White Grubs in Texas Turfgrass - Texas A&M AgriLife
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E-211
6/04
White Grubs in
Texas Turfgrass
Michael Merchant, Stephen Biles and Dale Mott*
White grubs are the larval stage of The most important turfgrass- grass include Cyclocephala pasade-
insects commonly known as May infesting white grubs in Texas are nae and Phyllophaga submucida.
or June beetles (or Junebugs). Texas the June beetle, Phyllophaga crinita
has almost 100 species of these bee- (Figure 2), and the southern Another interesting kind of white
tles, most of which do not cause masked chafer, Cyclocephala lurida. grub is the green June beetle,
significant economic damage to Warm season grasses like bermuda- Cotinus nitida. These rather large
crops or horticultural plantings. A grass, zoysiagrass, grubs feed primarily on decaying
few species, however, commonly St. Augustinegrass organic matter and normally do
damage turfgrass and other culti- and buffalograss not injure turf; however, turf can
vated plants. are attacked readily be damaged by their burrowing
by both types of activity. Larvae are especially com-
White grubs, sometimes referred to white grubs, with mon underneath fruit trees, in
as grubworms, injure turf by feed- most lawn damage compost piles and in soils with
ing on roots and other under- occurring during sum- high organic content, such as may
ground plant parts. Damaged areas mer and fall months. be found in heavily mulched gar-
within lawns lose vigor and turn dens and flower beds. Daytime
Figure 2. Adult white grubs, often
brown (Figure 1). Severely dam- resting places of green June beetle
aged turf can be lifted by hand or called May or June beetles, are com- larvae can often be found near
rolled up from the ground like a monly attracted to lights at night. such sites and are marked by small
carpet. mounds of soil on the lawn sur-
Cool season grasses such as the fes- face. The larvae have a curious
cues, bluegrass and ryegrass are habit of crawling on their backs
also susceptible to the June beetle across the soil surface to move
and southern masked chafer, from one site to another. Adults of
though such grasses tend to be the green June beetle are velvet-
attacked more frequently by a green on the top, metallic green
May beetle, Phyllophaga congrua. below and approximately one inch
Damage from May beetles often long. Adults fly during the day and
appears in the spring and early feed on over-ripe fruit.
summer, before injury from other
Figure 1. Golf course fairway dam- white grubs becomes evident.
*Extension Urban Entomologist and Extension
aged by white grubs. Other white grub species occasion- Agents-IPM, respectively, for Texas Cooperative
ally recorded as pests in Texas turf- Extension, The Texas A&M University System.
Life Cycle adult flight periods may not sub-
stantially reduce subsequent white
When cool weather arrives, white
grubs become dormant until the
Most turfgrass-feeding white grubs grub damage. Heavy white grub following spring. During this dor-
in Texas, such as the June beetle infestations often can be found in mant period white grubs do little
and southern masked chafer, areas with little or no outdoor or no feeding and cause little dam-
require 1 year to complete their life lighting. age. Occasionally white grubs will
cycle (a 2-year cycle is suspected in be found in turfgrass areas that fail
After mating, female beetles dig 2 to green up in the spring; however,
a portion of the grub populations
to 5 inches into the soil to lay eggs. the damage is primarily the result
in north Texas). The May beetle,
Each female can lay up to 30 to 40 of feeding that occurred the previ-
Phyllophaga congrua, requires 2
eggs, which hatch in approximate- ous fall. Spring and winter treat-
years to develop. For simplicity, the
ly two weeks. ments for white grubs with 1-year
following discussion will be limited
to species with 1-year life cycles. life cycles generally are ineffective
Larva. White grub larvae are in preventing turf damage.
Once a year, in late spring or creamy white and C-shaped, with
summer, adult beetles emerge from three pairs of legs (Figure 3). After Pupa. The pupal stage follows the
the soil to mate. Mated females hatching, the white grub passes third-instar and is the life stage
then return to the soil to lay eggs. through three larval life-stages, or during which the white grub trans-
Within about two weeks the eggs instars. These instars are similar in forms, or metamorphoses, into an
hatch into small white grubs that appearance, except for their size. adult beetle. The pupal stage does
feed on grass roots. The pupa, or First- and second-instars each not consume food and does not
intermediate stage between the require about 3 weeks to develop to move through the soil. This life
larva and the adult, occurs the fol- the next life-stage. The third-instar stage occurs during the spring and
lowing spring and is the last imma- actively feeds until cool weather lasts approximately 3 weeks. Pupae
ture phase of the insect's develop- arrives. Third-instar larvae are can be found in small earthen cells
ment cycle. Adults subsequently responsible for most turfgrass dam- three to six inches below the soil
emerge from the pupal stage when age due to their large size (1⁄ 2 to 1 surface. White grub treatments
environmental conditions are inch-long) and voracious appetites. applied during the pupal life stage
favorable in early- to mid-summer. Feeding by large numbers of third- are both ineffective and unneces-
Most damage from white grubs instar white grubs can quickly sary.
occurs during mid-summer to destroy turfgrass root systems, pre-
early-fall when the larger larvae are venting efficient uptake of food
actively feeding. and water. Damaged turf does not
grow vigorously and is extremely
Managing White Grubs
Adult. The adult stage of the susceptible to drying out, especial- Knowing when you have a prob-
various white grub species are ly in hot weather. lem. White grub damage can be
heavy-bodied beetles, 1⁄ 2 to 5⁄ 8 inch detected by the presence of irregu-
long, brown, with long, spindly lar-shaped areas of weakened or
legs (Figure 2). The June beetle and dying grass in the lawn. Less-
southern masked chafer emerge severely damaged turf lacks vigor
from the soil and fly at night, usu- and is more vulnerable to invasion
ally after a significant rainfall or by weeds. Depending on location
irrigation. Flight periods may last within the state, damage may
for several weeks, during which appear any time between the
time mating and egg-laying occur. months of June and October.
During flights, large numbers of Turfgrass damaged by white grubs
adult beetles, primarily males, may has a reduced root system and is
be attracted to lighted windows or easily pulled from the soil. Grubs
other lights at night. Females, should be readily found in the top
Figure 3. Turfgrass-infesting white
being less active fliers, usually are few inches of soil, in the turfgrass
grub larvae feeding on grass roots.
less common around lighted areas root zone. Turfgrass usually recov-
Grubs are most damaging when they ers from white grub damage by fall
than are males. For this reason, reach a length of 1⁄ 2- to 1-inch.
turning off outdoor lights during or the following spring.
At least one turfgrass disease, ing insects. These microscopic must be applied early enough to
Take-all Patch, can sometimes be worms can be purchased in stores kill the smaller (less than 1⁄ 2-inch-
mistaken for white grub damage. or through garden supply catalogs. long) larvae. Once white grubs
Take-all Patch occurs most fre- Commercial nematode products reach the third-instar life stage,
quently in spring and early sum- are usually designed to be mixed they are more difficult to control
mer and can be distinguished by with water and applied to lawns with the new products.
the rotted appearance of the roots. using a hose-end or hand-held
In contrast with white grub dam- sprayer. Recent research shows that The insecticides imidacloprid and
age, dead spots caused by Take-all under good conditions commer- halofenozide are used most today
Patch may persist into the summer cially-available nematodes can for white grub control. Imidaclo-
months. reduce white grub populations by prid is most effective against small-
50% or more. and medium-sized grubs but may
Some Texas lawns never suffer kill some grubs larger than 1⁄ 2 inch
white grub damage, while others Nematodes must be supplied with long. Imidacloprid trade names
are damaged year after year. If your adequate moisture to help them include Merit®, Bayer Advanced
lawn consistently dies out in move down into the soil where Lawn™ Season Long Grub Control
patches during late summer and if grubs are feeding. At least 1⁄ 4 inch and Scott's® Grub-Ex®. The lethal
you can verify that white grubs are of water should be applied before, effects of the insect growth regula-
the culprits, you may benefit from and another 1 ⁄ 4 inch of water tor halofenozide are limited to
a preventative treatment. On the applied just after, nematodes are early white grub life stages.
other hand, if you want to mini- sprayed on the lawn. These worms Halofenozide is ineffective if
mize your use of insecticides and pose no threat to humans or land- applied too late, after grubs have
don’t mind sampling for white scape plants and are an environ- reached the third-instar life stage.
grubs, follow the quick decision mentally sound alternative for Halofenozide trade names include
guide on page 6. By confirming those who prefer not to use pesti- Mach 2, Spectracide® Grub Stop™
that you have white grubs before cides on their lawn. and Hi-Yield® Kill-a-Grub™.
treating your yard, you can avoid
spending money on grub control One microbial pesticide, Bacillus Fortunately, both halofenozide and
and reduce pesticide use. popilliae, or milky spore disease, imidacloprid can be applied early
often is recommended for white and persist in the soil. Ideally, both
To confirm whether you need to grub (Japanese beetle) control in products should be applied within
treat for grubs, examine several soil other regions of the U.S.; however, six weeks of egg-laying. In south
sections at least 3 to 4 inches across it has not been shown to be effec- Texas, apply insecticides for white
and 4 inches deep (sample sandy tive against Texas turf-infesting grubs in early- to mid-June. In cen-
soils to greater depths). A good rule white grubs. tral and north Texas, the optimal
of thumb is to examine several soil treatment time is early- to mid-
plugs (up to one square foot per Spiked sandals sold for aerating July.
1000 square feet of turf) from wide- turf have been tried with some suc-
ly scattered parts of the lawn. Take cess for controlling damaging grub Where grub damage is already evi-
care to include areas at the edges of populations. According to one dent in lawns and larger grubs are
suspected grub damage. Finding study, repeatedly walking over present, use products containing
more than five white grubs per heavily infested turf with the trichlorfon or carbaryl. Because
square foot justifies treatment, spiked sandals may reduce grub they bind to soil particles and
although some lawns with even populations up to 50%. These san- remain close to the surface even
higher numbers of grubs may show dals are available through several after irrigation, pyrethroid insecti-
no damage. garden supply catalogs. cides (such as permethrin, esfen-
valerate, cyfluthrin and bifenthrin)
Non-chemical controls. Several Chemical control. Proper timing are less effective against white
non-chemical treatments are avail- and chemical application are criti- grubs, especially in clay soils.
able for controlling white grubs. cal to suppressing white grubs.
Beneficial nematodes within the New white grub insecticides are Post-treatment irrigation is essen-
genera Steinernema and Heterorhab- more persistent and less toxic to tial for all grub-control products.
ditis are tiny worms that attack beneficial arthropods and earth- To ensure that insecticides reach
white grubs and other soil inhabit- worms. However, these treatments the root zone, water-in liquid for-
mulations with 1⁄ 2 to one inch of aerifiers that remove small plugs of walks. Drop-type spreaders are less
water immediately after applica- soil can be rented to help remove likely to scatter pesticide granules
tion. Irrigate granular formulations thatch and enhance penetration of off of the target site than are
within 24 hours to wash the the turf by pesticides. Excessive rotary-type spreaders (Figure 4).
insecticide into the soil and thatch buildup is more likely to Pesticide runoff from improper
minimize the chance for exposure occur with hybrid bermudagrasses, pesticide applications reduces the
to people, pets and wildlife. Use a St. Augustinegrass and some effectiveness of a treatment and
rain gauge or straight-sided can to zoysiagrasses. Use of mulching can pollute above-ground and
verify application of sufficient irri- mowers to recycle grass clippings underground water supplies.
gation water. Two or more irriga- should not cause thatch buildup in
tion applications may be needed if regularly mowed lawns.
the soil is wet or difficult to pene-
trate. Water applied too quickly Environmental Considerations.
may cause run-off and pesticide Unnecessary insecticide applica-
loss. Irrigating the soil prior to tions sometimes create more prob-
insecticide application, particularly lems than they solve. Pesticides
when the soils are dry, can improve can have detrimental effects on
the effectiveness of insecticides. beneficial organisms, like earth-
For dry soils, apply 1⁄ 4 to 1⁄ 2 inch of worms, that help decompose
water the day before a treatment to thatch. Most insecticides do not Figure 4. Drop-type spreaders allow
improve spray penetration of the discriminate between "good" and precise placement of insecticide
soil and to encourage white grubs "bad" bugs and may kill beneficial granules.
to move closer to the soil surface. insects that help control other
This makes grubs easier to contact pests. Also, unnecessary pesticide
with the insecticide treatment. applications can increase the risk One should be aware that some
of insecticide resistance developing insecticides can be toxic to birds
Heavy thatch buildup can reduce among white grub and other pest and other wildlife. Always read and
the effectiveness of insecticide populations. For these reasons, follow label directions, including
sprays. Thatch is the accumulation routine, "preventative" insecticide the precautionary statements per-
of dead plant material, such as applications to lawns for white taining to potential environmental
dead grass stems, between the grub control are not recommend- hazards. Apply only the labeled
soil surface and the turfgrass ed. rates, avoid pesticide use near
foliage. Thatch layers greater than streams and ponds, and irrigate
1
⁄ 2 inch can result in greater suscep- Heavy rainfall can wash recently treatments promptly to help
tibility of the turf to plant diseases applied pesticides out of lawns, reduce the risk to non-target organ-
and can lead to other problems. especially if the ground is saturated isms, like birds. Never dispose of
Recent research has shown that with water when the treatment is leftover pesticides down sewer or
many pesticides bind to thatch, applied. Avoid treating lawns just storm water drains. Such actions
preventing them from reaching the before a heavy rain is expected. can cause toxicity to fish and other
soil and reducing their effective- Also try to avoid application of pes- aquatic organisms.
ness. Dethatching machines or soil ticides to street gutters and side-Tips for Professionals
■ Grubs of the southern masked chafer, monly found within the top few inches of soil.
Cyclocephala lurida, appear to be less destruc- One species, Sphenophorus venatus, is the
tive than Phyllophaga crinita grubs. An most common billbug collected from turf in
approximate economic threshold for masked Texas. This species can damage turfgrass, espe-
chafers is 8-10 grubs per square foot. The two cially zoysiagrasses and hybrid bermudagrass-
species can be distinguished by observing the es in the southeastern regions of the U.S., but
raster (hair patterns) on the underside tip of rarely damages turfgrass in Texas.
the abdomen (see Figure 5). A 10X hand lens
is sufficient to see these patterns on mature ■ Merit® and Mach 2® are trade names for pro-
white grubs. fessional formulations of imidacloprid and
halofenozide, respectively. Merit® may pro-
■ Sampling for white grubs can be done using a vide some late season grub control, but both
spade or knife to cut 6-inch square sections of products are best used early in the season,
turf, or by using a golf course cup cutter. Four, when grubs are less than 1⁄ 2-inch long.
six-inch squares or ten, four-inch cup cutter
core samples are equivalent to one square foot ■ Using surfactants in the spray solution may
of turf. improve control, especially in turf with heavy
thatch. Trichlorfon (Dylox®) is short-lived in
■ An insect that is occasionally mistaken for a high pH (greater than 7) soils and spray solu-
white grub is the billbug. Immature stages of tions. Add buffering agents to spray solutions
billbugs are small, white, legless larvae com- to increase stability of trichlorfon sprays.
a b c
Figure 5. White grub rastral patterns used in species identification are located in 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 courtesy Dr. Dave Shetlar, Ohio State
University.Quick Decision Guide for Grub Treatment Not sure you need to treat for grubs? Want to minimize your use of pesticides for economic or environmental reasons? Follow this quick decision guide. Remember that some treatments are effective only on small (less than 1 ⁄ 2 inch-long) grubs.
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