Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001569
11/12/99
Controlling Lawn Diseases
Helminthosporium Leaf spot or Melting-out
These diseases can occur at anytime during the growing
season. Leaf spot is a problem on fescue while
melting-out is more of a problem on Kentucky bluegrass.
Both diseases cause small, purple to black spots on the
leaves. The center of the spots can turn brown and die
while the spot margin remains dark colored.
Symptoms of the disease are the spots until the fungus
reaches the plant crown. The plants die when the crown
becomes infected causing the green to fade away. The lawn
becomes yellowed then brown.
Cultural controls include mowing the grass at 2 inches and
avoidance of spring fertilization. Provide moderate
nitrogen fertilization during the summer and do not water
in the evening or at night. Use resistant varieties.
Commonly available fungicides that may be used according
to label directions.
Lawn Ring(Patch) Diseases
Several diseases cause rings of dead grass with live
green grass in the center. These can occur in both cool
and hot, dry weather. Many other problems are similar in
appearance and are easily confused with ring diseases.
Managing moisture and fertility levels is an important
aspect in controlling these diseases.
Symptoms are round circles of dead grass with green grass
in the middle. Sometimes there are purple or red grass
blades around the margins of the spots.
When possible, water for 20 minutes each day around noon
to suppress the symptoms. Avoid moisture stress as
drought favors these diseases. Apply 1/2 pound of
nitrogen per 1000 square feet in June, July and August and
1 pound per 1000 square feet in September and November.
Make the November application after the grass has stopped
growing.
Homeowners may find it easier and less expensive to manage
the diseases through cultural practices rather than use
the fungicides.
Snow Mold
Snow molds are active during cool weather and are most
noticeable in the spring after the snow melts. The spots
of dead grass killed by snow mold are easily confused with
patches of dead bentgrass. A late season application
nitrogen, leading to a late flush of growth, may
predispose the lawn to attacks of snow mold.
Symptoms are patches of dead, gray to straw colored grass
in the spring. A gray or pink fungus may be seen growing
at the edges of the patches.
Chemical controls may not be practical for home lawns. Do
not apply fertilizer late in the season unless the grass
has gone dormant. Rake out the dead grass and reseed if
necessary.
Brown Patch
Brown patch is not so common as some other diseases. The
fungus that causes the disease can be found in most soils
and can live for years without a host plant.
Symptoms are brown patches of grass ranging from a few
inches to several feet in diameter. Infected leaves are
at first water-soaked but later dry and turn dark brown.
A "smoke ring" occurs around the outside of the patch when
the humidity is high. Brown patch has a slimy appearance
when it infects perennial ryegrass.
Avoid high nitrogen levels during hot, humid seasons
and remove the dew in early morning to reduce the disease
severity.
Dollar Spot
The dollar spot fungus is most active when the temperature
is between 70 and 90 degrees. The disease is
spread by infected clippings moved about by mowers, hoses
and shoes.
The symptoms are sunken, straw-colored spots about the
size of a quarter to a silver dollar. A fluffy, white
fungal growth may be seen in the spots in the early
morning while the grass is still covered with dew. The
lesions on blades of Kentucky bluegrass are yellowed to
bleached bands with reddish brown borders on the ends of
the lesions.
High nitrogen levels will reduce dollar spot.
Smut
Smut is easily transmitted by people and machinery
moving across infected areas. It is hard to detect and
may be widely distributed before it has been diagnosed.
The disease weakens the grass so that it succumbs to heat
and drought stress during the summer.
Symptoms are pale green new leaves with black streaks
between the veins. Spores are produced in the black
stripes and when the spores are liberated the leaf blade
becomes frayed. The tip of the leaf blade becomes
segmented, twisted and white.
Reduce spring and summer nitrogen fertilization on
infected lawns. Keep watering to prevent summer dormancy,
as any infected plants that go dormant will die.
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
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a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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