Necrotic ring spot on Kentucky bluegrass

Necrotic ring spot disease is one of many that can affect lawns. This disease is difficult to control and the most common lawn problem in Colorado. The disease causes rings of dead grass, about one foot in diameter, in a lawn. It's caused by a fungus, but no mushrooms are associated with the ring.

The best control is preventative practices, such as rototilling soil and adding organic material before sodding. The fungus responsible for necrotic ring spot lives in the soil. Adding organic material to the soil helps grass maintain a healthy root system, helping it ward off disease on its own.

Necrotic ring spot disease can be managed by core aerating the lawn at least once a year to slowly improve soil conditions and root growth. Avoid over fertilizing and frequent, light watering. It is better to water the grass infrequently and deeply, forcing the grass roots to develop to a depth of six to eight inches. Mowing heights should be maintained at approximately two and one-half to three inches.

Since the disease is so difficult to manage, alternative grass choices should be considered. Perennial ryegrass is not susceptible to this disease and is commonly used to overseed affected areas. There are also some Kentucky bluegrass varieties such as Midnight and Eclipse that are resistant.

 

 

Fairy Ring in Turfgrass

by L.P. Pottorff ¹

Quick Facts...

• Fairy ring is caused by a number of mushroom fungi that live in the soil and thatch layer.
• Early symptoms of infection appear as circular or partial ring-bands of stimulated grass that vary from less than 1 foot to many feet in diameter.
• To control an established fairy ring, aerate the entire diseased area every 4 inches plus an additional 2 feet.
• Areas of dark green grass often can be masked with light applications of nitrogen fertilizers that stimulate adjacent turf growth.

Fairy ring is a common disease of Kentucky bluegrass and most other turfgrass species. It is caused by many mushroom fungi that live in the soil and thatch layer. Damage often is unsightly and sometimes a serious problem even on well-maintained lawns. Fairy rings develop over a wide range of fertility levels and soil and climatic conditions. The disease tends to be worse on lawns maintained at low soil moisture and fertility levels.

Figure 1: Fairy ring.

Symptoms

Early symptoms of infection appear as circular or partial ring-bands of lush green grass that vary from less than 1 foot to many feet in diameter. Most rings range from 3 to 12 feet. Eventually the deep green grass in the ring-band dies. This pattern of stimulated and dead grass (Figure 1) may be visible throughout the year and may slowly increase in size during following seasons. Mushrooms or puffballs of the fungus may appear in the rings following periods of wet weather.

Disease Cycle

How fairy rings begin is unknown. Fungi that cause fairy rings commonly live in forest areas. It is thought that they begin to grow on a source of organic matter such as an old stump, dead roots, or wood left over from building construction that was buried during the landscaping process. The fungi grow radially outward in the soil or thatch layer of the turfgrass. Fungi that cause fairy ring live by decomposing organic litter that is abundant in the turfgrass thatch. The lushness of the stimulated zone occurs because the fungi release nitrogen as they decompose the organic matter in the thatch and soil.

The dead zone contains grass plants that may be killed or dormant, mostly as a result of insufficient soil moisture. This ring of drought-stressed plants occurs because of an extensive network of mycelium or dense mold produced by the fungus. This mycelial layer prevents water from infiltrating into the soil and reaching turf roots.

 

 

SNOW MOLD BEST BATTLED BY RAKING, NOT FUNGICIDE, ACCORDING TO COLORADO STATE UNIVERSITY TURF SPECIALIST

FORT COLLINS - Many Front Range lawns are now being afflicted with gray snow mold, caused by a fungus called "Typhula incarnate." Snow mold most often occurs during periods of prolonged snow cover, but can also occur where leaves and other debris has accumulated on lawns during the fall and winter, said Tony Koski, a turf specialist with Colorado State University Cooperative Extension Agency.

North-facing lawns, shaded lawns, and areas where snowplowing or drifting snow created especially deep snow will be the most commonly affected parts of the landscape. The fungus is most active in moist lawns at temperatures just above freezing. Circular patches (6-12 inches across) will have a moldy appearance if the fungus is actively growing - usually just as the snow melts and the lawn is exposed.

As the lawn begins to dry out and fungal growth slows, the patches can take on a light tan appearance, fading to light gray or white. Under severe conditions, these smaller patches may grow together to form large, matted areas that appear to be dead. This disease rarely kills turf in the home lawn, although young seedlings from a late fall seeding may be killed (fall sod will be alright).

"Fungicide applications are not recommended when snow mold occurs in a home lawn," Koski said. "Spring fungicide applications will not effectively control or prevent the disease, nor will fungicide use hasten spring turf recovery."

The best way to speed recovery is to remove dead and matted material by light raking to promote air circulation and drying. Light spring nitrogen fertilization (especially if no fertilizer was applied the previous fall) will help speed the formation and growth of new grass from the underground stems that are not harmed by the snow mold fungus. Lawns that appear slow to recover this spring will benefit from core cultivation, followed by overseeding with the same grass species already present in the lawn.

"Contrary to popular belief, late-season fertilization -- also referred to as 'winterizer' -- neither encourages snow mold, nor increases its severity," Koski said. "In fact, late-season/fall fertilization will encourage more rapid healing and recovery when lawns are afflicted with snow mold."

Koski said gray snow mold is generally uncommon in Front Range lawns because snow must continuously cover the lawn for at least 40-60 days before the fungus becomes noticeably active - a rare occurrence on Front Range lawns.

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