditions persist, stand density may deteriorate.	Cool, moist periods of spring and fall.
RHIZOCTONIA BROWN PATCH Initially, circular patches are 3" - 6"; increasing to 12" or greater. There may be a gray "smoke ring" on the perimeter of patches during early morning hours. Patches often coalesce during extended hot and humid weather. Leaves severely blighted; bearing oval to elongated, tan lesions with chocolate-brown margins. Disease is more severe under high nitrogen fertility or frequent irrigations, and often reduces stand density.	June-Sept., especially during hot, humid night conditions when heavy dew forms or during hot and rainy periods.
DOLLAR SPOT Roughly circular spots 3-6" in diameter. Leaves dying-back from the tips. Lesions somewhat oblong, white in color with a brown border where green and white tissues meet. Foliar mycelium may be evident during early morning hours when there is a heavy dew.	May - Sept., especially during periods when days are warm, but nights are cool.

Mimeo prepared by Peter H. Dernoeden, Extension Turf Specialist