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The cause of turfgrass damage is often difficult to determine if
considerable time has elapsed between damage and diagnosis. Damage
is often blamed on disease or insects when there is no sound basis
for such a diagnosis. A careful diagnosis involves analysis of climatic
and environmental conditions, along with the management program
followed. It is important to know what fertilizers, insecticides,
fungicides, or herbicides have been applied, the amounts used, and
the time and method of application.
Height of Cut - Mowing is one of the most abused and least
understood turfgrass management practices. Shorter mowing reduces
leaf surface (the plant's food manufacturing factory) to such a
degree that the plant may have to draw food from its root reserves
to initiate new growth. Repeated defoliation reduces the root system,
and the plant will be weakened and unable to cope with adverse weather
conditions. It is important to know the correct mowing height for
your variety.
Frequency of Cut - Infrequent mowing, which has become increasingly
common with the popularity of the rotary mower, may remove excessive
amounts of clippings at each mowing. This may shock plants, causing
depleted root reserves and general weakening. Normally, no more
than one-fourth to one-third of the total leaf surface should be
removed at each mowing. Excessive clippings left on the turf may
injure or kill turf by smothering it. Hot, humid conditions under
these clippings are ideal for disease development.
Dull Mowers - Turf may have a gray to brown cast following
mowing. In most cases this discoloration can be attributed to dull
rotary mowers, although reel-type mowers may cause the same kind
of damage. Basically, the discoloration is due to tearing, splitting,
or shredding of the tips of the grass blades. Always keep any mower
sharp and properly adjusted.
Scalping - Most scalping occurs when attempts are made to
cut steep terraces crossways rather than up and down the terrace.
Scalping may also occur on poorly graded areas where one wheel of
the mower may drop into a surface depression, resulting in a closer
cut on that side of the mower.
Washboard Effect - Turfgrass areas regularly cut with rotary
mowers sometimes develop wave-like ridges running at right angles
to the direction of mowing. This washboard effect may be prevented
by regularly changing the direction of mowing. Alternating directions
of cut will partially control runners of creeping grasses and help
prevent grain and thatch.
Fertilizer Bands - Although fertilizer bands do not constitute
actual damage, they do result in a very unsightly appearance. The
fertilized area will be a brilliant green, whereas the unfertilized
area may vary from pale green to a chlorotic yellow color. Since
fertilizer materials seldom move laterally, every effort should
be made to distribute the material uniformly over the entire area.
Fertilizer Burn - Any type of fertilizer may cause fertilizer
burn if applied in excessive amounts or when grass blades are wet.
Soluble forms of nitrogen and potash are most likely to cause serious
burn. To avoid this problem, always apply fertilizer in recommended
amounts when grass is dry; if at all possible water thoroughly after
application.
Chlorosis - Turf areas may become pale green-yellow, and
plant growth may be somewhat stunted. In most cases this chlorotic
condition is due to lack of nitrogen. If a nitrogen fertilizer application
does not correct this condition, it is very likely that the cause
is iron deficiency. An application of iron sulfate or chelated iron
on turf showing iron deficiency will result in a greening of the
turf within a few hours after application.
Herbicide Injury - Some weed killers used to control specific
weeds may damage turfgrasses if applied at rates exceeding recommendations.
Unfortunately, many people feel that if "X" mls of material
per 100 m2 is recommended, "2X" mls of material per 100
m2 will do a better job. The result - turfgrass injury or death.
Always apply herbicides accurately at the manufacturer's recommended
rate. Avoid overlapping of spray pattern as this effectively doubles
the amount of chemical applied to the overlapped area.
Irrigation - Irrigating a turf area at a rate greater than
the soil's infiltration capacity may have deleterious effects. This
type of watering causes run-off and wastes one of our most expensive
commodities - water. More important, a thin surface crust may form.
This crust will impede the entrance of nutrients, insecticides,
air, and water into the soil. Such a crust also favors development
of weeds such as moss and algae.
Turfgrasses may also be damaged by frequent light watering. Frequent
shallow watering may keep upper soil layers near a constant saturation
point. This condition encourages shallow rooting and promotes weak
turf which is susceptible to disease and insect attack as well as
damage from traffic. For most turfgrass areas watering deeply only
when plants show signs of wilting is a sound watering program and
a big step forward in the development of healthy, vigorous turfgrasses.
Localized Dry Spots - Dead or injured spots often develop
in turf areas because of insufficient moisture, even though surrounding
turf shows no drought injury. Buried debris such as stumps, stones,
bricks, or gravel may result in a thin layer of soil overlaying
the area. This soil layer has a low water-holding capacity and dries
out very quickly. In other cases a large amount of thatch may act
as a thatched grass roof preventing water infiltration into the
soil.
Clover - Many people feel clover is desirable in a turf
area, but turf specialists and those involved in maintaining specialized
turf areas such as golf courses or athletic fields do not. Clover
often segregates into unsightly patches, is slippery and provides
poor footing, has low wear resistance, may be severely winter-damaged,
and forms seasonal white blossoms which interrupt the continuity
of the turf and attract bees. To eliminate clover, apply MCPA or
dicamba (Banvel).
Broadleaf Weeds - Weeds such as dandelion, broadleaf plantain,
and buckhorn (narrowleaf plantain) are easily controlled with 2,4-D.
More difficult to control broadleaf weeds such as knotweed, chickweeds,
heal-all, henbit, stitchwort, and sheep sorrel may require the use
of 2,4-D plus dicamba.
Moss and Algae - Moss and algae seldom invade a dense, healthy
turfgrass area. Infestations are usually associated with low soil
fertility, poor drainage, high soil acidity, improper watering,
too much shade, soil compaction, or a combination of these factors.
Diagnosis of the cause or causes of infestation followed by corrective
measures is the best control.
Helminthosporium Complex - this is a disease complex which
attacks leaf,crown and root is present on all turfgrass species.
Occurs during warm moist periods and causes reddish-brown to purplish-black
spots on leaves and stems. Spreads very quickly and leads to turf
and runner death.
 Spring
Dead Spot ( leptosphaeria spp.)- As turf growth resumes in the
spring, circular,bleached dead patches appear. These patches range
from a few centimeters to over 1 metre in diameter and can reappear
in the same spot for a number of years. Couch grass under intensive
management is most affected.Cool temperatures and moist soil are
conditions when causal fungi grow actively. Maximum injury occurs
when soil temperatures are around 15deg C. This is when couchgrass
activity is restricted, allowing the fungi to compete effectively.
 Rust
- Rust appears as reddish-brown to black pustules on grass blades
or stems. When severely rusted turf areas are walked on or mowed,
a cloud of red powder composed of spores may arise Although unsightly,
rust normally will not cause serious damage if the turf has been
well fertilized.
 Fairy
Ring - Fairy rings may appear as mushroom rings or as dark green
rings of vigorously growing turf varying from a few inches to many
feet in diameter. Fairy ring is caused by fungi living on decaying
organic matter such as stumps, logs, or scrap lumber from building
construction buried in the soil. The fungus grows out radially.
Nitrogen from the mycelium of the fungus is released, stimulating
growth and causing a dark green ring. During dry periods this stimulated
succulent growth may die from lack of moisture. There is no effective
chemical control. During dry periods keep the fairy ring well watered
to prevent loss of turf from moisture stress.
Slime Molds - Slime molds are nonparasitic fungi that live
on decaying soil organic matter. During wet summer periods these
fungi develop on grass blades, forming yellow to gray jelly-like
structures which later mature into gray to black spore masses. These
masses may damage the grass by shading or smothering. Normally,
slime mold will disappear during dry weather. Brushing infested
areas with a stiff broom will at least temporarily remove the unsightly
condition. If wet weather favorable to slime mold persists, control
the mold by applying any good turf fungicide.
Toadstools and Mushrooms - Heavy infestations of toadstools
and/or mushrooms often occur in turfgrass areas. These are saprophytic
fungi living on dead organic matter in the soil. There is no adequate
control, and these organisms will continue to appear, especially
during wet periods, as long as there is adequate organic matter
in the soil.
Insects
 Dollar
Spot - a disease of turfgrasses caused by the fungus Sclerotinia
homeocarpa, attacks most turfgrasses . Hybrid bermudagrasses, qld
blue couch and zoysia are most susceptible to dollar spot. The disease
occurs from autumn through to spring , and is most active during
moist periods of warm days (70-85°F) and cool nights (60°F)
. The disease is spread from one area to another by water, mowers,
other equipment or shoes.
Symptoms. On fine textured and close-cut
turf, the disease appears as round, brown to straw-colored and somewhat
sunken spots approximately the size of a silver dollar; thus, the
common name "dollar spot". In coarse textured grasses
maintained at taller cutting heights, the dead spots are larger
and more diffuse. Under these conditions dollar spot can be confused
with brownpatch, R. solani. Dollar spot is readily distinguished,
however, by characteristic lesions on the leaf blades of live plants
near the border of the affected area. Lesions are light tan with
a reddish-brown border, and usually radiate from the margins of
the leaf blade. On fine bladed grasses such as the lesions usually
girdle the leaf blade.
If the turf is examined when the disease is active early in the
day before the dew dries, cobweb-like mycelium of the fungus can
be seen growing on affected areas. During early stages of the disease,
affected plants may appear water-soaked and wilted, but spots quickly
fade to a characteristic straw color.
Disease Development. Several factors
influence the occurrence and severity of dollar spot. Qld blue couch,
hybrid bermudagrass and zoysia are most susceptible; while St. Augustine
and centipede are less frequently attacked by dollar spot.
Low soil moisture has been reported to enhance dollar spot activity,
but moisture from dew, light rain or irrigation must be present
on the foliage for the disease to develop.
The dollar spot fungus is capable of growth over a wide range of
temperatures (50° to 90°F), but disease development is greatest
at temperatures between 70° and 80°F. The dollar spot fungus
survives unfavorable temperature and moisture conditions in plant
tissue and thatch as dormant, compact masses of mycelium, called
sclerotia.
Low nitrogen and potassium levels in the soil have been reported
to increase the severity of dollar spot. Some rather severe outbreaks
of dollar spot have been brought under control by the application
of soluble nitrogen fertilizer. However, the beneficial effect of
nitrogen is thought to be due to rapid recovery of the grass during
periods of reduced disease activity. Research has shown that nitrogen
increases the susceptibility of grass to dollar spot.
Control. Cultural practices that promote
healthy turf help to reduce the occurrence and severity of dollar
spot.
- Remove excess thatch
- Keep fertility levels adequate
- Avoid light, frequent watering
- Mow frequently at recommended heights
- Aerate compacted soils
To prevent dollar spot apply a fungicide labeled for the disease
at recommended rates and intervals. Applications are most critical
during moist weather in the autumn and spring, when temperatures
are between 70º and 80ºF.
Insects 
Grubs - Grubs of a large range of beetles may severely damage
turf. Two common beetles are the African Black Beetle and the Argentinian
Scarab Beetle. These grubs feed on roots of the grass and when abundant
may completely sever the turf from the soil so that it can be rolled
up like a carpet. Grubs can be controlled with chlorpyrifos, diazinon
or trichlorfon . In severely damaged areas the severed turf should
be raked off prior to insecticide application and returfing..
Sod Webworm - The presence of small, buff colored moths flying
above the turf in a zig-zag pattern during the evening hours is
a sign of sod webworm infestation. The moths, harmless to turf,
are the adult stage of the webworm; immature larvae and the webworm
caterpillars damage the turf. The sod webworm constructs "silken
lined" tunnels in the soil; webworms emerge during the evening
or night to feed by clipping off grass blades at the soil surface.
During the daylight they hide in the tunnels. The first symptoms
of damage are small irregular patches of dead grass which enlarge
as damaged areas coalesce. Carbaryl , chlorpyrifos, or trichlorfon
applied in late afternoon or early evening will control sod webworm.
Billbug - Billbugs are weevils with hard snouts.
They burrow into soil and plant matter for food. Adult billbugs
are 6mm to 8mm long, with a slender grey body, and relatively long
legs. The young larvae tunnel through the stems and rhizomes of
the grass and damage may occur suddenly. Billbugs are a problem
in all turf growing areas
Other Pests
Dog Damage - The effect of dog urine on turfgrasses depends
upon the amount of soluble salts in the urine. When soluble salt
concentration is high, turf in the affected area will be killed.
Damaged areas are usually round or slightly irregular in shape and
variable in size. Nitrogen from urine with lower salt concentration
may stimulate vigorous dark green growth.
Soil Compaction - Soils of poor physical condition or those
subjected to play or heavy traffic (especially when wet) form an
impervious surface layer which prevents water infiltration, nutrient
penetration, and gaseous exchange between the soil and the atmosphere.
Under these conditions turfgrasses may thin out and be replaced
by weeds such as wireweed, which flourish on compacted soils. Aerating
machines will remove soil plugs or cores, creating an artificial
system of large pores which will permit moisture, nutrients, and
air to enter the soil and alleviate the compacted condition.
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Summer Scald - Poorly drained areas subject to water ponding
for short periods may be seriously damaged by scald. Summer thunderstorms
may release large amounts of water in a short period; if the storm
is followed by clearing and a hot sun, the sun's action on the ponded
water will produce anaerobic conditions which cause the damage.
As with winter scald, the only practical solution is to improve
drainage.
Thatch - Layers of partially decomposed leaves, stems, and
roots at the soil surface will build up over a period of years.
Thatch decreases turfgrass vigor by restricting the movement of
water, air, fertilizers, and pesticides into the soil. Roots are
normally quite shallow under thatch conditions, increasing the danger
of drought damage to the plant. Disease attacks may be accentuated
by thatch accumulations. Mechanical thatching equipment should be
used in spring or summer when grass recovery is rapid. It is best
to remove thatch accumulations in several treatments rather than
at one time.
Tree Competition - Trees, especially those with shallow feeder
roots, compete with grass for water, nutrients, and light. Where
there is heavy shade and/or many surface roots, it is best to plant
a ground cover rather than attempt to grow grass. Where competition
is less severe, improve turf by the following methods: (1) use shade-tolerant
grasses such as soft leafed buffalo (st.augustine); (2) fertilize
grass at 1 1/2 to 2 times the normal rate; (3) fertilize trees;
(4) water deeply and infrequently; (5) maintain a soil pH favorable
to the grass; (6) prune tree branches and roots as much as possible;
and (7) mow the grass higher than normal.
Fuel and Oil - Servicing or refueling power mowers or other
power equipment on the turfgrass area may cause considerable damage
from fuel or oil spillage. Because it is not immediately apparent,
this type of damage may be incorrectly diagnosed as disease, insect
damage, or dog injury. If the soil is saturated (especially with
oil) it may be some time before reseeding or returfing will be successful.
To avoid the problem always service or refuel power equipment off
the turfgrass area.
© Cleveland Turf 2002
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