Red Thread

Red Thread caused by the fungus Laetisaria fuciformis, is favored by cool, humid weather. Red Thread may become more common on lawns with fescue and ryegrass blends. Red Thread causes the lawn to have a bleached patchy appearance. Irregular areas, from several inches to several feet across, develop a whitish to pinkish color. Leaf blades and sheaths are attacked; at first they develop water-soaked or greasy green areas, then the affected parts dry out and become tan-colored. In wet weather the affected leaves are covered with a gelatinous pink fungus which then forms bright red threadlike strands near the tips of the leaves and from leaf to leaf.

The best temperatures for Red Thread development are 68-75 F. Red Thread can be quite severe on red fescue (a component of many shade-tolerant lawn grass mixtures) and may occasionally be severe on bluegrass.

Fusarium Patch (Formerly Pink Snow Mold)

The Fusarium Patch fungus, Microdochium nivalis, produces yellowish patches from several inches to a foot in diameter which usually appear as soon as the snow begins to melt and continue to enlarge as long as the weather is cool and the grass wet. The patches soon take on a bleached appearance. When the grass remains wet, it may be covered by a mat of cottony mold which is off-white or faint pink. This pink color and the absence of sclerotia distinguish Fusarium Patch from Typhula Blight. Usually only the leaves of Kentucky bluegrass are killed but entire plants may be killed in years of severe snow mold activity.

Fusarium Patch develops under a snow cover on unfrozen ground and also can develop in cool wet weather in fall and spring as long as the temperature is between 32 and 60 F.

The two snow mold diseases do not occur every year on lawns, but are most apt to occur in a year when an early and deep snow cover prevents the ground from freezing. A cold open winter will not promote snow mold on lawns but may cause winter injury, with patches of grass dying because the crowns were killed by freezing and/or drying (desiccation).

Proper lawn management will reduce the danger of snow molds. Management practices include keeping the lawn mowed in the fall so that there is no thick mat of grass for the snow molds to develop on. Lawn areas where snow molds occur should not be heavily fertilized in late summer or early fall. A late fall application of fertilizer (after October 15) will not promote lush growth and snow mold. Snow molds do not occur often enough on lawns to merit a fall application of fungicide as a preventive measure unless there is a history of snow mold. When snow mold is observed in the spring it is usually too late to apply fungicide. Typhula Blight normally continues development for only a few days after the snow is gone. Fusarium Patch can develop longer, following snow melt, especially when cold rain or late spring snow is expected. The application of a fungicide might prevent additional damage from Fusarium Patch but is seldom recommended. Usually light raking with a leaf rake will improve air movement and aid lawn recovery. If recovery does not occur, affected areas may need reseeding.

Mushrooms

Various mushrooms may appear in lawns, but not injure the grass. However, they may be unsightly and cause people to worry that children or pets may eat them. Some lawn mushrooms are poisonous to very poisonous, others are not poisonous There is no way to distinguish poisonous from non-poisonous except by correct identification by a qualified expert.

There is no easy control for lawn mushrooms which appear whenever there is a protracted rainy period. These mushrooms grow on organic matter (including thatch) and decaying wood. Where possible, the removal of buried wooden scraps and old stumps will reduce greatly their food source and the number of mushrooms in future years. Mushrooms that do appear can be raked up and destroyed, minimizing danger to children or pets.

Slime Molds occasionally form on grass during periods of prolonged rainfall and high humidity. A creamy white slimy substance accumulates on the grass (Figure 16). Later, this slimy substance becomes powdery and white, gray or blue-gray. Slime Molds do not cause any direct damage to the grass because they only grow over the surface of the leaf and do not attack it. However, they may cause some injury if they remain on the grass for a long period of time. The exclusion of light may cause a yellowing and weakening of the grass, making it more easily attacked by other organisms. The simplest control of Slime Molds is to brush them off the grass with a broom or rake.

Moss and Algae

Moss and algae are primitive green plants often found in densely shaded and moist lawn areas and sometimes on landscape materials and buildings. The best control involves improving soil drainage, increasing air circulation and light intensity, and planting shade-tolerant ground covers or turfgrass varieties. Chemical controls for algae are available but are only a temporary solution and may cause injury to adjacent vegetation.

Dog Damage

Grass may be injured by dog urine. The spots resemble Dollar Spot or Rhizoctonia Blight. The difference is that outside the area of dead grass there is often a zone of grass with luxuriant growth. Heavy watering will wash down excess salts and may help the grass recover.

Sclerotinia Dollar Spot

Dollar Spot, caused by the fungi Lanzia spp. and Moellerodiscus spp., produces 4-6 inch circular to blotchy areas on bluegrass lawns. These patches are straw colored. Early in the morning, when the grass is covered with dew, a faint cobwebby growth may be seen on the leaves of affected plants. In the early stages of disease, leaves develop distinct tan-colored spots and bands; quite often a reddish-brown border can be seen on the leaf spots.

Dollar Spot develops at temperatures of 60-85 degrees Fahrenheit with high humidity and low soil moisture. The disease usually develops on lawns which are unfertilized but occasionally occurs on high maintenance lawns under stress. It can be controlled by keeping lawns adequately fertilized and watered and by using a fungicide as necessary. Bluegrass varieties differ in Dollar Spot susceptibility with most being moderately susceptible or moderately resistant.

Summer Patch

Summer Patch, caused by the fungus Magnaporthe poae, may be destructive on bluegrass and fine leaved fescues. It is a disease that occurs during the hot portion of the summer. The initial symptoms are yellow patches 6-12 inches in diameter. The turf in these patches thins and the remaining turf turns bronze in color. If warm weather continues, all of the turf in the patch may die. The dead patches may be colonized by weedy grasses.

Soil moisture is important in disease development. Excess irrigation or an absence of irrigation during hot weather may make the disease more severe. Heat stress and drought stress can intensify disease symptoms. Avoid low mower cutting heights during periods of heat stress.

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