White Grubs in Texas Turf Grass - The Urban Rancher

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WHITE GRUBS IN House and
TEXAS TURFGRASS Landscape Pests

M.E. Merchant and R.L. Crocker*

White grubs are the larval stage of masked chafer, Cyclocephala lurida. Another interesting kind of white
insects commonly known as May Warm season grasses like grub is the green June beetle,
or June beetles (or Junebugs). bermudagrass, zoysiagrass, St. Cotinus nitida. These rather large
Almost 100 species live in Texas, Augustinegrass, and grubs feed primarily on decaying
most of which do not cause signif- buffalograss are organic matter and normally do
icant economic damage to crops or attacked not injure turf; however, turf can
horticultural plantings. A few readily by be damaged by their burrowing
species, however, commonly dam- both types of activity. Larvae are especially com-
age turfgrass and other cultivated white grubs, mon underneath fruit trees, in
plants. with most compost piles, and in soils with
White grubs, sometimes referred lawn damage occur- high organic content, such as may
to as grubworms, injure turf by ring during summer be found in heavily mulched gar-
feeding on roots and other under- and fall months. dens and flower beds. Daytime
ground plant parts. Damaged resting sites of green June beetle
areas within lawns lose vigor and Figure 2. Adult white grubs, often larvae can often be found near
turn brown (Figure 1). Severely called May or June beetles, are com- such sites and are marked by
damaged turf can be lifted by monly attracted to lights at night. small mounds of soil on the lawn
hand or rolled up from the ground The optimal time to treat grub- surface. The larvae have a curious
like a carpet. infested lawns is 5-6 weeks after the habit of crawling on their backs
peak adult flights. across the soil surface to move
Figure 1. Golf course fairway dam- from one site to another. Adults
aged by white grubs. Cool season grasses such as the of the green June beetle are velvet-
fescues, bluegrass, and ryegrass green on the top, metallic green
The most important turfgrass- are also susceptible to the June below, and are approximately 1
infesting white grubs in Texas are beetle and southern masked inch in length. Adults fly during
the June beetle, Phyllophaga crinita chafer, though they tend to be the day and feed on over-ripe
(Figure 2) and the southern attacked more frequently by a fruit.
May beetle, Phyllophaga congrua.
*Extension Urban Entomologist and Damage from May beetles often Life Cycle
Research Entomologist, respectively, The appears in the spring and early
Texas A&M University System. summer, before injury from other Most turfgrass-feeding white
white grubs becomes evident. grubs in Texas, such as the June
Other white grub species occasion- beetle and southern masked
ally recorded as pests in Texas chafer, require one year to com-
turfgrass include Cyclocephala plete their life cycle (a two-year
pasadenae and Phyllophaga sub- cycle is suspected in a portion of
mucida. the grub populations in north
Texas). The May beetle,
Phyllophaga congrua, requires two
years to develop. For simplicity,
the following discussion will be

Texas Agricultural Extension Service • Zerle L. Carpenter, Director • The Texas A&M University System • College Station, Texas

limited to species with one-year passes through three larval life- spring and lasts approximately
life cycles. stages, or instars. These instars are three weeks. Pupae can be found
similar in appearance, except for in small earthen cells 3 to 6 inches
Once a year, in late spring or sum- their size. First- and second-instars below the soil surface. White grub
mer, adult beetles emerge from the each require about three weeks to treatments applied during the
soil to mate. Mated females then develop to the next life-stage. The pupal life stage are both ineffec-
return to the soil to lay eggs. third-instar actively feeds until tive and unnecessary.
Within about two weeks the eggs cool weather arrives. Third-instar
hatch into small white grubs that larvae are responsible for most Managing White
feed on grass roots. The pupa, or turfgrass damage due to their
intermediate stage between the large size (1/2 to 1 inch long) and Grubs
larva and the adult, occurs the fol- voracious appetites. Feeding by
lowing spring and is the last large numbers of third-instar K nowing when you have a
immature phase of the insect’s white grubs can quickly destroy
development cycle. Adults subse- turfgrass root systems, preventing problem. White grub damage can
quently emerge from the pupal efficient uptake of food and water. be detected by the presence of
stage when environmental condi- Damaged turf does not grow vig- irregular-shaped areas of weak-
tions are favorable in early- to orously and is extremely suscepti- ened or dying grass in the lawn.
late-summer. Most damage from ble to drying out, especially in hot Less-severely damaged turf lacks
white grubs occurs during mid- weather. vigor and is more vulnerable to
summer to early fall when the invasion by weeds. Depending on
larger larvae are actively feeding. Figure 3. Turfgrass-infesting white location within the state, damage
grub larvae feeding on grass roots. may appear anytime between the
A dult. The adult stage of the Grubs are most damaging when months of June and October.
they reach a length of 1/2 to 1 inch. Turfgrass damaged by white
various white grub species pro- grubs has a reduced root system
duces heavy-bodied beetles, 1/2 When cool weather arrives, white and is easily pulled from the soil.
to 5/8 inch long, brown, with grubs become dormant until the Grubs should be readily found in
long, spindly legs (Figure 2). The following spring. During this dor- the top few inches of soil, in the
June beetle and southern masked mant period white grubs do little turfgrass root zone. Turfgrass
chafer emerge from the soil and or no feeding and cause little dam- usually recovers from white grub
fly at night, usually after a signifi- age. Occasionally white grubs will damage by fall or the following
cant rainfall or irrigation. Flight be found in turfgrass areas that spring.
periods may last for several fail to green up in the spring;
weeks, during which time mating however, the damage is primarily At least one turfgrass disease,
and egg-laying occur. During the result of feeding that occurred Take-all Patch, can sometimes be
flights, large numbers of adult the previous fall. Spring and win- mistaken for white grub damage.
beetles, primarily males, may be ter treatments for white grubs Take-all Patch occurs most fre-
attracted to lighted windows or with one-year life cycles generally quently in spring and early sum-
other lights at night. Females, are ineffective in preventing turf mer, and can be distinguished by
being less active fliers, usually are damage. the rotted appearance of the roots.
less common around lighted areas In contrast to white grub damage,
than are males. For this reason, P upa. The pupal stage follows dead spots caused by Take-all
turning off outdoor lights during Patch may persist into the summer
adult flight periods may not sub- the third-instar and is the life months.
stantially reduce subsequent white stage during which the white grub
grub damage. Heavy white grub transforms, or metamorphoses, Most Texas lawns probably do not
infestations often can be found in into an adult beetle. The pupal experience damaging numbers of
areas with little or no outdoor stage does not consume food and white grubs in any given year.
lighting. does not move through the soil. For this reason, lawns should be
This life stage occurs during the inspected for grubs before a deci-
After mating, female beetles dig 2 sion is made to treat. The best time
to 5 inches into the soil to lay to inspect for grubs is when they
eggs. Each female can lay up to 30 are small (1/2 inch or less). By
to 40 eggs, which hatch in approx- detecting white grubs early, treat-
imately two weeks. ments can be applied before seri-
ous root damage occurs. Also, con-
L arva. White grub larvae are trols are more effective when
applied to smaller larvae.
creamy white and C-shaped, with
three pairs of legs (Figure 3). Several sites in the lawn should be
After hatching, the white grub examined to find out if treatment

is needed. Soil sections at least 3 Amarillo
to 4 inches across and 4 inches Late July-
deep (deeper samples may be early August
advisable in sandy soils) should be
examined for grubs. A good rule Dallas
of thumb is to examine several soil Late July-Aug
plugs (up to one square foot per
1,000 square feet of turf) from El Paso San Angelo
widely scattered parts of the lawn, Late June- Mid July-Aug
being careful to include areas of early July
suspected grub damage. Treat-
ment is justified when more than San Antonio Houston
five white grubs per square foot Mid June- Mid-late
are found, although some lawns early July July
may be able to sustain higher
numbers without noticeable Weslaco Corpus Christi
damage. June Late June-early July

W hen to treat. The best time Figure 4. Optimal treatment times for white grubs in Texas.

to inspect for grubs and apply research shows that under good grub populations. According to
insecticides occurs approximately conditions commercially-available one study, repeatedly walking
five to six weeks after the heaviest nematodes can reduce white grub over heavily infested turf with the
June beetle flights. Peak June bee- populations by up to 50 percent. spiked sandals may reduce grub
tle flights occur at different times populations up to 50 percent.
of the year in different parts of the Nematodes must be supplied with These sandals are available
state. Within a given locale, flight adequate soil moisture to help through several garden supply
periods may vary as much as two them move down into the soils catalogs.
months from year to year, due to where grubs are feeding. At least
variations in rainfall. 1/4 inch of water should be C hemical control. Proper tim-
applied before, and another 1/4
In some areas, May or June beetle inch of water applied just after, ing of insecticide treatments is one
species that do not attack turf may nematodes are sprayed on the of the most critical elements for
become abundant at lights and lawn. These worms pose no threat successful suppression of white
cause confusion about when to to humans or landscape plants, grubs. Both chemical and biologi-
treat. For this reason, it’s best to and are an environmentally sound cal control measures are most
consult with your local county alternative for those who prefer effective when applied against
Extension office to confirm the not to use pesticides on their lawn. smaller (less than 1/2 inch long)
optimal treatment period for your larvae, and less effective against
area. Generalized guidelines for One microbial pesticide, Bacillus eggs, larger larvae, and pupae.
the best inspection and treatment popilliae, or milky spore disease, The residual effectiveness of most
times for major metropolitan often is recommended for white insecticides is greatly reduced one
areas in Texas are summarized grub (Japanese beetle) control in to two weeks after application;
in Figure 4. other regions of the U.S.; however, thus, insecticides applied too early
it has not been shown to be effec- may not remain effective in the
N on-chemical controls. tive against Texas turf-infesting soil through the egg hatch period.
white grubs. Insecticides applied after the opti-
Several non-chemical treatments mal treatment period are often less
are available for controlling white Spiked sandals sold for aerating effective because white grubs have
grubs. Beneficial nematodes with- turf have been tried with some become large and difficult to kill.
in the genera Steinernema and success for controlling damaging
Heterorhabditis are tiny worms that
attack white grubs and other soil
inhabiting insects. These micro-
scopic worms can be purchased in
stores or through garden supply
catalogs. Commercial nematode
products are usually designed to
be mixed with water and applied
to lawns using a hose-end or
hand-held sprayer. Recent

If grubs are restricted to certain Heavy thatch buildup can reduce just before a heavy rain is expect-
areas of a yard, treat the infested the effectiveness of insecticide ed. Also try to avoid application
areas only. sprays. Thatch is the accumula- of pesticides to street gutters and
tion of dead plant material, such sidewalks. Drop-type spreaders
Effective white grub insecticides as dead grass stems, between the are less likely to scatter pesticide
for use by consumers include soil surface and the turfgrass granules off the target site than are
chlorpyrifos (Dursban®), diazinon, foliage. Thatch layers greater than rotary-type spreaders (Figure 5).
imidacloprid (Merit®) and isofen- 1/2 inch can result in greater sus- Pesticide runoff from improper
phos (Oftanol®). A decline in ceptibility of the turf to plant dis- pesticide applications reduces the
white grub numbers should be eases and can lead to other prob- effectiveness of a treatment and
observed within 2 to 3 weeks after lems. Recent research has shown can pollute above-ground and
treatment. Properly timed and that many pesticides bind to underground water supplies.
applied chemical treatments thatch, preventing them from
should be effective with only one reaching the soil, and reducing Figure 5. Drop-type spreaders allow
application. When using imidaclo- their effectiveness. Dethatching precise placement of insecticide
prid, applications should be made machines or soil aerifiers (that granules.
before damage becomes evident, remove small plugs of soil) can be
as this product is most effective rented to help remove thatch and One should be aware that certain
against first- and second-instar enhance penetration of the turf by insecticides can be highly toxic to
larvae. pesticides. Excessive thatch birds and other wildlife. Always
buildup is more likely to occur read and follow label directions,
Irrigating the soil prior to insecti- with hybrid bermudagrasses, St. including the precautionary state-
cide application, particularly Augustinegrass and some zoysia- ments pertaining to potential envi-
when the soils are dry, can grasses. Use of mulching mowers ronmental hazards. Apply only
improve the effectiveness of insec- to recycle grass clippings should the labeled rates, avoid pesticide
ticides. For dry soils, apply 1/4 to not cause thatch buildup in regu- use near streams and ponds, and
1/2 inch of water the day before a larly mowed lawns. irrigate treatments promptly to
treatment to improve spray pene- help reduce the risk to non-target
tration of the soil and to encour- E nvironmental organisms like birds. Diazinon is
age white grubs to move closer to especially toxic to birds and has
the soil surface. This makes grubs considerations. Unnecessary been a problem contaminant in
easier to contact with the insecti- insecticide applications sometimes many community wastewater and
cide treatment. create more problems than they stormwater effluents. Particular
solve. Pesticides can have detri- care should be taken when using
Post-treatment irrigation is essen- mental effects on beneficial organ- this product where songbirds or
tial. Liquid insecticide formula- isms, like earthworms, that help other birds are abundant or where
tions must be watered-in with 1/2 decompose thatch. Most insecti- contamination of surface water
to 1 inch of water immediately cides do not discriminate between may occur. Never dispose of left-
after application to ensure that “good” and “bad” bugs and may over diazinon or any other pesti-
insecticides reach the root zone. kill beneficial insects that help cide down sewer or stormwater
Granular formulations should be control other pests. Also, uneces- drains. Such actions can cause tox-
irrigated within 24 hours to wash sary pesticide applications can icity to fish and other aquatic
the insecticide into the soil and increase the risk of insecticide organisms.
reduce the chance for the insecti- resistance developing among
cide to be picked up by birds or white grub and other pest popula-
other wildlife. A rain gauge or tions. For these reasons, routine,
straight-sided can should be used “preventative” insecticide applica-
to verify that sufficient irrigation tions to lawns for white grub con-
water has been applied. Two or trol are not recommended.
more waterings may be needed to
apply sufficient water if the soil is Heavy rainfall can wash recently
wet or difficult to penetrate. If applied pesticides out of lawns,
water is applied too quickly, especially if the ground is saturat-
runoff and loss of pesticide may ed with water when the treatment
occur. is applied. Avoid treating lawns

For more information on pests, pest control and pesticide products,
please see Extension publication B-1373, House and Landscape Pests.

Tips for professionals

s Grubs of the southern masked chafer, of soil. One species, Sphenophorus venatus, is
the most common billbug collected from turf
Cyclocephala lurida, appear to be less destruc- in Texas. This species can damage turfgrass,
tive than Phyllophaga crinita grubs. An especially zoysiagrasses and hybrid bermu-
approximate economic threshold for masked da-grasses in the southeastern regions of the
chafers is 8 to 10 grubs per square foot. The U.S., but rarely damages turfgrass in Texas.
two species can be distinguished by observ-
ing the raster (hair patterns) on the under- s Additional chemical treatments available to
side tip of the abdomen (see Figure 6). A
10X hand lens is sufficient to see these pat- commercial pesticide applicators include
terns on mature white grubs. bendiocarb, carbaryl, fonophos, ethoprop,
isofenphos, imidacloprid and trichlorfon.
s Sampling for white grubs can be done using Trichlorfon is subject to rapid breakdown in
high pH soils or waters. Imidacloprid
a spade or knife to cut 6-inch square sections should only be used before grub damage
of turf, or by using a golf course cup cutter. becomes evident. Chlorpyrifos treatments
Four 6-inch squares or 10 4-inch cup cutter may be less effective than other treatments
core samples are equivalent to one square in soils with high organic matter content or
foot of turf. thatch buildup.

s An insect that is occasionally mistaken for a s Use of surfactants in the spray solution may

white grub is the billbug. Immature stages improve control, especially in turf with
of billbugs are small, white, legless larvae heavy thatch.
commonly found within the top few inches

Figure 6. White grub rastral patterns used in species identification are located at the anus (a) and can be observed with a
10X hand lens. June bug larvae, Phyllophaga spp., can be recognized by their seagull-shaped anal slit ( ) and by the
two parallel rows of spines running longitudinally under the anus (b). Masked chafer larvae, Cyclocephala sp., can be
recognized by their straight anal slit (—) and the random placement of spines beneath the anus (c). Scanned images cour-
tesy Dr. Dave Shetlar, Ohio State University.

Quick Decision Guide for Grub Treatment

Have you seen numerous If you found
adult beetles attracted to fewer than 5,
lighted windows or outdoor no treatment
lights? is needed.

Wait 4 to 5 weeks, then sample sites.
Be sure to check sites with previous
history of white grub damage.

Did you find 5 grubs or more
per square foot?

If yes, treatment is needed.

If you found 5 or more grubs per square
foot, apply appropriate treatment
according to label directions.

Water treatment thoroughly (1/2 to 1 inch
of irrigation) to move pesticide down to
root zone where grubs feed.

Properly dispose of any pesticide
containers according to label directions.
NEVER pour leftover pesticide down
drains or storm sewers.

Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age
or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and
June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service,
The Texas A&M University System.