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Fungus
-FUSARIUM BLIGHT OR NECROTIC RING SPOT-
Identification: When first infected by Fusarium Blight, patches of grass from 2 to 6 inches in diameter turn light green. While these areas can be circular in shape, they can also appear as elongated streaks or even crescents. During periods of high temperatures, the areas affected by the disease quickly change color from there initial light green to a reddish brown and, finally, to a tan or straw-colored appearance. During this time, the most obvious symptom to show that it is, in fact, Fusarium is the appearance of a roughly ring-shaped area up to 3 feet in diameter that contains a patch of healthy grass in the center. This gives the affected area a "frog-eye" pattern. As the disease continues and the grass dies, the crown and basal area of the dead grass displays a reddish rot and becomes hard and tough. On an individual level, dark green blotches envelope the full width of the leaf blade and, eventually, these blotches become reddish-brown and then a dull tan.
Cause: While this disease is actually caused by a fungal growth, there are several conditions which favor its appearance and growth. When daytime temperatures reach 70 degrees or higher, this fungus begins to produce spores. As temperatures become 75-90 degrees and there is high humidity, the spore production increases dramatically and can kill infected areas in as little time as 4 to 7 days after the first symptoms appear. When temperatures and/or humidity is low, however, the disease shows very little activity. High nitrogen levels, excess thatch, and excessive watering can also contribute to the appearance and spread of this disease.
Prevention:
- Remove excess thatch
- Maintain a regular watering schedule, avoiding frequent, shallow waterings
- Fertilize your lawn appropriately
- If you are planning on seeding bluegrass, it is recommended that you add a mixture of 20% perennial ryegrass as well to help prevent this disease
- Maintain your lawn at the recommended height
Treatment: The only way to treat this disease, beyond stricter maintenance controls or reseeding to repair damage, is to apply fungicides. It is recommended that, if you choose to use a fungicide, that you apply it during the spring before or just after symptoms of Fusarium Blight appear.
-FAIRY RING-
The name fairy ring comes from an old folk-tale. People once believed that mushrooms growing in a circle followed the path made by fairies dancing in a ring. Fairy rings are found in open grassy places and in forests.
In grass, the best known fairy ring fungus has the scientific name Marasmius oreades. The body of this fungus, its mycelium, is underground. It grows outward in a circle. As it grows, the mycelium uses up all of the nutrients in the soil, starving the grass. This is the reason a fairy ring has dead grass over the growing edge of the mycelium. Umbrella-shaped fruiting bodies, called mushrooms, spring up from just behind the outer edge of the mycelium.
Large rings are created when the older mycelium in the center finally exhausts the soil nutrients and dies. On the death of the central mycelium, the nutrients are returned to the soil and grass can grow again.
The living edge of the mycelium continues to grow outward. As it grows, it secretes chemicals into the ground ahead. These chemicals break down the organic matter, releasing nutrients so that the mycelium will have food when it reaches this area. For a brief time, the grass at the outer edge of the ring also benefits. The extra nutrients make the grass darker green, taller, and thicker than the rest of the lawn or pasture. This lush grass dies when the mycelium grows under it and steals the nutrients.
Fairy rings made by fungi like Marasmius oreades are called “free” rings. They will continue to grow outward until a barrier is reached. Sometimes the barrier is another fairy ring! Rings can grow into each other’s territory and die as each reaches the other’s “dead zone.”
If there are no barriers, free rings can grow outward at up to 8 inches (20 cm) per year. They can reach a diameter of over 30 feet (10 m). One ring formed in France by the fungus Clitocybe geotropa is almost a half mile (600 m) in diameter. This ring is thought to be 700 years old.
Mycorrhizal fungi, which live in symbiotic partnership with trees, also form fairy rings. Their rings are called “tethered” rings. A tether is like a leash. The fungus and its mycorrhizal partner tree need each other to survive. The mycelium of these fungi always remains joined to the tree’s roots. Roots are the “tether” that keeps the fairy rings of mycorrhizal fungi from growing too far from their tree.
-LEAF SPOT-
Leaf Spot is common and very destructive to Kentucky bluegrass. It is most damaging when the weather is cool and moist during the spring and fall. Grass blades have small oval spots with straw colored centers and maroon borders. Infected areas turn yellow and die. The lawn appears to be under-watered and under-fertilized, but don’t be fooled.
What will happen to my lawn? In addition to damaging the leaf blades, the fungus can attack the crown and roots of grass plants. This usually occurs in the spring and early summer, and can cause extensive dieback of the grass. Left untreated, the plants can die in large, irregular patches several inches up to many feet in size. This may produce an irregular patchwork of damage across an entire lawn requiring multiple treatments of fungicide to get the disease under control. Combating Leaf Spot can be a timely and unpleasant weekend activity.
What can I do? Make sure you bag your grass clippings to prevent the spread of this disease until lawn has recovered. Avoid overwatering. Do not water the lawn in the late afternoon or evening. Provide good soil drainage. Do not allow thatch levels to accumulate. Sometimes a fungicide is necessary to achieve complete control. Some local hardware stores carry fungicides that can treat Leaf Spot. Be sure to read the label and apply according to the directions. Depending on the severity of the disease, more than one fungicide application may be required.
-MELTING OUT-
Irregularly-shaped dead patches in your lawn could be from a fungal disease called melting-out. Melting-out is one phase manifested by the leaf, crown and root rots that are the most common and serious group of diseases attacking lawn and turf grasses in the US.
When the fungi attack the leaf portions of grass, the symptoms are small dark brown, reddish-brown, or purplish spots which appear on the grass blades from early spring to late fall. The spots increase rapidly in size, become round or oblong, and the centers gradual fade to an ash white or straw color. Sometimes, the spots are described as “eye-spots”. Leaf infections are sometimes so severe that the blade is girdled and drops, sometimes entire grass plants are killed.
These fungi can be very destructive during wet, humid weather or in areas where the turf is sprinkled frequently, especially in late afternoon and early evening. The more often grass is wet and the longer it remains wet, the greater will be the chance of disease.
With the arrival of relatively dry weather, the fungi may attack the roots of diseased plants. These symptoms usually appear first in warm to hot weather as a reddish-brown decay of the root tissues. Sometimes the color turns chocolate-brown to black. Such plants lack vigor and often wilt during mid-day, even when soil moisture is abundant. The lawn may have a drouth-injured appearance, then gradually turn brown and begin thinning out. As the disease progresses, large irregular areas are yellowed, then become straw-colored and die out. This is called the melting-out phase. In some instances the entire lawn can be lost. Once the fungi that cause melting out disease become established in a lawn they cannot be eradicated and remain an ever-present problem.
To manage melting-out disease, mow bluegrasses, fescues, and ryegrasses at the recommended maximum height. Avoid close clipping at all times. Mow the grass so that no more than 1/3 of the grass height is removed at one time.
If dense thatch more than one-half inch thick has formed, reduce or remove it with a power rake in the spring or early fall. These machines can be rented at most large garden supply centers. Application of sufficient, but not heavy amounts of slow-release available nitrogen can also help. Too much nitrogen can be detrimental and can leach into the ground water. Soil tests can determine proper amounts. Proper watering practices will also help manage melting-out disease.
-RED THREAD-
Red Thread lawn fungus appears in turf as small pinkish-red spots or patches, usually in later May and June when temps are high, and humidity is higher. Infected areas eventually turn light tan, and the leaf tips or margins may be covered with fine pink to red threads, giving the turf an overall pink coloration.
Red Thread, also known as "Pink Patch,"occurs in the cooler and more humid areas of the Pacific Northwest, Northeast, and Midwest. It is most severe on slow growing, nitrogen- deficient turfgrass during damp weather.
-SNOW MOLD-
Snow mold is a fungal disease that appears in early spring as the snow melts. There are two types of snow molds, gray and pink, that become active under the snow cover. Gray snow mold (also called Typhula blight) is caused by Typhula spp., while pink snow mold (also called Fusarium patch) is caused by Microdochium nivalis.
Gray snow mold survives hot summer temperatures in the soil or in infected plant debris as sclerotia, resistant fungal structures, while pink snow mold survives as mycelium or spores in infected plant debris. Fungal growth begins in the winter, beneath a cover of snow on unfrozen ground. Growth can take place at temperatures slightly below freezing and may continue after snow melt, as long as the grass remains cool and wet. Gray snow mold activity stops when the temperature exceeds 45° F or the surface dries. Pink snow mold activity may continue during wet weather in the fall and spring, as long as the temperature is between 32° F and 60° F.
Symptoms first appear in the lawn as circular, straw colored patches when the snow melts in the spring. These patches continue to enlarge as long as the grass remains cold and wet. Grass within the patch often has a matted appearance and colored fungal growth. The fungal growth may cover the entire patch or develop along the margins, with gray snow mold being white to gray in color and pink snow mold being white to pink in color. Occasionally, fungal fruiting bodies (mushrooms) may be seen emerging from infected turf. Hard structures, called sclerotia, may also develop on the leaves and crowns of plants infected by gray snow mold, not pink. The sclerotia are spherical in shape and roughly the size of a pinhead. Their presence helps to distinguish gray snow mold from pink snow mold.
Snow molds do not occur in the home lawn every year, but are most common during years when an early, deep snow cover prevents the ground from freezing. A cold, open winter will not promote snow mold, but may cause winter injury. The damage caused by snow molds is seldom serious. Generally, infected areas are just a little slower to green up. Gently rake affected areas of the lawn to promote drying and prevent further fungal growth. Fungicides are not usually recommended, but in severe cases a preventative spray of thiophanate-methyl (Cleary’s 3336) in October or November may be helpful.
The following steps can be taken to minimize damage in future years:
- Avoid excessive applications of nitrogen fertilizer in the fall.
- Continue to mow the lawn at the recommended height until it is no longer actively growing. The taller the grass, the more likely it will mat down and encourage snow mold development.
- Rake up leaves in the fall.
- Manage the thatch layer to avoid accumulations of more than ½ inch.
- Spread out large snow piles to encourage rapid melting. Use snow fencing to minimize snow accumulation in problem spots.
