Turf Problems to Watch for This Spring
As the weather warms this spring and turf begins actively growing, pathogens will also become active in infected tissue. The most common turf diseases in Utah are snow molds, necrotic ring spot, and take-all patch.
Snow molds, both gray snow mold (Typhula spp.) and pink snow mold (Microdochium nivale), first appear after snow melt. These fungi are different than most because they thrive in cooler temperatures. Infection begins under snow cover and disease symptoms in the turf are not visible until the snow begins to melt. These diseases can occur separately or together and almost all turf species are susceptible to both.
Pink snow mold first appears as circular patches of infected turf that can change color from orange-brown to dark reddish-brown to light gray or tan. There may also be a faint growth of white or light pink mycelium around the edges of the patch, but the pink color is only noticeable at certain times of the day. If the conditions are cool and wet for a prolonged period of time, the patches can combine, creating larger areas of infected turf. Numerous, small clusters of pink spores are produced on the surface of the leaves. The spores begin new infections as they move to other areas of the turf. The symptoms can be confused with gray snow mold.
The first symptoms of gray snow mold are areas of yellow, straw-colored turf. The leaves become matted and covered with a thick or thin layer of white to gray mycelium. The mycelium eventually dries, giving the leaves a gray or silver color. Infected leaves will be covered with small, black sclerotia, which the fungus uses as overwintering structures. Infected patches can coalesce into larger areas when conditions are favorable. Gray snow mold is different than the other diseases in that only the leaves are killed while the crown is not affected. So new leaves will be produced from the crown.
Necrotic Ring Spot
Although necrotic ring spot (Ophiosphaerella korrae) develops during cool, wet weather, symptoms may not be noticeable until the turf is drought stressed in the summer. The first symptoms are small, light green areas of turf. As the leaves are infected, they will turn a reddish-brown to bronze color, weakening to a light straw color. The turf will frequently survive or re-colonize the center of the patch giving it a ring-like appearance known as a “frog-eye.” In some cases, all the turf in the patch will die resulting in a sunken depression. There are no leaf lesions present on the foliage of infected turf. As the disease advances, roots, crowns, and lower stems will develop a black or brown color due to the presence of fungal hyphae. Infected roots may become severely rotted. This disease is typically more severe in turf established from sod and in areas with compacted soil. Symptoms will usually appear two to three years after the turf is established.
Management practices that reduce stress on the turf will also help suppress necrotic ring spot. Water lawns deeply and as infrequently as possible. However, if your turf is infected with necrotic ring spot, frequent watering will cool the grass and allow plants with depleted root systems to survive the late afternoon heat. In this case, light applications of water can be applied daily to infected turf to reduce heat stress and begin recovery. Core-aerate, with clean equipment, and maintain a balanced fertilization program, especially for nitrogen, phosphorus, and potassium. Slow-release fertilizers, rather than quick-release forms, will reduce disease severity.
Symptoms of take-all (Gaeumannomyces graminis) appear in late spring or early summer and persist through the summer, becoming more noticeable when the turf becomes stressed in hot, dry weather. Infected turf can have symptoms similar to necrotic ring spot or pink snow mold. They begin as small light brown or reddish-brown patches. The edges of these patches or the whole patch can be reddish-brown or bronze when the disease is actively developing. The roots will have dark brown streaks and as the disease progresses the stolons, rhizomes, roots, and shoot bases will turn dark brown or black. The plants will become brittle in hot dry weather and pieces can be easily pulled from the soil.
-Erin Frank, Plant Disease Diagnostician