Patch diseases will occasionally occur in bluegrass lawns. Areas of turf die in patches, hence the name. Advanced stages of the disease appear as rings of dead turf surrounding living turf that resembles a "frog's eye". Researchers have identified several fungi that cause patch-like symptoms. Some of the more common patches include summer patch, yellow patch and necrotic ring spot.

Necrotic ring spot and yellow patch are active during cool weather in the spring and the fall, but patches may remain into the summer months. Summer patch is active during the summer period. Once established, these diseases are extremely difficult to control, and tend to occur in following years.

Red thread and pink patch are diseases that attack Kentucky bluegrass, fescues, rye grass, and bent grass. These diseases are active during the cool, moist periods of the year, causing distinct-to-irregular discolored patches to develop in lawns.

The leaves often become covered with a pink, fibrous growth. In the final stage, reddish fungal threads are found at the leaf tips. In a lawn infested with red thread or pink patch, pink areas from two to fifteen inches in diameter become readily apparent.

These spots may join to form large areas of damaged turf. Areas may turn brown and dry out. These diseases are most common under the combination of prolonged periods of high humidity, temperatures between 60?F to 75?F, and slow-growing, nitrogen-deficient turf.

To control red thread and pink patch, Mow and water correctly Maintain a sound fertilization program. For persistent problems, the lawn can be over-seeded with a more resistant turf grass variety or species. If detected soon enough, fungicides can be applied for temporary control of the disease. Patch diseases can be very damaging to most cool-season turf grasses. These diseases cause circular patches of dead turf, which may surround turf that is still green. This "frog eye" symptom often occurs with this group of diseases.

Patch diseases generally occur on sodded lawns, especially within the first 5 years of establishment. However, older lawns either established from seed or sod can also develop patch diseases.

Several fungi cause patch diseases. The actual fungal pathogen will depend on the specific patch disease. The more commonly occurring patch disease includes the following Necrotic Ring Spot (Leptosphaeria Patch) - Leptosphaeria korrae. Summer Patch - Magnaporthe poae. Yellow Patch - Rhizoctonia cerealis. These diseases can occur on several turf grasses, but are more damaging to Kentucky Bluegrass. In the past, some of these diseases may have been referred to as Fusarium Blight, but today are referred to by their current names. Initial symptoms appear as small spots (2 - 4" diameter) of light green turf. Spots enlarge to form light straw colored circles, irregular patches, and crescent patterns that are 1-2 feet in diameter.

Centers of the patches may contain grass that is alive or dead. When dead, the patches of grass appear crater like or sunken. Patches may overlap to form large areas of blighted turf. Symptoms may also appear as diffused patterns of yellow or brown turf. Blackening of the infected crowns, rhizomes, and roots is also characteristic. Yellow patch on bent grass generally occurs as yellow rings that often recover.

Necrotic Ring Spot and Yellow Patch are favored by cool, wet conditions, occurring primarily in the spring and fall. Summer Patch is favored by hot, humid conditions and occurs in the summer.

Identifying these diseases is difficult because the symptoms of Necrotic Ring Spot and Yellow Patch are still present during the summer, when Summer Patch is active.

Control of patch diseases is very difficult, and often unsuccessful. Patch diseases are more damaging if the lawn is improperly mowed and watered. Properly maintaining the turf will reduce damage and help in control.

During turf establishment, good soil preparation and selection of quality sod or seed are preventative measures. Core aeration to assist in better turf grass rooting will help in preventing disease and aid in recovery. Renovation of the diseased turf often is necessary.