Lawn Diseases
I am dedicating this page of my website to illustrating through photographs, the most
common lawn insect, disease, and animal damage issues that most homeowner could
experience on their lawn. I will also give you what I believe to be the best
preventative measures and solutions to these problems. I will start with lawn
diseases, followed by insect problems, and finish up with animal damage.
Brown patch disease (Rhizoctonia solani) The name "brown patch" best
describes symptoms of this disease. It usually comes during hot, humid, and rainey
periods and generally after June 15th, in our area. Expanding patches of discolored
grass up to several feet in diameter mark the presence of a severe outbreak. The
affected turf may turn brown primarily at the leading edge of the patch while the grass
in the center, though thinned, may remain green. Diseased areas are sometimes
diffuse and not so clearly circular. On individual grass blades, lesions of various sizes
occur which have bleached centers and purplish-brown margins. Where disease is
severe, the affected area may look sunken.
Brown patch disease (Rhizoctonia solani) Prevention/Solutions
How to Prevent Brown Patch Lawn Disease
Watering infrequently can help keep the grass as dry as possible. Also, try to water
only early in the morning to prevent wet grass in the evenings. Control thatch by
dethatching or aerating your lawn and make sure to follow a good annual fertilizer
program. Stick with slow-release nitrogen fertilizer and try not to fertilize during heavy
rains when the lawn is most saturated. Apply fungicide in mid June as a preventative.
How to Treat Brown Patch on Lawns
You can cure brown patch by using a contact fungicide. It is important that you treat
the disease as soon as possible and continue to apply fungicide at three to four week
intervals, as long as humid, warm weather persists. There are plenty of fungicides at
your local Garden Center or at the Home Depot that are labeled for treatment of this
disease.
Dollar spot fungus You can identify dollar spot disease in your lawn in two
ways. The first way is through the size and shape of the area that is damaged. Usually,
individual spots are very distinct and circular in shape, which are only a few inches in
diameter. Another sign of dollar spot disease is the appearance of lesions on grasses.
The disease can cause bands in hourglass shape across the grass blade, which is light
tan in color with a reddish-brown edge. It can kill the entire grass and your lawn may
need reseeding or renovation to control the disease.
Dollar spot disease Prevention/Solutions
How to Prevent Dollar Spot Lawn Disease
Keep your lawn well irrigated. It is necessary to saturate your soil regularly because
grass diseases including the dollar spot occur in soil with low moisture. However,
make sure to avoid watering frequently during the late afternoons or evening.
How to Treat Dollar Spot on Lawns
Use proper mixture of fertilizers in correcting the nitrogen fertility during the times of
the disease activity. You can apply treatments such as fungicide in getting rid of
dollar spot disease. However, fungicide is not required in residential lawns if the
levels of nitrogen fertility are managed properly and other cultural stresses are
lessened. Dollar spot disease has different degrees of fungicide tolerance and there
are some strains of dollar spot that have become resistant to fungicide, so a particular
fungicide may be effective to one disease but not to another. You need to have a
balanced nitrogen fertility program to control the disease because dollar spot disease
is known to be most severe on nitrogen-deficient soil. With a balanced nitrogen soil,
the outbreak of the disease will be delayed in the spring and the severity of outbreaks
will be reduced. In addition, the performance of fungicide will improve and the
recovery of turf will be faster.
Fairy ring (Agrocybe spp., Marasmius oreades, Lepiota spp.) Fairy ring
symptoms vary depending on the species of fungus. A dark green band of turf may
develop in a circle or semi-circle, or a ring of brown, dying grass may occur.
Mushrooms may or may not be present. White, fungal mycelia may be observed
under the thatch layer. Soils with a thick thatch layer or undecomposed organic
matter favor disease development. Lawns with low fertility or insufficient water tend
to have more damage than lawns with adequate fertilizer and water.
Fairy ring Prevention/Solutions
How to manage Fairy ring
Apply adequate nitrogen to mask symptoms and increase activity of beneficial soil
organisms. To improve water penetration, aerate and water heavily in holes for
several days. De thatch the lawn if the thatch layer is more than 1/2 inch (1.2 cm) thick.
Rake mushrooms to improve the appearance of the turf. Dig out the turf and root zone
that contains a white, cottony mass to a depth of 12 inches (30 cm) and 2 ft (60 cm)
beyond the outer edge of the ring. Refill the area with clean soil and reseed or re-sod.
Fungicides are available but they have not been observed to reliably control fairy ring.
Pythium blight (Grease spot) — Pythium spp.
Pythium blight infestations start out as small, circular spots of dead grass that run
together as the infection spreads. When it is hot and conditions are favorable, this
disease can spread rapidly in a 24-hour period. Infected leaf blades blacken and
rapidly wither and later turn reddish-brown. Leaves lie flat, stick together, and appear
greasy. Masses of white, cottony mycelia may appear. Pythium blight occurs in parts
of the lawn where it is wet and often runs with the pattern of water drainage.
Pythium blight tends to develop in low spots that remain wet. Temperatures between
80° and 90°F favor disease development. High nitrogen levels also contribute to the
disease.
Pythium blight Prevention/Solutions
How to manage Pythium blight
The key to preventing and managing Pythium blight is proper irrigation. Avoid
overwatering and improve soil aeration and drainage. Do not mow when the leaf
blades are wet and avoid applying excess nitrogen during hot, humid weather.
Reduce shading. Fungicides should be used in severe cases only.
Leaf spot (Bipolaris spp.)
Infected leaves, sheaths and stems have circular to elongated brownish spots with
brown centers and dark brown or purple borders. Crowns and roots have a dark brown
rot. Symptoms may occur throughout the lawn rather than in clumped areas. Plants
may die in hot, windy weather, leaving thinned areas throughout the turf.
Warm temperatures (70° to 90°F) and high humidity favor the development of leaf
spot. Weakened turf may be the result of poor cultural practices. Mowing too short and
applying high amounts of nitrogen contribute to the development of the disease.
Leaf spot Prevention/Solutions
How to manage Leaf spot
Reduce shade and improve soil aeration and water drainage. Follow the
recommended irrigation requirements for your turf species and avoid excess nitrogen
fertilizer. Maintain as high a mowing cut as possible. Apply fungicide in severe cases.
Powdery mildew (Erysiphe graminis)
Leaf surfaces are covered with a grayish white powdery growth. Isolated patches may
spread to larger areas of the lawn. Leaf blades may turn pale yellow in later stages of
the disease. Cool temperatures (about 65°F), high humidity, and poor air circulation
favor the development of powdery mildew. The disease is most severe in shady areas.
Powdery mildew Prevention/Solutions
How to manage Powdery mildew
Reduce shade and improve soil aeration. In areas where powdery mildew is a
problem, plant less susceptible species. Follow proper irrigation and fertilization
recommendations for your turf species. Mow at the high end of the recommended
height for your species. Fungicides are usually not warranted. Apply proper fungicide,
if severe.
Red thread (Laetisaria fuciformis)
Red thread may kill grass in circular to irregular patches 2 to 8 inches (5 - 20 cm) in
diameter or it may weaken turf. Leaves turn tan in color, giving the turf a scorched
appearance. Infections on leaves begin at the tip and move down the blade. A pink
web of fungal threads binds the leaves together. Pink, gelatinous fungal crusts occur
on the leaves.
Red thread is favored by mild air temperatures (60° to 75°F) and extended periods of
leaf wetness. Plants deficient in nitrogen during periods of cool temperatures or
excess wetness can make the turf more susceptible to infection.
Red thread Prevention/Solutions
How to manage Red thread
Follow proper irrigation and fertilization requirements for your turf species. Provide
adequate air circulation and reduce shading. Fungicides should not be needed. Apply
the proper fungicide.
Fusarium blight (Fusarium culmorum, F. tricinctum)
Lawns infested with Fusarium blight have small, circular grayish to straw-colored
areas of dead grass. These circular spots may range from a few inches up to a foot in
diameter. Some plants in the center may survive, giving the turf a frog-eye
appearance. The crown or basal area of dead stems has a reddish rot and is hard and
tough. The dead foliage appears straw-colored.
Daytime temperatures of 85° to 95°F favor Fusarium blight. Drought-stressed areas in
full sun are most likely to exhibit the disease. Fusarium blight survives in thatch and
grass residues.
Fusarium blight Prevention/Solutions
How to manage Fusarium blight
Follow proper fertilization and irrigation requirements for your turf species. When
overseeding bluegrass, use a mixture of 20% perennial ryegrass. Mow at the highest
recommended height for your turf species. Dethatch if you have a thatch layer more
than 1/2 inch (1.2 cm) thick. Consider replanting with other turf species that are not
susceptible to Fusarium blight. Fungicides are available but do not give complete
control. If used, make spring applications before or just after symptoms appear.
Red thread (Laetisaria fuciformis)
Red thread may kill grass in circular to irregular patches 2 to 8 inches (5 - 20 cm) in
diameter or it may weaken turf. Leaves turn tan in color, giving the turf a scorched
appearance. Infections on leaves begin at the tip and move down the blade. A pink
web of fungal threads binds the leaves together. Pink, gelatinous fungal crusts occur
on the leaves.
Red thread is favored by mild air temperatures (60° to 75°F) and extended periods of
leaf wetness. Plants deficient in nitrogen during periods of cool temperatures or
excess wetness can make the turf more susceptible to infection.
Rust (Puccinia striiformis, P. graminis, P. coronata, and Uromyces spp)
Affected leaves and stems turn yellow and are covered with reddish-brown pustules
with dusty spores. The yellow spots start small but the entire leaf may soon turn
yellow. The entire turf may take on a rusty color and look thin and weak. Orange
spores rub off when leaves are handled.
Moderately warm air temperatures (70° to 75°F) and extended periods of leaf wetness
favor the development of rust. Turf that is deficient in nitrogen is more susceptible to
disease development.
Rust Prevention/Solutions
How to manage Rust
Maintain turfgrass vigor by following proper irrigation and fertilization requirements for
your turf species. Mow regularly and remove the clippings to reduce the number of
spores if the lawn is infected . Rust can be managed by following proper cultural
practices, and fungicides should not be needed. Apply the proper fungicide.
Rust (Puccinia striiformis, P. graminis, P. coronata, and Uromyces spp)
Affected leaves and stems turn yellow and are covered with reddish-brown pustules
with dusty spores. The yellow spots start small but the entire leaf may soon turn
yellow. The entire turf may take on a rusty color and look thin and weak. Orange
spores rub off when leaves are handled.
Moderately warm air temperatures (70° to 75°F) and extended periods of leaf wetness
favor the development of rust. Turf that is deficient in nitrogen is more susceptible to
disease development.
Slime mold (Physarum cinereum)
Slime molds on turf may cause the grass to temporarily turn yellow because they
block the sun, but once the slime dries out and disappears the grass quickly recovers.
Slime molds are usually considered beneficial organisms because they decompose
dead organic matter and help the cycling of nutrients. They also may consume plant
pathogenic fungi or bacteria in the soil, helping to reduce plant disease.
Slime mold Prevention/Solutions
How to manage Slime mold
Because slime molds thrive in a moist environment, the best way to get rid of them is
to allow them to dry out. Raking the grass to introduce air helps to accomplish this.
Slime mold on turf also can be simply mowed off. Heavy thatch in the lawn provides a
reservoir of organic matter and moisture, so reducing the thatch layer may help
reduce slime mold growth. Chemical treatments rarely work.
Slime mold (Physarum cinereum)
Slime molds on turf may cause the grass to temporarily turn yellow because they
block the sun, but once the slime dries out and disappears the grass quickly recovers.
Slime molds are usually considered beneficial organisms because they decompose
dead organic matter and help the cycling of nutrients. They also may consume plant
pathogenic fungi or bacteria in the soil, helping to reduce plant disease.
Snow mold pink (Microdochium nivale) (FusariumPatch)
Snow mold patch develops as circular patches 1 to 6 inches (2.5 - 15 cm) wide. Leaves
appear watersoaked and are reddish-brown on the outside progressing to a straw
color in the center. Dead leaves may have gelatinous spore masses. White or pink
fungal threads may be observed in the early morning, giving the turf a pink cast.
Cool temperatures (40° to 60°F) and moist conditions favor Snow mold fusarium patch.
High nitrogen applications in the fall and neutral or alkaline soils also contribute to
disease development. Snow mold patch survives in grass residues.
Snow mold Pink Prevention/Solutions
How to manage snow mold
Reduce shade and provide good soil aeration and water drainage. Irrigate at the
recommended frequency for your turf species and avoid excess nitrogen fertilizer,
especially in the fall. Maintain a soil pH between 6.5 and 6.7. You may need to have a
professional soil analysis done to help you determine what amendments to add to
maintain an ideal pH. High levels of potassium suppress disease. If Snow mold has
been a serious problem in the past, have it treated with a fungicide product labeled for
it's treatment.