Common Lawn Diseases

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Lawn diseases are generally fungus infections of your grass plants. The fungus spores normally occur in the soil and become a problem for home lawns when conditions for their excessive growth are right. The weather components of moisture, sunlight and temperature can come together with the lawn site to make conditions for disease to spread. The lawn site factors that effect disease spread are exposure to sunlight, wind and mirco-relief.

These more common lawn diseases are divided into two groups. First, diseases of the leaf blade, where the blades are affected and can be re-grown after the disease has moved on when conditions for spread are not optimum. Generally, these diseases are not detected until after the fact. Second, are the diseases that affect the crowns of the grass plant. These diseases are very destructive and must be quickly controlled before the disease kills the entire lawn. The dead grass plants can only be replaced by seeding. Preventative fungicide treatments are not recommended because they are very expensive and the combination of weather and site factors are hard to predict.

RED THREAD (a leaf blade disease):
Susceptible Grasses Include: Bluegrass, Ryegrass, and Fescue
Conditions Favoring Disease Development: Periods of cool, wet weather when leaves are wet from dew, fog or frequent light watering. It develops best when the grass is growing slowly due to cold weather or pest related stresses.
Symptoms of the Disease: Circular shaped patches appear and die rapidly during cool, wet weather, Reddish-pink colored fungal strands can often be seen binding leaf blades together. When dry the strands resemble red threads.
Cultural Practices to Follow: Cultural Practices to Follow Avoid evening watering. Collect clippings to reduce spread of the disease. Collect clippings and wash mower after use until the disease has
been controlled.

RUST (a leaf blade disease):
Susceptible Grasses Include: Ryegrasses, some bluegrasses and some fescues.
Conditions Favoring Disease Development: Moderately warm and humid weather and lawns stressed from lack of water, fertility and improper mowing. Most often found on newly seeded lawns where the rapidly growing young grass plants demand more nutrients than are available. Generally occurs in the late Summer.
Symptoms of the Disease: Small yellow/orange fleck on the leaf blades. Fleck enlarges to form rust-colored pustules. Leaf blades yellow, wither and dieback. Over all lawn may turn yellow-orange to reddish-brown.
Cultural Practices to Follow: Reduce stressful conditions. Maintain or improve soil moisture levels through summer. Water correctly (deeply and at long intervals of a week to a week and a half). Fertilize sparingly with adequate amounts of phosphorus and potassium to increase soil fertility. Mow properly in the afternoon after the heat of the day has passed. Collect clippings and wash mower after use until the disease has been controlled

BROWN PATCH: (a leaf blade disease):
Susceptible Grasses Include: Tall Fescue, Bluegrass and Ryegrass.
Conditions Favoring Disease: Excessive thatch layer (greater than 3/4th of an inch), high humidity and periods when the leaf blades remain wet for a long time (two or more days), hot weather of 75 to 90 degrees during the day and above 60 degrees at night and soft lush growth.
Symptoms of the Disease: Affected leaf blades first appear water soaked and dark. Leaf blades then wilt and become light brown as tissue dies. A leaf lesion may appear irregular in shape, tan in the center and dark brown borders. Symptoms on high cut grass may resemble a ring with centrally located tufts of healthy grass observed within the patch.
Cultural Practices to Follow: Minimize environmental stress to turf and remove excess thatch and improve root development by core aeration. Fertilize sparingly and insure adequate amounts of phosphorus and potassium. Avoid evening watering. Trim trees and shrubs to allow for better air movement and light penetration.

DOLLAR SPOT ( a leaf blade disease):
Susceptible Grasses Include: Bluegrass, Ryegrass, Fescue and Zoysia Grass.
Conditions Favoring Disease Development: Warm, moist weather when heavy dew occurs. Plants growing in dry soils with high moisture levels around the leaves from dew and frequent watering. Leaf clippings and foot traffic can spread this disease.
Symptoms of the Disease Infected leaf blades have light tan lesions with reddish-brown borders. Lesions take on an hourglass shape. Small spots occur in the lawn about two inches or less in size, but left unchecked may grow together to produce large irregular brown areas. Cobweb like threads of mycelium can be seen when grass is wet with dew.
Cultural Practices to Follow: Remove excess thatch (more than ½ inch or more.) and improve root development by core aeration. Water in the morning, so the leaf blades can dry quickly. Water correctly (deeply and at long intervals of a week to a week and a half) to prevent prolonged leaf wetness. Stay off lawn when wet. Foot traffic can spread this disease. Fertilize sparingly with addition nitrogen if lawn has not received fertilization within the last four week.

LEAFSPOT: (a leaf blade and crown disease)
Susceptible Grasses Include: Ryegrass, Bluegrass and Fescue
Conditions Favoring Disease: Disease can occur over a wide range of temperatures, ranging from 50 to 90 degrees, accompanied by high humidity. Grass plants grown under stressful conditions along with the presence of a heavy thatch (greater than 3/4th of an inch) tend to be most susceptible.
Symptoms of the Disease: Affected leaf blades have characteristic dark circular or oval shaped lesions that have the appearance of a cigarette burn. As the disease infects the plant, the crown and root areas become damaged causing the plants to thin or "melt out". Areas of the lawn will yellow and eventually thin and die if the disease is severe. Certain varieties of ryegrass can literally die out overnight when the "melting out" phase of the disease is reached.
Cultural Practices to Follow: Water correctly (deeply and at long intervals of a week to a week and a half) to prevent prolonged leaf wetness. Water in the morning, so the leaf blades can dry quickly . Prune trees and shrubs to allow for better light penetration. Remove excess thatch and improve root development by core aeration. Avoid continual close mowing and keep mower blades sharp to reduce the area of open wounds in which the disease can spread. Avoid excessive nitrogen fertilization during the cool, wet periods of spring.

NECROTIC RING SPOT: (a crown disease)
Susceptible Grasses Include: Bluegrass, Ryegrass and Fescue.
Conditions Favoring Disease: This disease begins to invade turf during periods of cool, wet weather. Infection takes place during the months of March, April and May with some activity in the fall month of October and November. Dense turf with a heavy thatch layer tends to be more susceptible to infection.
Symptoms of the Disease Large circular patches of straw colored plants measuring up to 12 inches in diameter. These patches take on a characteristic donut or "frog-eye" appearance with apparent healthy grass in the middle. As the infection spreads these patches tend to join together causing large pock marked areas. Damage from this disease will be most evident during the summer months when the lawn becomes stressed by ho, dry weather conditions
Cultural Practices to Follow: Minimize environmental stress to the lawn by mowing your lawn at three inches. Frequent light watering helps to cool the grass plants and provides moisture to the shortened root systems of the infected plants. Since the disease tends to occur in lawns with heavy thatch layers, a program o thatch modification or removal must be incorporated into your lawn management program. Start scheduling two aerations (spring and fall) to slowly reduce thatch thickness.

PYTHIUM BLIGHT: (a crown disease)
Susceptible Grasses Include: Bluegrass, Ryegrass and Fescue
Conditions Favoring Disease: Cloudy days with high temperatures and humidity and poor air circulation can favor this disease. When the night time temperatures exceed 80 degrees and the humidity is greater than 65% for two or more days in a row, this disease can run through a lush, thick lawn quickly. Soils with a pH level of greater than 7.0 or more are susceptible. This disease can be tracked by surface drainage water.
Symptoms of the Disease Starts as small "grease" spots that fade to straw colored areas. Bases of the grass plants feel and appear to be "greasy". Spots merge to become larger patches of dead matted grass. White cobwebby mycelium maybe found in the early morning on these patches. In newly seeded lawns this disease may cause "damping off" and kill the young plants. Some straw colored lesions may be found on the edges of the patches.
Cultural Practices to Follow: Improve drainage, prune trees and shrubs to improve air circulation and reduce thatch thickness with aeration. Adding sulphur in the spring an fall may help also. This disease may have to be stopped with an application of a fungicide. Aeration and over-seeding with improved varieties of grass will help in repair of damaged areas after the conditions for the disease have abated. Often sunny weather will break the disease cycle.
Most diseases of turfgrass are caused by simple mirco-organisms.