| Several fungal diseases attack lawn grasses.
Following is a short description of the most common
diseases to help you sort out which one may be
causing your problem. The diseases have been
categorized as patches (cause dead spots or patches
in the lawn), rings (cause rings of dead or affected
grass), or leaf blight (affect individual blades of
grass, often over a wide area and no distinct patch
or ring pattern may be noticeable). Since most grass
diseases affect leaves, patches and rings describe
certain diseases in more advanced stages
of development.
Result in Dead Spots or Patches
BROWN PATCH (Rhizoctonia solani) Round patches
of turf up to several feet in diameter appear watersoaked
and eventually turn brown. Dark gray smoke
ring is sometimes visible on lower mowed turf.
DOLLAR SPOT (Moellerodiscus spp. & Lanzia spp.
or Sclerotinia homeocarpa) Rounded, straw-colored,
slightly sunken patches up to 2 inches in diameter
on bentgrass greens, 4–6 inches in diameter on
other lawns. Spots have a reddish margin and
expand until they girdle the leaf blade. Cottony
mycelium may be evident in the morning growing
over dead tissue.
RED THREAD (Laetisaria fuciformis) Pinkish patches
from 3 to 15 inches in diameter develop during
rainy weather. The grass in the patches is pink and
dead and contains coral-red masses of mycelium.
The disease is more common in fescues and grows
best from 60 to 70 degrees F.
SNOW MOLD (Gerlachia nivalis and Typhula spp.)
Grayish white patches up to 3 feet in diameter.
Grass blades are collapsed and matted. Several
different fungi are responsible for snow mold
disease. Dead areas appear in the turf after the snow
has melted.
PYTHIUM (Pythium spp.) Rounded sunken patches
up to 1 foot in diameter. Leaves appear water-soaked
and shiny at first, turning tan when dry. White
mycelium grows over all leaf tissue, not just dead
tissue as in dollar spot.
Result in a Ring in the Lawn
FAIRY RING (Marasmius oreades and others) Dark
green ring with lighter green center, 2 ft to 100 ft in
diameter. A mycelium starts in one spot and spreads
in all directions. At certain times of the year, the
fruiting bodies, mushrooms, may develop near the
outer borders of the year’s growth of mycelium. The
grass within the ring may appear to be healthy but
later may collapse and die.
NECROTIC RING SPOT (Leptosphaeria korrae) 1–3
patches of red or purple leaves that bleach with
water stress. Many patches grow greater than 12
inches in diameter with weeds or resistant grasses
forming frog-eyes in the center of the ring.
SUMMER PATCH (Magnaporthe poae) Small tan or
straw-colored spots appear on the leaves in early
summer. These spots enlarge and coalesce until
large areas of the lawn are killed. This disease is
active only during the warmest part of the summer.
Affects Scattered Leaves
POWDERY MILDEW (Erysiphe graminis) Powdery
mildew appears as dirty spots or blotches on the leaf
sheaths, varying in color from light gray to brownish.
It is especially prone to develop in wet weather and
on poorly drained lawns. The infection spreads by
the numerous white spores, which form on infected
leaves.
LEAF SPOTS (also called Melting out, various
organisms) Many grasses are affected by leaf spot
diseases. General symptoms include tan or strawcolored
spots on leaves usually bordered by a darker
color. Black spore-producing structures may be seen
in the center of the spots of some diseases.
RUST (Puccinia graminis var. agrostis) The disease
appears as small, reddish spots on the leaves.
Merion bluegrass, a special strain of Kentucky
bluegrass, is very susceptible to this disease.
ANTHRACNOSE (Colletotrichum graminicola). This
disease is common on creeping bentgrass and
annual bluegrass. The fungus causes individual grass
blades and/or plants to yellow and die when it
invades crown and root tissue. Black, hairy, and
spiny fruiting bodies are abundantly produced on
dead tissue but may also be seen on green leaves
as well. | 
