Japanese Beetle - Colorado Master Gardener
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Japanese Beetle
Fact Sheet No. 5.601 Insect Series| Home and Garden
by W. Cranshaw*
For close to a century, the Japanese Quick Facts
beetle (Popillia japonica) has been one
of the most seriously damaging insect • Japanese beetle adults chew
pests of both turfgrass and landscape flower blossoms and leaves
plants over a broad area of the eastern of many commonly grown
US. Recently, there have become a few plants.
permanent, reproducing populations
of this insect in some communities • Japanese beetle larvae are a
along the Front Range of Colorado. At type of white grub that feeds
some of these sites high numbers of on the roots of grasses.
Japanese beetles now regularly occur
• Adults are best controlled
and adult beetles are causing significant
Figure 2. Japanese beetle damage to leaves of by handpicking or by use of
damage to leaves and flowers of many
grape. certain insecticide sprays.
susceptible landscape plants.
body with a dark head and the legs on • Japanese beetle traps can
the thorax are well developed. Normally capture many adults have
Description of the the body curves into a “C-shape”.
never been shown to reduce
Japanese Beetle These features are also typical of
damage to nearby plants.
The adult Japanese beetle has an other white grubs found in association
oval form is about 7/16-inch in length. It with turfgrass in Colorado, such as • Japanese beetle larvae can
is generally metallic green with coppery- masked chafers and May/June beetles. be controlled with certain
brown wing covers, which do not quite (Extension fact sheet 5.516, Billbugs insecticides or by insect
cover the tip of the abdomen. Along the and White Grubs discusses white grubs parasitic nematodes.
sides are five patches of whitish hairs. of turfgrass in more detail.) Japanese
The antennae are clubbed at the end beetle larvae are slightly smaller than
and may spread to a fan-like form. . these other species when full grown but
Japanese beetle larvae are a type they are best distinguished by closely
of white grub that feeds on the roots examining the pattern of hairs on the
of grasses. They have a creamy white hind end of the abdomen (‘rastral
pattern’), which forms a distinctive
V-shape.
Japanese Beetle Damage
Japanese beetle can be damaging
to plants in both the adult and larval
stages. However the type of injuries
produced by adults and larvae are very
different.
Injury by the adults is more obvious
and is usually the primary concern in
Figure 1. Rose blossoms are one of the most Colorado. Adults feed on leaves, buds
highly favored foods of Japanese beetles.
© Colorado State University
and flowers of many common garden Extension. 5/07. Revised 3/18.
and landscape plants (Table 1). On extension.colostate.edu
leaves feeding is usually restricted to
*
W. Cranshaw Colorado State University Extension the softer tissues between the larger leaf
entomology specialist, and professor, bioagricultural veins, which results in a characteristic
sciences and pest management. 3/2018
Table 1. Some plants that are most commonly
damaged by Japanese beetle adults.
Virginia creeper* Grape
Rose** Linden*
Silver lace (Polygonum aubertii)**
Gaura**
Rose of Sharon** Hollyhock*
Raspberry* Crabapples (some)
Japanese maple Peking cotoneaster
Beans (edamame) Basil (green)
Figure 3. White grubs (larvae) of the Japanese
beetle. Photograph courtesy of David Shetlar,
Plants that are in flower during part of the time
the Ohio State University.
when Japanese beetle adult are present are
indicated by a single asterisk *. Plants that may
be blooming the entire time when Japanese
beetles are present on the plant are indicated by
Figure 6.. White grubs feed on the roots of
two asterisks **. grasses. Photograph courtesy of David Shetlar,
the Ohio State University.
established, adding to the damage
done by native white grubs present
symptoms of injury may be present
in Colorado turfgrass (e.g., masked
at this time, with damaged grass
chafers, May/June beetles). appearing drought stressed.
Larvae continue to feed until soil
Japanese Beetle Life temperatures drop to about 60oF at
Figure 4. The rastral pattern that is distinctive which time the larvae move deeper
for white grubs of the Japanese beetle. The History in the soil where they remain through
rastral pattern is located on the underside of Japanese beetle has a one year
the tip of the abdomen. Photograph courtesy of
winter. All activity ceases when soil
David Shetlar, the Ohio State University. life cycle. Adults may begin to temperatures drop below 50oF. Activity
emerge from the soil in early June and resumes as soils warm in spring and,
are usually most abundant in early after a feeding period of about 4-6
summer - from late June through early weeks, the larvae form an earthen cell
August. However, some adults may be and pupate. A few weeks later the
found into September. pupal stage is completed and the new
As adults, Japanese beetles can adults emerge.
be found feeding and mating on
foliage and flowers of their host plants.
Periodically, mated females will move Control of Adult
in late afternoon to areas of turfgrass to Japanese Beetles
lay eggs. They seek areas where soil is Japanese Beetle Trapping. Traps are
Figure 5. Japanese beetles that feed on leaves suitably moist and then dig 2-3 inches
produce a characteristic skeletonizing pattern. available that can capture Japanese
where they will lay a small cluster of beetle adults. These typically have a
feeding pattern known and described eggs among the plant roots. They vane of yellow panels at the top with
as “skeletonizing”. More generalized subsequently emerge and will resume a funnel underneath into which the
ragged feeding occurs on softer feeding on host plants, returning to beetles fall after impacting the panels.
tissues, notably flower petals; rose turfgrass later to lay more eggs. A total A lure of floral-based compounds is
flowers are particularly susceptible of 40-60 eggs may be laid by each used that is highly attractive to adults.
to Japanese beetle injury. Damage Japanese beetle female during the
on individual plants may be patchy, course of her 4-8 week life span.
concentrated where aggregations of Upon hatching from the eggs
feeding beetles occur. the grubs (larvae) seek out nearby
Japanese beetle larvae feed on plant roots and feed. During the
roots of grasses, in a manner similar time Japanese beetles are in the
to other turf damaging white grubs. egg and earliest grub stage they are
These injuries produce root pruning quite sensitive to drying and may
that limit the plant’s ability to acquire die if soils temporarily dry during Figure 7.. The life stages of the Japanese
water. Damaged areas of turfgrass are this period. Later stage larvae are beetle. From left to right: egg, larva (stage I),
more susceptible to water stresses and less sensitive to drying. Japanese larva (stage II), larva (stage III), pupa, adult.
Photograph courtesy of David Shetlar, the Ohio
severely pruned roots can lead to plant beetle larvae become nearly full-size State University.
death by drought. It is likely that there by early September and their rapid
will be increasing turfgrass damage development during late summer can
in areas where this species becomes cause extensive root pruning. Surface
can be particularly productive. The Some insecticides, which are less
regular removal of beetles prevents toxic to bees or persist for only a
the feeding damage produced by short period, can be used on plants
the beetles, which can reduce the that are in flower if applications are
production of chemicals produced by made during times of the day–early
wounded plants that are attractive to morning, dusk–when bees are not
the adult beetles. active and visiting plants. Examples
Insecticides.There are several include pyrethrins, azadirachtin, and
insecticides that can be used to help acetamiprid.
control damage by adult Japanese A couple of insecticides do not have
beetles (Table 2). These different restrictions for use on plants in bloom
insecticides vary considerably in because they have very little, if any,
features such as how long they can toxicity to bees. These include Bacillus
persist and control beetles, what thuringiensis var. galleriae (beetleJUS,
plants they can be used on, whether beetleGONE!) and chlorantraniliprole
they move systemically in the plant, (Acelepryn). At present (2018) the
and their hazard to desirable insects, former are only available through mail
notably pollinators. order and Acelepryn is only marketed
for commercial/agricultural uses.
Control of Japanese Beetle
Grubs in Lawns
Japanese beetle grubs can damage
Figure 8. Typical trap used to capture adults of turfgrass in the same manner as other
the Japanese beetle. turfgrass white grubs. (See Extension
Large numbers of adult beetles Fact Sheet 5.516, Billbugs and White
can be captured in these traps and Grubs). Some cultural practices can
they are useful for detecting the limit damage and applied chemical or
presence of Japanese beetle for biological controls may also be useful.
survey purposes. The traps also have However, control of Japanese beetle
some value in control where Japanese larvae in a yard will have very little, if
beetles are restricted to a very limited any, effect on the number of Japanese
location; mass beetle trapping was beetle adults feeding on trees, shrubs
a component of the Japanese beetle and garden plants. The insect is highly
eradication in Palisade, CO. mobile so that problems with adult
Unfortunately, Japanese beetle beetles typically involve insects that
traps are ineffective for control where have moved a considerable distance.
Japanese beetle is well established Cultural Controls. Mowing can affect
over a large area, common now in the susceptibility of lawns to grub
many Front Range locations. Repeated damage. This is because the size of
Figure 9. Hand picking can be a useful way to
trials have demonstrated that use reduce damage by Japanese beetle.
the root mass increases along with
of such traps does not reduce the mowing height. Therefore, turfgrass
If Japanese beetles are damaging that is mowed higher and has a larger
number of beetles damaging nearby flowering plants, this last feature, the
vegetation. Furthermore, the use of amount of roots can better tolerate root
potential for hazard to pollinators, is damage that does occur. Conversely,
Japanese beetle traps often increases very important in determining what
damage by Japanese beetles by lawns mowed shorter will have a
kinds of insecticides can be used. ) smaller mass of roots and plants
drawing into the vicinity larger Insecticides that are highly toxic to
numbers of beetles than are captured become more susceptible to grub
bees and can persist long enough to damage.
in the traps. Because of this Japanese kill insects for days are hazardous to
beetle traps are not recommended for Watering can have several effects.
pollinating insects that visit the flowers. Japanese beetle eggs and the tiny early
Japanese beetle control. These include products with the
Hand picking. Hand picking beetles stage larvae are very susceptible to
active ingredients carbaryl, bifenthrin, drying. If the top couple of inches of
can sometimes be effectively beta-cyfluthrin, lambda-cyhalothrin,
employed in small plantings. soil in a lawn can be allowed to dry a
permethrin, and imidacloprid. These bit during the time eggs are being laid
The beetles are easily picked or insecticides normally have label
dislodged; shaking infested plants and hatching - July and early August -
instructions to prohibit their use when then many may be killed. Since higher
over a collecting container in early there are flowers in bloom that are
morning when temperatures are cool temperatures during this period tend to
attractive to bees. make plants be more susceptible to water
stress, growing lawns in a manner that
promotes deep root growth can allow
the lawn to be more tolerant of some soil
drying. One way that this can be achieved
is through deep, but less frequent,
irrigation during spring.
If grubs have already caused some
root injury, usually in late August and
September, then watering may need to
be increased a bit to keep soils moist
enough to promote regrowth of roots.
Anything that can improve growing Figure 10. Bees and other pollinating insects Figure 11. A white grub killed by the
may be visiting flowers on which Japanese nematode Heterorhabitis bacteriophora. Grubs
conditions-watering, fertilization, core beetles are feeding. In these situations there that are infected by this nematode turn a
aeration, mowing-can allow turfgrass must be special care when using insecticides reddish-brown color. Photograph courtesy of
plants to better tolerate root damage to avoid killing pollinators. David Shetlar, the Ohio State University.
white grubs produce.
Biological Controls. Soil drench will not produce immediate reductions Plus Granules) has a more limited
applications of certain kinds of insect in number of Japanese beetles; if an use for control of Japanese beetle
parasitic nematodes can provide application of milky spore is able to grubs. This insecticide is able to move
good control of Japanese beetle result in successfully infecting some quickly into the soil and can provide
grubs in lawns. (These organisms are grubs, then milky spore will continue fairly rapid kill compared to other
discussed in more detail in Extension to reproduce and spread on its own. treatments. However, it very rapidly
Fact Sheet 5.573, Insect Parasitic In areas of the eastern United States, degrades in soil, particularly high pH
Nematodes). Specifically effective where milky spore has long been soils. This insecticide is sometimes
are certain nematodes in the genus widespread, it annually infects a small used for “rescue treatments”, applied
Heterorhabditis (e.g., Heterorhabditis number of grubs, resulting in some to grubs present later in summer after
bacteriophora, H. megadis) and reduction of the Japanese beetle all eggs have hatched.
several biological control suppliers will populations (less than 5%). There can be some risk to
provide these organisms. Applications Insecticides for grub control. pollinators if insecticides are applied
of Heterorhabditis nematodes are Several insecticides (Table 3) are to lawns that have flowering plants
made as a soil drench, preferably presently available that can provide attractive to bees. If flowering plants
during cool, overcast periods, and excellent control of Japanese beetle are present in a site that is to receive
must be immediately watered into grubs in lawns. Most commonly an insecticide application it should be
the turfgrass. They should be applied available are insecticides that are mowed immediately before treatment
when Japanese beetle larvae are applied preventively to kill young grub to remove the attractive blooms.
present and active. stages. These include imidacloprid
A new product being marketed (Merit, Zenith, several retail products),
for control of white grubs is a strain chlorantraniprole (Acelepryn, Scott’s
(galleriae) of the bacterium Bacillus GrubEx), and chlothianidin (Arena),
thuringiensis that specifically affects all of which can provide control of
adults and larvae of scarab beetles Japanese beetle larvae over an
such as Japanese beetle. It is extended period (several weeks-
presently being sold as grubGONE! months). Applications of these types
and is best applied against small of products are best made just before
larvae in early-midsummer. eggs hatch or shortly after this time
Another biological control that has (typically mid-June to early July).
received considerable past attention Rates of use are dependent on
for Japanese beetle control is milky time of application with lower rates
spore (Paenibacillus popilliae), a being adequate when applied against
bacterium that produces “milky younger larvae in early summer.
disease” in Japanese beetle grubs. Higher rates are needed when late
(The currently available formulation is stage larvae are present. Control will
sold under the trade name St. Gabriels’ diminish if applications are made
Organics Milky Spore Powder.) Milky later in the season, when grubs are
spore is applied to turfgrass areas large, and these products will often
where Japanese beetle grubs are give disappointing results when used
active and may infect some of the in “rescue” treatments for existing
grubs, producing a chronic infection infestations in advanced stages.
that reduces survival and reproduction. The insecticide trichlorfon (Dylox,
Applications of milky spore powder Bayer Advanced 24 Hour Grub Killer
Table 2. Insecticide options for control of adult Japanese beetles on leaves and flowers
Common Name Trade Names Persistence of control Labeled Uses on Food Pollinator Hazards, Cautions
(Insecticide Class) Crops
acetamiprid
(neonicotinoid) Tristar, Ortho Flower, Fruit, and Vegetable Insect Killer Moderate persistence; Label allows use on some Can be used on plants that are in blossom
provides control of damage for fruits and vegetables. but cannot be applied at times when bees
days-week. Moves systemically are visiting (i.e., dusk, dawn applications
within plants. allowed).
azadirachtin BioNeem, Azasol, AzaGuard, AzaMax, others Short persistence; provides Uses allowed for essentially Hazardous to bees if directly sprayed. Can
(unspecified, control of damage for a couple all food crops. be used on plants that are in blossom but
botanical origin) of days. cannot be applied at times when bees
are visiting (i.e., dusk, dawn applications
allowed).
Bacillus thuringiensis beetleGONE!, beetleJUS! Persistence is 2-3 days. Acts Many food crop uses are Very low hazard to bees. Can be applied to
var. galleriae as stomach poison that causes allowed. plants that are in flower and are being visited
(microbial) beetles to stop feeding very by pollinators.
shortly (hours) after it is eaten.
Beetles may not die for several
days.
bifenthrin (pyrethroid) Ortho Max Insect Killer for Lawns and Gardens, Persistence moderate-long; No food crop uses are High hazard and can kill bees for days after
Talstar, Onyx provides control of damage for allowed. application. Cannot be used on plants bees
about a week. visit that are in bloom.
carbaryl (carbamate) Sevin, Carbaryl Persistence moderate-long; Label allows many food High hazard and can kill bees for days after
provides control of damage for crop uses. application. Cannot be used on plants bees
about a week. visit that are in bloom.
chlorantraniliprole Acelepryn SC Persistence moderate-long; No food crop uses are Very low hazard to bees. Can be applied to
(diamide) provides control of damage for allowed. plants that are in flower and are being visited
about a week. by pollinators. Not marketed for retail.
beta-cyfluthrin Tempo, Bayer Advanced Rose and Flower Insect Killer Moderate persistence; Some uses allowed for High hazard and can kill bees for a day or two
(pyrethroid) (with imidacloprid), Bayer Advanced Vegetable and provides control of damage for products that solely contain after application. Cannot be used on plants
Garden Insect Spray days-week. beta-cyfluthrin; formulations bees visit that are in bloom.
with imidacloprid do not
allow food crop uses.
gamma-cyhalothrin Triazicide Insect Killer for Lawns and Landscapes Persistence moderate; Labeled for use on many High hazard and can kill bees for days after
(pyrethroid) provides control of damage for vegetable and most fruit application. Cannot be used on plants bees
days-week. crops. visit that are in bloom.
imidacloprid Merit, Mallet, Zenith, Bonide Systemic Insect Spray, Moderate persistence; Variable, depending on High hazard to bees. Do not apply when
(neonicotinoid) Bayer Advanced 2-in-1 Systemic Rose & Flower sprays can provide control of formulation. Many products bees are foraging. Do not apply to plants that
Care, Bayer Advanced Tree & Shrub Protect & Feed damage for days-week. Moves that have imidacloprid as are flowering. Only apply after all petals have
(with chlothianidan), Bayer Advanced Fruit, Citrus systemically within plants. the sole active ingredient fallen off.
and Vegetable Insect Killer Hi-Yield Systemic Insect also allow use on some
Granules, Ortho Bug B Gon Year-Long Tree & Shrub fruits and vegetables.
Insect Control, ferti-lome Tree & Shrub Systemic
Insect Drench, others
permethrin Bonide Eight Insect Control Vegetable, Fruit & Flower; Short to moderate persistence. Label uses include most High hazard and can kill bees for a day or two
(pyrethroid) Bayer Advanced Complete Insect Dust for Gardens; Provides control of injury for a vegetable and many fruit after application. Cannot be used on plants
Ace House & Garden Bug Killer2, Astro, Permethrin, few days. crops. bees visit that are in bloom.
others
pyrethrins (botanical) Pyrenone, Pyganic, many retail Very short persistence; Uses allowed for essentially all food crops.
formulations provides control for a day
or two.
Table 3. Insecticide and Biological Control Options for Control of Japanese Beetle Larvae (White Grubs) in Lawns
Common Name Trade Names Trade Names (Retail) Insecticide Class Comments
(Commercial)
imidacloprid Merit, Mallet, Zenith, Hi-Yield Grub Free neonicotinoid Has moderate-long persistence.
others Zone II, Bayer Applications are most effective when made
Advanced Complete in June through early August. Fairly fast
Insect Killer for Soil (a couple of weeks) in providing control
& Turf (with beta- of grubs following application. Moves
cyfluthrin), Bayer systemically in plants. Hazardous to bees if
Advanced Season- applied when flowering plants in lawns are
Long Grub Control, present during application
Bonide Grub Beater
chlothianidan Arena None neonicotinoid Has long persistence. Can provide control
if applied from May into August. Fairly fast
(a couple of weeks) in providing control
of grubs following application. Moves
systemically in plants. Hazardous to bees if
applied when flowering plants in lawns are
present during application.
chlorantraniliprole Acelepryn SC, GrubEx diamide Has very long persistence but moves
Acelepryn G relatively slowly into soil. Best applied
in May/June; some control possible with
applications made in April or early August.
Fairly slow (weeks) in providing control
after application. Has some ability to move
systemically in plants. Very low hazard to
bees. Very low hazard to humans, pets.
trichlorfon Dylox Bayer Advanced 24 organophosphate Very short persistence but is fast acting.
Hour Grub Killer Plus Used to control existing problems with white
Granules grubs. Must be watered in immediately after
application. Breakdown is very rapid (days),
particularly in high pH soils. Fairly low hazard
to bees; where flowering weeds are present
mowing before application greatly reduces
risk to pollinators.
Bacillus thuringiensis None grubGONE! microbial (bacterium) Short residual activity. Best used after
var. galleriae most eggs have hatched and grubs are still
in young stages (mid-July through mid-
August). Kills larvae through disruption of
midgut. A very new product with little data
yet available to make efficacy comparisons
with other products.
Heterorhabditis HeteroMask, Grub- HeteroMask, Grub- insect parasitic hese are living organisms (minute
bacteriophora Away, BioStrike Hb, Away, BioStrike Hb, nematode nematodes/roundworms) that are applied to
GrubStake Hb, others GrubStake Hb, others (entomopathogenic soil as a drench and watered immediately.
nematode) Treatments should be made when grubs
are present and soil temperatures are
warm. Control is usually rapid (days
after treatment) and infected grubs turn a
reddish-brown color.
Milky spore None St. Gabriel Organics microbial (bacterium) Not a product that can be expected to
(Paenibacillus Milky Spore provide any noticeable control for years.
popilliae) Milky spore will usually spread on its own
over time once applied to a turfgrass site.
Experience in areas where this organism
has long been present indicates it provides
modest effects, killing a small percentage
(
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