Many are harmless, some are beneficial, and some are pests. Only a few cause significant damage and need immediate control. Keep in mind that insects are only one of many potential causes for thin or brown grass.

1. Insects and Diseases
LNT 132 – Spring 2017
Mark Valen

2. Turf Disorders
• Definition: any disturbance caused by a living
organism or environmental factor that interferes
with plant growth, or plant appearance.
• Two classes of turf disorders:
• Abiotic
• Biotic

3. Turf Disorders
• Abiotic:
• temperature, water, or light stress
• nutrient deficiencies
• soil oxygen deficiencies
• air pollution
• soil acidity or alkalinity
• mechanical injury
• genetic defects

4. Turf Disorders
• Biotic:
• fungi
• bacteria
• viruses
• nematodes
• insects
• parasitic higher plants
• Fungi cause most of the turf diseases!
Host
PathogenEnvironment
Disease

5. Turf Insects
• Benefits of insects in Turf:
• burrowing insects provide soil aeration & better water
penetration.
• often decompose or eat thatch
• can aid in weed control by eating weed seedlings
• most soils insects are beneficial!

6. Turf Insects
• Damage turfgrasses by:
• direct eating of roots, rhizomes, stolons, or
shoots.
• sucking of plant juices
• transmitting diseases
• Symptoms:
• weak, yellowing plants
• defoliation of leaves and shoots
• lack of root system

7. Turf Insects
• Indicators of surface feeding insects:
• large numbers of birds feed on turf and peck holes into
turf
• small moths are seen, especially in the evening, flying
zig‐zag patterns over the surface of the turf.
• grass blades or complete plants are chewed off at the
soil surface (frass)
• turf dies along the sidewalks first (why – soil heats up
quicker and insect eggs hatch sooner)
• Typical surface feeding insects are:
• armyworms, cutworms, chinchbugs, flea beetles, frit
flies, sod webworms, & vegetable weevils.

8. Bermudagrass Mite
• Extremely small mite, with
wormlike shape.
• Adults and nymphs suck plant
juices from stems and inject
toxic saliva that shortens
internodes and swells leaf
sheaths, forming a witches’‐
broom growth pattern.
• Look for plants that are stunted
or swollen.
• Reduce nitrogen fertilizer, mow
closely, and remove mowing
clippings.

9. Billbugs ‐ Sphenophorus
• Small weevils, 1/3 inch long, with long, downward‐
pointing snouts and elbowed and clubbed antennae.
Difficult to find in turf. Larvae have no legs.
• All turfgrass species
• The affected area appears brown, thin, and dead in
small, irregular spots. Damage can spread to patches
extending many feet in width. Fine, whitish,
sawdustlike frass can be observed on the soil
surface. Damaged turf breaks at the crown and is
easy to pull from the soil, but cannot be rolled up
like sod damaged by white grubs.
• Dig around roots for whitish, C‐shaped, legless
grubs. Look for piles of frass. Inspect outdoor lights
around dawn for 1/3 inch beetles. Look for adults
crawling around sidewalks.
• If more than 1 billbug per square foot is found, you
may need to treat the area with an
insecticide. Beneficial nematodes are effective
against grubs

10. Cutworms and armyworms
• Adults are dull brown or grayish, relatively large
moths. Larvae are caterpillars that are up to 2 inches
long and often curl up and lie still when disturbed.
• All turfgrass species
• Larvae chew and cut leaves around the crown.
Damage begins in small, irregular spots and spreads
to patches extending many feet in width.
Armyworms, especially, prefer moist areas.
• Look for fat, dull gray, green, or brownish larvae up
to 2 inches long with a drench test. Inspect outdoor
lights around dawn for moths.
• Reduce thatch and eliminate soggy areas. If more
than 5 larvae per square yard are present, you may
need to treat. Beneficial nematodes or an
application of Bacillus thuringiensis (Bt) may be
effective against young caterpillars.

11. Masked chafers (white grubs)
• Golden brown beetles, 3/4 inch long with dark brown heads.
Larvae are white, C‐shaped grubs with dark stripes on their backs
and brown head capsules and legs.
• All turfgrass species
• Feed on the roots of turfgrass. Damage appears in late summer or
fall as irregular brown and dying patches. The ground often feels
spongy, and the lawn can be rolled up if heavily infested. Skunks,
moles and birds may be attracted to lawns with high grub
populations.
• Dig around the roots to look for grubs.
• Aerating the lawn can kill significant portions of the population if
they are feeding close to the soil surface.
• If more than 6 grubs are found per square foot, you may need to
treat. Tiphiid wasps are common parasites of masked chafers but
may not provide effective control. Beneficial nematodes may be
effective if applied when grubs are young. Other insecticides are
available including imidacloprid. Proper timing is essential.

12. Fiery skipper
• Resemble butterflies and are 1 inch with a hooked knob at
the end of their antennae. Males have orange‐yellow
wings with black spots, females have dark brown wings
with orange spots. Larvae are up to 1 inch and have
distinctive reddish markings on an oversized black head, a
narrowed neck followed by a dark thoracic shield, and a
greenish‐pink body color.
• Bermudagrass, creeping bentgrass, St. Augustinegrass
• Damage from fiery skippers begins as brown spots of lawn,
1 to 2 inches in diameter. Spots may join together to form
large, irregular dead patches. Leaves are chewed or
missing. Damage usually occurs near flower beds where
adults feed.
• Perform a drench test to bring up larvae. Look for adults
feeding on flowers.
• Reduce thatch. Overseed with grasses that are not
preferred. If more than 15 larvae are found per square
yard, you may need to treat. Beneficial nematodes or an
application of Bacillus thuringiensis (Bt) may be effective
against larvae.

13. Turf Diseases
• The Disease Cycle:
1. Inoculation
2. Penetration
3. Infection
4. Incubation
5. Overwintering
Host
PathogenEnvironment
Disease

14. Turf Diseases
• The Disease Cycle:
• Inoculation:
• spores land on plant.
• must have proper environmental conditions.
• must have susceptible host.
• spores germinate, grow a germ tube.
• control methods are very effective.

15. Turf Diseases
• The Disease Cycle:
• Penetration:
• germ tube enters host through a wound, stomate, or by direct
penetration.
• turf that exists in a succulent condition is more easily
penetrated.
• control measures at this point are still very good.

16. Turf Diseases
• The Disease Cycle:
• Infection:
• germ tube and mycelium begin to absorb nutrients from the
host.
• spores are now produced and can spread.
• control will stop current infection and future spread. Symptoms
have not been seen or are just starting.

17. Turf Diseases
• The Disease Cycle:
• Incubation:
• symptoms are now showing and dead areas are appearing in
turf.
• infected turf may be dead and other turf areas are showing
problems.
• control is fair at this point and curative rates of fungicide may
now be needed.

18. Turf Diseases
• The Disease Cycle:
• Overwintering:
• disease has stopped due to change of weather or other
favorable conditions.
• fungi survives as spores in soil, thatch, or turf.
• if optimum conditions reappear, the disease cycle begins again.

19. Turf Diseases
• Disease control by proper cultural practices:
• proper turfgrass selection
• proper maintenance practices
• proper fertilization
• proper watering
• proper mowing techniques
• proper sanitation
• proper drainage and air circulation

20. Dollar Spot
Hosts Annual bluegrass, Kentucky bluegrass, red fescue, tall fescue
Symptoms
Dollar spot begins as small, circular spots 1 to 2 inches in diameter.
Spots are straw colored or have a bleached appearance and merge
together to form large, irregular areas. Individual leaves appear
water‐soaked, often exhibiting 2 reddish bands across the leaf in an
hourglass shape. Fine, white, cobwebby threads may be seen in
early morning.
Conditions favoring disease
Dollar spot appears during the spring and fall months in California
and is favored by moderate temperatures (60° to 80°F). Excess
moisture, water stress, fog, or thatch buildup can also contribute to
disease development. Dollar spot survives in the soil as hard, dark
structures called sclerotia.
Prevention and management
Apply fertilizer at the recommended rate for your turf species.
Follow proper irrigation practices. Reduce thatch and maintain air
circulation. Compost top dressings may suppress the disease.
Increase your mowing height to the tallest recommended for your
turf species. If dollar spot has caused a problem in previous years, a
fungicide may be useful. Apply it in the early spring or fall before
symptoms occur.

21. Fairy Ring
Hosts All turfgrass species
Symptoms
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.
Conditions favoring disease
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.
Prevention and management
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. Deathwatch the lawn if the
thatch layer is more than 1/2 inch 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 and 2 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.

22. Fusarium Patch
Hosts Annual bluegrass creeping bentgrass, Kentucky bluegrass
Symptoms
Fusarium patch develops as circular patches 1 to 6 in 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.
Conditions favoring disease
Cool temperatures (40° to 60°F) and moist conditions favor Fusarium
patch. High nitrogen applications in the fall and neutral or alkaline
soils also contribute to disease development. Fusarium patch survives
in grass residues.
Prevention and management
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
Fusarium patch has been a serious problem in the past, have a
licensed pest control applicator apply a fungicide in the fall before
symptoms appear.

23. Powdery Mildew
Hosts All turfgrass species, but Kentucky bluegrass and
perennial ryegrass are most susceptible
Symptoms
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.
Conditions favoring 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.
Prevention and management
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.

24. Red Thread
Hosts Red fescue, perennial ryegrass
Symptoms
Red thread may kill grass in circular to irregular patches 2 to
8 inches 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.
Conditions favoring disease
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. In
California it occurs primarily in northern and central coastal
areas.
Prevention and management
Follow proper irrigation and fertilization requirements for
your turf species. Provide adequate air circulation and
reduce shading. Fungicides should not be needed.

25. Rhizoctonia Brown Patch
Hosts Annual bluegrass, Kentucky bluegrass, St. Augustinegrass,
tall fescue
Symptoms
Rhizoctonia blight first appears as irregular patches of weakened
grass that may enlarge to many feet in diameter. The affected
area may be a smoky color. Leaves and sheaths are watersoaked,
wilted, and light brown. Fungal threads may be apparent.
Conditions favoring disease
High temperatures (80° to 95°F) and high humidity favor the
development of Rhizoctonia blight. Excess thatch, poor drainage,
and soft, lush growth due to excessive nitrogen also contribute
to disease development.
Prevention and management
Reduce shading and improve soil aeration and water drainage.
Follow the irrigation and fertilization rates for your turf species.
Avoid watering in the evening. Dethatch when the thatch layer
exceeds 1/2 in. A fungicide may be useful if the disease was
severe in the past or for seedlings in young turf.

26. Rust
Hosts Annual bluegrass, Kentucky bluegrass, perennial
ryegrass, tall fescue
Symptoms
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.
Conditions favoring disease
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.
Prevention and management
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.

27. Spring Dead Spot
Hosts Bermuda grass
Symptoms
Spring dead spot appears in the lawn as circular areas of dead grass 6
to 12 inches wide. Spots coalesce to form large areas. Dark sclerotia
are often visible on stolons of affected plants. Sunken lesions can be
seen on affected crown buds, roots, and stolons.
Conditions favoring disease
The spring dead spot fungus colonizes dormant plants and grows most
rapidly when temperatures are 50° to 57°F. However, damage is
usually visible only after the grass emerges from dormancy in the
spring and healthy portions start to turn green. A thick thatch layer
and low mowing height also contribute to the development of the
disease. Spring dead spot survives as sclerotia in the soil and in
infected plant parts.
Prevention and management
Remove dead grass. Fertilize in the summer to maintain vigor but be
careful to not overfertilize in late summer. Follow irrigation
recommendations for your area and sprinkler output. Dethatch when
the thatch layer exceeds 1/2 inch thick. Raise your mowing height in
late summer or early fall to reduce pre‐dormancy stress. Overseeding
with ryegrass in the fall may be beneficial. Fungicides are available but
generally not needed.

28. Take‐all Patch
Hosts: Bentgrasses
Symptoms
Take‐all patch appears as circular or ring‐shaped dead
areas that range from a few inches up to 3 feet (90 cm) or
more in diameter. Roots are rotted and have dark strands
of mycelium visible on the surface. Large, black, globular,
fungal fruiting bodies (perithecia) may be visible with the
use of a hand lens.
Conditions favoring disease
Take‐all patch generally occurs in the late fall and winter
when temperatures are 50° to 60°F and soils are wet or
moist. However, symptoms may not appear until the turf is
exposed to periods of drought or heat stress. Soils light in
texture, low in organic matter, or underfertilized also
contribute to disease development.
Prevention and management
Improve soil drainage and fertilize at the recommended
rate for your turf species. A professional soil analysis can
provide you with information on amendments to add to
improve the soil.