Japanese beetle resistant trees

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by Jessica Walliser June 16, 2014


Courtesy Marie Coleman/Flickr

One aspect of companion planting that can be quite useful in the vegetable patch is partnering plants in hopes of repelling certain pests. While many pest-deterring companion planting tactics have yet to be scientifically proven, there’s no doubt that several of them are quite effective in deterring certain pests in the garden, even if they’ve only been “proven” via hand-me-down knowledge. Even if a particular pest-deterring plant partnership doesn’t work in your garden, it certainly won’t cause it any harm.

Here are a handful of my favorite plants for discouraging pests in the vegetable garden to jumpstart your companion planting endeavors.

1. Basil
Among the most popular partnerships, basil and tomatoes go hand-in-hand—both on the plate and in the garden. Basil is said to repel whiteflies, spider mites and aphids on tomatoes. Planting basil around young tomato plants can confuse adult hornworm moths, preventing them from finding the plants and laying their eggs.

2. Dill
Dill helps deter squash bugs, so plant it among your squash plants to keep your crop safe. It also helps repel adult cabbageworms when planted among cabbage and other cole crops. The heavily scented leaves of dill may repel other insects, as well, or simply mask the scent of the host plant.

3. Nasturtiums
Many gardeners find success planting nasturtiums among cucumber vines to repel the cucumber beetles that feed on cucumber leaves and flowers, and transmit bacterial wilt. Some gardeners also report that vining nasturtium varieties help deter squash bugs when planted among winter squash.

4. Onions
The bold odor of onions may actually repel pests or confuse them by masking the fragrance of their preferred host plants. Either way, onions in the cucumber patch can scare off cucumber beetles, and planting them between carrot rows repels adult carrot root maggot flies. Circling a row of onions around tomato plants is also said to help repel sap-sucking aphids.

5. Garlic
The scent of this aromatic is said to repel aphids in the lettuce patch, as well as send Japanese beetles packing when planted around blueberries, roses, raspberries and other susceptible crops. Garlic plants are also used to keep spider mites away from phlox and other vulnerable perennials.

6. Tomatoes
With strongly scented foliage of their own, many gardeners use tomatoes to protect their cabbage and broccoli crop from diamond back moth larvae. The adult moths are less likely to lay eggs on cole crops planted between and beneath tomato plants.

7. Catnip (Nepeta spp.)
Plant this perennial member of the mint family between rows of plants susceptible to flea beetle damage, such as radish and eggplants, as the adult beetles are repelled by the fragrance.

8. Calamint
Another member of the mint family, this perennial is reportedly quite adept at deterring cabbageworms, cabbage loopers and diamondback moth larvae on cole crops. Plant a few calamint plants near these crops, but be careful to deadhead the flowers before they drop seed to prevent it from taking over the garden.

9. Tansy
Some gardeners use this herb to keep Japanese beetles at bay, planting it among brambles, roses and other plants favored by adult Japanese beetles. Tansy’s strong scent is said to either deter them directly or make it difficult for the beetles to hone in on their host plant.

10. Marigolds
Tall marigold varieties, such as African marigolds (Tagetes erecta), are used by some gardeners to deter tomato and tobacco hornworms. When planted in between tomato plants, they are thought to confuse the adult hornworm moths and keep them at bay.

11. Borage
Used by gardeners for centuries to discourage hornworms on tomatoes and cabbageworms on cole crops, borage is a beautiful addition to the garden. Easily grown from seed, this herb can be readily grown around susceptible plants. It’s also great at supporting Honey bees and other pollinators.

12. Lavender
When grown among lettuce and other leaf crops, the heavily scented leaves of lavender dissuade both whiteflies and aphids.

13. Parsley
Planting parsley in the asparagus bed may send asparagus beetles packing, particularly early in the season when the spears are just emerging.

14. Castor Oil Plant
Although it should be grown with care (all parts—especially the beans—are extremely poisonous to humans and animals when ingested), the castor oil plant is proven to keep moles and voles at bay. Planted around the perimeter of the garden, it keeps voles from moving in. Some commercial mole and vole repellents are even made from the castor oil plant because it works so well.

Get more help battling your garden’s bad bugs:

  • 13 Headache-Inducing Garden Pests and How to Control Them
  • Keep Garden Pests Away With Decoy Crops
  • Pest Patrol: Integrated Pest Management
  • Pests and High Tunnels
  • 2 Tools to Outsmart Garden Pests

About the Author: Horticulturalist Jessica Walliser is the author of Good Bug, Bad Bug: Who’s Who, What They Do and How to Manage Them Organically (St. Lynn’s Press, 2008) and co-host of Pittsburgh’s top-rated gardening radio program, The Organic Gardeners, on KDKA Radio. Learn more helpful gardening tips in her blog, “Dirt on Gardening.”

Japanese Beetle Problem? Try Geraniums and Milky Spore

One of the most notorious garden pests of the summer is the much reviled Japanese Beetle.

Adult Japanese Beetle

Popilla japonica, a stowaway from Japan, was accidentally introduced into the U.S. in 1916, and when it encountered no natural predators, populations grew to overwhelming proportions inside of 50 years. They became and remain an annual nightmare for gardeners and farmers. Anyone who’s ever been subject to visits by these creatures for a few weeks in the summer knows exactly what I’m talking about. In a bad year, they’re seemingly everywhere, eating their way through plant leaves and flowers, and leaving holes in fruit. In fact, Japanese Beetles feed on over 300 plants in 80 families and are very difficult to get rid of.

Your lawn is a Japanese Beetle’s winter home

If you’re reading this between August and May, our flying friends are living in your yard’s soil right now. Japanese Beetles in larval stage, called grubs, live less than a foot beneath your lawn, and as the weather warms, slowly work their way towards the surface, where they feed on the roots of your grass for 4-6 weeks as they grow into adults. Unchecked, they can kill wide swaths of lawn, as the weakened grass loses its ability to survive heat stress. When adults, they emerge from their winter home to attack a wide assortment of plants and trees, including roses, raspberries, pear trees, maple trees, dahlias, grapes, apple trees, hollyhocks, lilacs, and holly. And then there’s the THUNK sound made by their heavy green metallic shells as they smash into and bounce off windows and aluminum siding. They’re like clumsy, drunken visitors from another planet. Fortunately, Japanese Beetles have a short, one generation life cycle.

Why did their populations grow so quickly? The American lawn. Since we have such an addiction to well watered turf grasses, the Japanese beetle larva has plenty of food and lodging over winter. Big lawns aren’t common in their original home of Japan – or many other places in the world for that matter – and providing this undisturbed winter shelter encourages a high survival rate.

How to get rid of Japanese Beetles

As always, insecticides are definitely not the way to rid your plants of these pests. Garden centers will usually recommend products containing carbaryl (like Sevin, Adios, Carbamec, and Slam), but carbaryl is incredibly poisonous for birds, bees, pets, anything living in your soil, local waterways, fish, and YOU (it’s notorious for causing skin burns and irritated eyes).

For this season, a fast way to get rid of Japanese Beetles is with Diatomaceous Earth which you can read about here.

But there is hope. as animals like skunks, shrews, moles, and birds feed on the grubs. In early spring you may find small holes in your lawn, made by wildlife searching for the young beetles – they’re apparently a pretty tasty morsel. Unfortunately, there are few natural predators for the adult beetles, which is why they remain prolific.

Milky Spore Powder

The gold standard organic control for Japanese Beetle grubs is Milky Spore powder, which contains a very specific bacterial spore, Bacillus popillae. When ingested by the grubs, the bacteria turns their internal fluids milky white, hence the name. The grubs die of this disease, and when they do, more milky spore is produced, which creates a self-perpetuating cycle. Milky Spore lasts for many years in your soil, and it’s completely safe for wildlife, pets and you. An application on your lawn in early fall, followed by a good watering in is all that’s needed (grubs are more likely to ingest the spores in fall when they’re feeding heavily).

Milky Spore powder may be able to rid your lawn of grubs, but unfortunately, there are more of these sinister flying marauders hiding underneath your neighbors’ lawn. When these grubs mature into adults, they’ll fly right over and start feasting on your favorite rose bush. So besides the milky spore, you also need some protection against the adult stage beetles.

Milky Spore powder is only effective on grubs July-September, according to the University Of Minnesota Extension. Outside of that window, grubs are too large to be affected by the bacteria.

Buy on Amazon: Milky Spore Powder

I do not recommend using Japanese Beetle traps. Sure, they catch tons of beetles. But since the bait is a pheromone, the beetles are attracted from up to 1 mile away. Not only are you catching the adult beetles from around your home, but you’re catching the entire neighborhood’s. And those beetles who flew in from down the street and didn’t get caught in the trap feast on your plants and trees. I’ve had better success deterring Japanese Beetles without the traps.

Life stages of the Japanese Beetle

Use your hands

Japanese Beetles are slow and clumsy, so picking them off your plants or shooting them with a soap and water spray solution is very effective. When they fall, you can easily crush them with your hand or foot.

Plant Geraniums

In 1929, it was discovered that a natural control for adult beetles is, believe it or not, geraniums. The beetles feed on the geranium leaves and flowers, which puts them into a narcotic state for 12-18 hours. They lay on their backs while enjoying their altered state, which makes them susceptible to predators and easy for gardeners to collect and crush. Some beetles ingest the irresistible geranium leaves to such a degree and so often that they die from it.

But don’t interplant geraniums around your roses, thinking that this will deter the pests. Because Japanese Beetles love geraniums so much, interplanting will create the opposite effect and attract so many beetles that your roses will become infested. Plant a patch of geraniums in a sunny place far away from the plants you want to protect, as it’s believed that the sun has an intensifying effect on the narcotic substance in the geranium leaves.

Insect Controls (parasites)

Most adult Japanese Beetle control is performed by other insects and the USDA considers the spring Tiphia wasp the most effective. This is another reason not to use insecticides, as you’ll kill the “beneficial” insects too. After mating, female spring Tiphia wasps burrow into the soil, searching for grubs. When the female finds one, she paralyzes it while she attaches one of her eggs to its abdomen. The beetle grub serves as a food source for the egg and after it hatches, the larva continues to feed on the grub until the grub dies. The female wasp can normally parasitize 1 to 2 grubs daily in this manner, and can lay a total of between 40 and 70 eggs over her lifespan of about 30 days.

Fortunately, the spring Tiphia wasp is not aggressive towards humans and will not normally sting people, since they’re only 1 cm – 2 cm long. Tulip Poplar, Choke Cherry, Norway Maple, American Elm, Forsythia, Firethorn, and Pine trees are great host plants for these wasps. Plant one of these on your property if Japanese Beetles are a consistent problem.

Winsome flies actually lay eggs in adult Japanese beetles. When the larvae hatch, they burrow deep into the beetle and begin feeding. This sends the beetle into a frenzy and it buries itself in the soil where the larva continues to feed until the beetle dies. Then the fly overwinters in the hollowed beetle shell. The adult Winsome fly emerges the following spring to find more Japanese Beetles to lay eggs on.

I almost feel bad for the Japanese Beetles after writing this last part. Almost.

How to Protect Your Trees and Shrubs From Japanese Beetle Damage

Weeding

Japanese beetles like dining on weeds along with other plants, so keep the garden tidy. It eliminates beetle food and hiding places as well.

Pesticide Application

Japanese beetles are persistent, so an effective, trusted pesticide is an important part of any control plan. Highly effective Sevin® brand garden insecticides from GardenTech are tough on beetles, but gentle on gardens. You can choose the product type that works best for you.

Sevin® Insect Killer Ready To Use, in a convenient spray bottle, kills Japanese beetles and more than 500 types of insect pests by contact. Then, it keeps on working and protecting your plants against pests for up to three months. For hose-end spraying, get the same highly effective, long-lasting protection with Sevin® Insect Killer Ready To Spray; use Sevin® Insect Killer Concentrate for larger areas and backpack or tank sprayers.

A thin, even layer of Sevin®-5 Ready-To-Use 5% Dust treats Japanese beetles on ornamental shrubs and small trees, working best at chest height or lower. Leave taller plants to liquid Sevin® products. For trees over 10 feet tall or plants you can’t spray effectively because of their size, call in a horticulture professional to apply the pesticide.

To fight Japanese beetles at the grub stage as well as adults, Sevin® Insect Killer Granules works above and below the surface to kill beetle larvae along with more than 100 other insect pests. Applied according to directions, the granules kill pests by contact and protect your lawn, edible and ornamental gardens, and other areas around your home for up to three months.

Japanese beetles put up a good fight in your garden, but GardenTech® and Sevin® brands are here to help. With preparation, regular tending and highly effective products, you can prevent these pests from damaging your trees and shrubs, and get back to enjoying your landscape.

Total Time to Keep Japanese Beetles under Control: 1-2 hours per week during spring

Effort rating: 2 – Easy Does It

Time breakdown (depending on the number of plants affected):

  • Locate beetle infestation areas: 15 minutes
  • Handpick beetles from highly concentrated infestation areas: 15-45 minutes
  • Apply control product: 30-60 minutes

Always read product labels thoroughly and follow instructions carefully, including guidelines for application frequency and pre-harvest intervals (PHI) on edible crops.

GardenTech is a registered trademark of Gulfstream Home and Garden, Inc.

Sevin is a registered trademark of Tessenderlo Kerley, Inc.

Sources:

1. USDA Animal and Plant Health, “Managing the Japanese Beetle: A Homeowner’s Handbook,” United States Department of Agriculture, August 2015.

3. Vera Krischik and Doree Maser, “Japanese Beetle Management in Minnesota,” University of Minnesota Extension, 2011.

4. W. Cranshaw, “Japanese Beetle,” Colorado State University Extension, May 2013.

Plants That Japanese Beetles Don’t Like

Japanese beetles are voracious eaters and can completely decimate a garden if left to their own devices. To minimize or even prevent the damage these creepy-crawlies can do, try planting plants that deter them, or that they don’t feed on.

Plants that deter Japanese Beetles

It may seem incredible, but there actually are plants that Japanese Beetles avoid. These plants typically have a strong scent and don’t taste good to the insect. Some of the plants that deter Japanese Beetles are:

  • Catnip
  • Larkspur
  • Onions
  • Leeks
  • Chives
  • GarlicWhite Chrysanthemum
  • White Geraniums
  • Marigolds
  • Tansy

Plants That Don’t Attract Japanese Beetles

These are plants that just don’t interest Japanese beetles very much. While these plants can occasionally suffer from minor Japanese beetle damage, the nice thing about them is that the Japanese beetles will quickly lose interest in them, since they’re not as tasty to them as some other plants are. Japanese beetle resistant plants include:

  • American Sweet Gum
  • American Elder
  • Begonias
  • Black Oak
  • Boxelder
  • Boxwood
  • Caladiums
  • Common lilac
  • Common Pear
  • Tuliptree
  • White Oak
  • White Poplar
  • Dusty Miller
  • Euonymus
  • Flowering Dogwood
  • Forsythia
  • Green Ash
  • Holly
  • Hydrangea
  • Hickory
  • Junipers
  • Magnolia
  • Persimmon
  • Pines
  • Red Maple
  • Red Mulberry
  • Red Oak
  • Scarlet Oak
  • White Ash
  • Shagbark

With a combination of the above plants, you should be able to stave off, or at least minimize, the effects of Japanese beetles in your garden.

Dealing with Japanese Beetles

Every summer, questions pour in to us regarding the Japanese Beetles that are voraciously devouring people’s flowers and plants. It’s quite obvious these little buggers are the culprit. Their ¼” long bodies are easy to spot and since they are very slow moving, you’ll likely catch them in the act. Their shiny metallic green and copper shells glisten in the sun like rare jewels but beauty can be deceiving! They don’t seem to care a bit that they are destroying our favorite roses, hibiscus and clematis flowers.

Japanese Beetles are a major summer pest throughout the Central, Midwestern and Northeastern United States and Canada. They live as grubs in your soil from fall through winter, then emerge as beetles between early June and late August. Your local extension agent will have more specific information for the timing of Japanese Beetles in your area. Once they emerge as beetles, they chew large holes in flowers and foliage to the point where they will even eat every last leaf off of the plants they love. Members of the Rose family are their favorite targets.

As is the case with most pests, there are a variety of ways to try to control Japanese Beetles. Focusing on prevention is key since their hard shells make them tougher to kill once they have turned into beetles. Here are a few things you can do to control Japanese Beetles in your garden.

Prevention
Before Japanese Beetles emerge, they are grubs that live under your lawn and in your garden beds. So prevention means getting to the grubs before they can grow up into beetles and spread all over your garden. There are lots of options for controlling grubs. The following can be purchased at garden centers or online.

  • Grub-eating Nematodes (Heterorhabditis bacteriophora) – These beneficial nematodes find grubs in the soil and kill them.
  • Bt (Bacillus thuringiensis) – Bt is a naturally occurring soil bacteria that eats Japanese Beetle grubs before they can develop into beetles.
  • Milky Spore (Bacillus papillae)—This bacterium takes 2-4 years to become established in the landscape but then offers continuous protection from Japanese Beetle grubs.

Hand Picking
This method is not for the squeamish! Most people don’t want to touch bugs, but Japanese Beetles do not bite and you can pick them off plants and either bag them or drop them into a bucket of soapy water to get rid of them. It is easiest to do this early in the morning before the beetles wake up and start moving.

Trapping
There are traps you can buy at home improvement stores which are made especially for Japanese Beetles. The way they work is by luring the pests into a small container from which they cannot escape. This can work to help reduce the beetle population, but don’t leave the trap out all the time (maybe just a day or two a week) as it will attract all the local bugs to your garden and that can be a LOT of beetles. Since the beetles may feed on nearby plants before entering the trap, do not set the trap out near your favorite plant. Instead, place the trap at the edge of your yard away from the plants the beetles may damage. Make it a neighborhood effort as traps become more effective if there are many scattered throughout the area.

Chemicals
Select chemicals can be effective at controlling Japanese Beetles. Least toxic to humans and pets are the Pyrethrin class of insecticides which are safe to use on vegetables, grapes, raspberries, flowers, roses, trees and shrubs but can be very bad for fish, so avoid using them around ponds. Another low toxicity control method is applying Neem Oil as a spray as soon as the beetles appear in your garden. Neem Oil can help control Japanese Beetles, Cucumber Beetles, Flea Beetles, Cabbageworms, and Colorado Potato Beetles.

Planting Resistant Plants
Japanese Beetles seem to try a taste of just about everything in the garden, but there are actually a select group of woody and herbaceous plants that they typically leave alone. Consider this list when adding new plants to your garden if you are plagued by Japanese Beetles.

RESISTANT to Japanese Beetles

VULNERABLE to Damage from Japanese Beetles

Trees & Shrubs

Herbaceous Plants

Trees & Shrubs

Herbaceous Plants

Arborvitae

Ash

Boxwood

Burning Bush

Dogwood

Forsythia

Hemlock

Hickory

Holly

Juniper

Lilac

Magnolia

Northern Red Oak

Pine

Redbud

Red Maple

Spruce

Sweetgum

Tulip Poplar

Yew

Ageratum

Begonia

California poppy

Columbine

Coral Bells

Coreopsis

Dusty Miller

Forget Me Not

Foxglove

Hosta

Impatiens

Lantana

Larkspur

Lily of the Valley

Moss Rose

Nasturtium

Pachysandra

Pansy & Viola

Poppy

Showy Sedum

American Mtn Ash

Apple & Crabapple

Beech

Birch

Black Walnut

Crape Myrtle

Hawthorn

Horse-chestnut

Japanese Maple

Larch

Linden

Lombardy Poplar

Norway Maple

Plum, Apricot,

Cherry, Peach

Pin Oak

Rose of Sharon

Sassafras

Summersweet

Virginia Creeper

Willow

Asparagus

Cardinal Flower

Clematis

Common Mallow

Daisy

Dahlia

Evening Primrose

Gladiolus

Grape

Hibiscus

Hollyhock

Lily

Morning glory

Peony

Red Raspberry

Rhubarb

Rose

Soybean

Sunflower

Sweet Corn

Zinnia

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Japanese Beetles in the Urban Landscape

ENTFACT-451: Japanese Beetles in the Urban Landscape | Download PDF

by D.A. Potter, M.F. Potter, and L.H. Townsend, Extension Entomologists
University of Kentucky College of Agriculture

The Japanese beetle is probably the most devastating pest of urban landscape plants in the eastern United States. Japanese beetles were first found in this country in 1916, after being accidentally introduced into New Jersey. Until that time, this insect was known to occur only in Japan where it is not a major pest.

The eastern US provided a favorable climate, large areas of turf and pasture grass for developing grubs, hundreds of species of plants on which adults could feed, and no effective natural enemies. The beetle thrived under these conditions and has steadily expanded its geographic range north to Ontario and Minnesota, west to Iowa, Missouri and Arkansas, and south to Georgia and Alabama.

The first Japanese beetles discovered in Kentucky were found on the southern outskirts of Louisville in 1937. Isolated infestations were treated with insecticides to delay spread of the beetle. During the 1950s and 1960s, beetle populations increased dramatically and spread in Kentucky and surrounding states. Today, the Japanese beetle infests all of the counties in Kentucky.

Leaves skeletonized by Japanese beetles

Description and Habits

Adult Japanese beetles are 7/16-inch long metallic green beetles with copper-brown wing covers. A row of white tufts (spots) of hair project from under the wing covers on each side of the body.

Adults emerge from the ground and begin feeding on plants in June. Activity is most intense over a 4 to 6 week period beginning in late June, after which the beetles gradually die off. Individual beetles live about 30 to 45 days.

Japanese beetles feed on about 300 species of plants, devouring leaves, flowers, and overripe or wounded fruit. They usually feed in groups, starting at the top of a plant and working downward. The beetles are most active on warm, sunny days, and prefer plants that are in direct sunlight. A single beetle does not eat much; it is group feeding by many beetles that results in severe damage.

Adults feed on the upper surface of foliage, chewing out tissue between the veins. This gives the leaf a lacelike or skeletonized appearance. Trees that have been severely injured appear to have been scorched by fire. Japanese beetles may completely consume rose petals and leaves with delicate veins. Odors emitted from beetle-damaged leaves seem to be an important factor in the aggregation of beetles on particular food plants.

Adult Japanese beetles are highly mobile and can infest new areas from several miles away. Usually, however, they make only short flights as they move about to feed or lay eggs.

Egg laying begins soon after the adults emerge from the ground and mate. Females leave plants in the afternoon, burrow 2 to 3 inches into the soil in a suitable area, and lay their eggs–a total of 40 to 60 during their life. The developing beetles spend the next 10 months in the soil as white grubs. The grubs grow quickly and by late August are almost full-sized (about 1 inch long). Grubs feed on the roots of turfgrasses and vegetable seedlings, doing best in good quality turf in home lawns, golf courses, parks, and cemeteries. However, they can survive in almost any soil in which plants can live.

Mid-summer rainfall and adequate soil moisture are needed to keep eggs and newly-hatched grubs from drying out. Females are attracted to moist, grassy areas to lay their eggs; thus, irrigated lawns and golf courses often have high grub populations, especially during otherwise dry summers. Older grubs are relatively drought resistant and will move deeper into the soil if conditions become very dry. Japanese beetle grubs can withstand high soil moisture, so excessive rainfall or heavy watering of lawns does not bother them.

As Japanese beetle grubs chew off grass roots, they reduce the ability of grass to take up enough water to withstand the stresses of hot, dry weather. As a result, large dead patches develop in the grub-infested areas. The damaged sod is not well-anchored and can be rolled back like a carpet to expose the grubs. If the damage is allowed to develop to this stage, it may be too late to save the turf. Early recognition of the problem can prevent this destruction.

Japanese beetles overwinter in the grub stage. When the soil cools to about 60°F in the fall, the grubs begin to move deeper. Most pass the winter 2 to 6 inches below the surface, although some may go as deep as 8 to 10 inches. They become inactive when soil temperature falls to about 50°F.

When soil temperature climbs above 50°F in the spring, the grubs begin to move up into the root zone. Following a feeding period of 4-6 weeks, the grubs pupate in an earthen cell and remain there until emerging as adults.

Adult Japanese beetles

Control

From a management standpoint, it is important to recognize that both the adults and grubs can cause damage. Moreover, since Japanese beetle adults are capable of flying in from other areas, controlling one life stage will not preclude potential problems with the other. Options for protecting trees, shrubs, and flowers from adult Japanese beetles are presented below. Control of the grub stage requires properly timed applications of a soil insecticide to infested turf. Diagnosis and control of white grubs in turf is discussed in a companion publication, Kentucky Cooperative Extension Service publications ENT-10, “Controlling White Grubs” and Entfact 441, “Insecticides for Controlling of White Grub in Kentucky Turfgrass.”

Plant Selection

Careful selection of plant species when replacing or adding to your landscape is the key to avoiding annual battles with Japanese beetles. Some species and cultivars are highly preferred by the adults and should be avoided where the beetle is abundant. Plants that are especially prone to damage include roses, grapes, lindens, sassafras, Norway maple, Japanese maple, purple-leaf plum, and others (Table 1). Many varieties of flowering crabapples are also severely attacked by the beetles, although some cultivars are resistant.

Roses are highly susceptible to Japanese beetles

Fortunately, many common trees and shrubs are much less attractive to Japanese beetles (Table 2). These differences in susceptibility should be considered when selecting plant species and cultivars for use in Japanese beetle-infested areas.

Japanese beetles are also fond of certain weeds and non-cultivated plants such as bracken, elder, multiflora rose, Indian mallow, poison ivy, smartweed, and wild grape. Elimination of these plants whenever practical destroys these continuous sources of infestation.

Although plant selection is important, other approaches must obviously be used to protect susceptible plants that are already established in landscapes.

Physical Removal and Exclusion

Removing beetles by hand may provide adequate protection for small plantings, especially when beetle numbers are low. The presence of beetles on a plant attracts more beetles. Thus, by not allowing beetles to accumulate, plants will be less attractive to other beetles.

One of the easiest ways to remove Japanese beetles from small plants is to shake them off early in the morning when the insects are sluggish. The beetles may be killed by shaking them into a bucket of soapy water. Highly valued plants such as roses can be protected by covering them with cheesecloth or other fine netting during the peak of beetle activity.

Chemical Control

Many insecticides are labeled for use against adult Japanese beetles. Examples include pyrethroid products such as cyfluthrin (Tempo, Bayer Advanced Lawn & Garden Multi-Insect Killer), bifenthrin (TalstarOne, Onyx), deltamethrin (Deltagard), lambda cyhalothrin (Scimitar, Spectracide Triazicide), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer) and permethrin (Spectracide Bug Stop Multi-Purpose Insect Control Concentrate and other brands). Carbaryl (Sevin and other brand names) too is effective. The pyrethroid products generally provide 2-3 weeks protection of plant foliage while carbaryl affords 1-2 weeks protection. For those seeking a botanical alternative, Neem products such as Azatrol or Neem-Away (Gardens Alive), or Pyola (pyrethrins in canola oil) provide about 3-4 days deterrence of Japanese beetle feeding. Insecticidal soap, extracts of garlic, hot pepper, or orange peels, and companion planting, however, are generally ineffective.

With all products, foliage and flowers should be thoroughly treated. The application may need to be repeated to prevent reinfestation during the adult flight period. Follow label directions and avoid spraying under windy conditions or when bees are foraging. Be sure the insecticide is registered for use on the plant or crop you intend to spray. If it is a food crop, note the minimum number of days that must be observed between the date of the last application and the date of harvest.

Because Japanese beetles are attracted to favored host plants from a considerable distance, controlling white grubs in the lawn will not protect landscape plants from adult feeding.

Japanese Beetle Traps

Japanese beetle traps are sold in many garden centers. Commercially available traps attract the beetles with two types of baits. One mimics the scent of virgin female beetles and is highly attractive to males. The other bait is a sweet-smelling food-type lure that attracts both sexes. This combination of ingredients is such a powerful attractant that traps can draw in thousands of beetles in a day.

Unfortunately, research conducted at the University of Kentucky showed that the traps attract many more beetles than are actually caught. Consequently, susceptible plants along the flight path of the beetles and in the vicinity of traps are likely to suffer much more damage than if no traps are used at all.

In most landscape situations, use of Japanese beetle traps probably will do more harm than good. If you experiment with traps, be sure to place them well away from gardens and landscape plants.

Mention or display of a trademark, proprietary product, or firm in text or figures does not constitute an endorsement and does not imply approval to the exclusion of other suitable products or firms.

Issued: 1/06
Revised: 1/06

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!

Photos: Dan Potter, University of Kentucky Entomology. Beetle life cycle diagram: J. Kalisch, University of Nebraska

How to Get Rid of Japanese Beetles

Good horticultural practices, including watering and fertilizing, will reduce the damage caused by these beetles, but oftentimes you simply need to get rid of them. Here are some ideas:

  • Row Covers: Protect your plants from Japanese beetles with row covers during the 6- to 8-week feeding period that begins in mid- to late May in the southern U.S. and in mid- to late June in the North. Row covers will keep the pests out, but they will keep pollinators out, too; be sure to remove them if your crops need to be pollinated.
  • Hand Pick: Unfortunately, the most effective way of getting rid of Japanese beetles is to hand pick them off of plants. It’s time consuming, but it works, especially if you are diligent. When you pick them off, put them in a solution of 1 tablespoon of liquid dishwashing detergent and water, which will cause them to drown.
  • Neem Oil: Neem oil and sprays containing potassium bicarbonate are somewhat effective, especially on roses. The adult beetles ingest a chemical in the neem oil and pass it on in their eggs, and the resulting larvae die before they become adults. Note: Neem can be harmful to fish and other aquatic life, so don’t use it near lakes, rivers, and ponds. It must be reapplied after rain.
  • Use a Dropcloth: Put down a dropcloth and, in the early morning when the beetles are most active, shake them off and dump them into a bucket of soapy water.
  • Insecticides: If you wish to spray or dust with insecticides, speak to your local cooperative extension or garden center about approved insecticides in your area.
    • Or, try this safe homemade solution: Mix 1 teaspoon of liquid dishwashing detergent with 1 cup of vegetable oil and shake well; then add it to 1 quart of water. Add 1 cup of rubbing alcohol and shake vigorously to emulsify. Pour this mixture into a spray bottle and use it at ten-day intervals on pests. Homemade sprays can run more of a risk of damaging plant leaves, so be careful.
    • Apply sprays in the morning, never in full sun or at temperatures above 90ºF. If your plants start to wilt, rinse the leaves immediately with clean water.
  • Traps: Japanese beetle traps can be helpful in controlling large numbers of beetles, but they also might attract beetles from beyond your yard. Eugenol and geraniol, aromatic chemicals extracted from plants, are attractive to adult Japanese beetles as well as to other insects. Unfortunately, the traps do not effectively suppress adults and might even result in a higher localized population. If you want to try them, be sure to place traps far away from target plants so that the beetles do not land on your favored flowers and crops on their way to the traps.
    • Fruit Cocktail Trap: You can buy Japanese beetle traps of all sorts, but most are no more effective than a can of fruit cocktail. Open the can and let it sit in the sun for a week to ferment. Then place it on top of bricks or wood blocks in a light-colored pail, and fill the pail with water to just below the top of the can. Place the pail about 25 feet from the plants you want to protect. The beetles will head for the sweet bait, fall into the water, and drown. If rain dilutes the bait, start over.
  • Geraniums: Japanese beetles are attracted to geraniums. They eat the blossoms, promptly get dizzy from the natural chemicals in the geranium, fall down, and permit you to dispose of them conveniently with a dustpan and brush. Plant geraniums close to more valuable plants which you wish to save from the ravages of Japanese beetles.
  • Japanese Beetles on Roses? Note that insecticides will not fully protect roses, which unfold too fast and are especially attractive to beetles. When beetles are most abundant on roses, nip the buds and spray the bushes to protect the leaves. When the beetles become scarce, let the bushes bloom again. Timeliness and thoroughness of application are very important. Begin treatment as soon as beetles appear, before damage is done.

For rose growers, see our Growing Guide for Roses for more tips on caring for roses!


Photo Credit: Jeff Hahn, University of Minnesota. Sometimes the easiest way to get rid of Japanese beetles is to pick them off the plants before they do too much damage.

How to Prevent Japanese Beetles

Unfortunately, there is no magic potion to get rid of this pest. For general preventive maintenance, experts recommend keeping your landscape healthy. Remove diseased and poorly nourished trees as well as any prematurely ripening or diseased fruits, which can attract Japanese beetles. Try these tips:

  • Choose the Right Plants: Select plants that Japanese beetles will not be attracted to. See our list of the Best and Worst Plants for Japanese Beetles. Dispersing their favorite plants throughout the landscape, rather than grouping them together, can also help.
  • Get Rid of Grubs: In the grub stage of late spring and fall (beetles have two life cycles per season), spray the lawn with 2 tablespoons of liquid dishwashing soap diluted in 1 gallon of water per 1,000 square feet. The grubs will surface and the birds will love you. Spray once each week until no more grubs surface.
  • Milky Spore: You can introduce the fungal disease milky spore into your lawn to control the Japanese beetle larvae population. The grubs ingest the spores as they feed in the soil. The spore count must be up for two to three years for this method to be effective. Fortunately, the spores remain viable in the soil for years. This is an expensive treatment, as all the soil within five-eights of a mile needs to be treated for good control.
  • Beneficial Nematodes: You can also drench sod with parasitic nematodes to control the larvae. The nematodes must be applied when the grubs are small and if the lawn is irrigated before and after application. Preparations containing the Heterorhabditis species seem to be most effective.
  • Plant Strategically: Companion planting can be a useful strategy in preventing pests. Try planting garlic, rue, or tansy near your affected plants to deter Japanese beetles.
  • Parasitic Wasps: You can also attract native species of parasitic wasps (Tiphia vernalis or T. popilliavora) and flies to your garden, as they are predators of the beetles and can be beneficial insects. They will probably attack the larvae, but they are not very effective in reducing the overall beetle population.

NOTE: Many dusts or sprays are highly toxic to honeybees, native bees, and other pollinators. If application of these materials to plants is necessary during the bloom period, do not apply during hours when bees are visiting the flowers (late morning through mid-day). If more than just a few yard and garden plantings are to be treated, you may need to contact nearby beekeepers in advance so that they can protect their colonies.

Geraniums could help control devastating Japanese beetle

Geraniums may hold the key to controlling the devastating Japanese beetle, which feeds on nearly 300 plant species and costs the ornamental plant industry $450 million in damage each year, according to scientists with the Agricultural Research Service (ARS).

The beetle, Popillia japonica Newman, can feast on a wide variety of plants, including ornamentals, soybean, maize, fruits and vegetables. But within 30 minutes of consuming geranium petals, the beetle rolls over on its back, its legs and antennae slowly twitch, and it remains paralyzed for several hours. The beetles typically recover within 24 hours when paralyzed under laboratory conditions, but they often succumb to death under field conditions after predators spot and devour the beetles while they are helpless.

ARS entomologist Chris Ranger at the agency’s Application Technology Research Unit in Wooster, Ohio, is working on developing a way to use geraniums to control the beetles.

Ohio and neighboring Michigan are some of the largest producers of horticultural plants, most of them grown in greenhouses. Other research to benefit the horticultural industry includes that of Susan Stieve, curator of Ohio State University’s Ornamental Plant Germplasm Center in Columbus, Ohio.

Stieve is working with OSU collaborators and horticulturist Jonathan Frantz of the ARS Greenhouse Production Research Group in Toledo, Ohio, to see whether a specialized breed of begonias can tolerate colder temperatures.

The scientists are screening the begonias at two production temperatures: 5 degrees Fahrenheit colder than normal, and 10 degrees F colder than normal. Begonias are found naturally in a wide variety of climates and altitudes—ecological clues that can be used to identify promising germplasm. Being able to grow begonias at cooler temperatures could reduce greenhouse heating bills for ornamental growers in northern climates.

Explore further

‘TRAP’ preserves genetic properties of popular geranium Provided by United States Department of Agriculture-Research, Education, and Economics Citation: Geraniums could help control devastating Japanese beetle (2010, March 8) retrieved 1 February 2020 from https://phys.org/news/2010-03-geraniums-devastating-japanese-beetle.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

How to Kill Japanese Beetles on Geraniums

geranium image by szildy from Fotolia.com

The Japanese beetle (Popillia japonica Newman), brought into the United States in 1916 from Japan, has been extremely destructive to the foliage, roots and fruits of numerous North American plants, lawns, shrubs and trees. The geranium is a favorite of the Japanese beetle. However, once they consume geranium foliage and flowers, most Japanese beetles are rendered paralyzed and many die, according to Michigan State University. The geraniol oil produced by geraniums is toxic to the beetles.

geranium image by photografika from Fotolia.com

Place your geraniums in full sun, which according to Michigan State University increases the toxic effect of geraniol oil in the geranium. Once Japanese beetles feed on the geraniums they tend to drop off the plant to die within eight to 12 hours. Gather the Japanese beetle carcasses up daily and dispose of them.

Pour 4 cups of water into a small pan. Mix 1/2 cup of dish detergent into the water using your hand or a spoon. The water should appear soapy but not bubbly.

Hold the pan of soapy water under the geranium in the early morning, when Japanese beetles tend to be sluggish and less likely to flee. Gently shake the plant’s foliage so that the beetles fall into the pan. The soap will make it impossible for them to climb out of the pan, and they will drown.

Spray the geranium plant with a pyrethrum-based pesticide if the infestation is heavy. Use the pesticide every three or four days to control Japanese beetles. Follow the instructions on the label for application.

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