Japanese Beetle Blues

Mating on silver lace vines

Most of us weren't living in New Jersey in 1916, but according to the web that's the state and year when Japanese beetles first showed up in America.  Are they in your yard yet?  If not then enjoy your plants while you can because these guys are on the move and like to eat.  They've been moving westward for many years, well, since 1916.

As you can see from the photos they are large and they are lookers - 1/2 inch long, metallic green with copper wings.  They are serious garden pests -  destructive, unwelcome, dare I say hateful. "Hate" is a strong word, normally reserved for the most extreme situations in life.  Loathsome comes close, but once they take a foothold in your landscape you'll know what they are!

JB on a weed at Washington Park

So, what's a normal summer like with resident Japanese beetles? For me, they simply show up on plants sometime in July.  This year the first sighting was on a container eggplant, there they were (four in all) calmly chewing away on the upper leaves. Their damage is easy to spot - lacy patterns or skeletonized parts on leaf surfaces (they don't eat the leaf veins). If left to their own dining enjoyment they'd do considerable damage to plants. They also eat rose buds, flower petals and leaves of many other trees, ornamentals and annual plants.  Check out the plant lists below.

Prior to seeing adult beetles feeding in the garden they were completing their year-long life cycle from an egg to a chubby C-shaped larvae, pupae, then adult. After feeding during the day adult females will take a late afternoon break and fly to nearby turf or weedy/grassy areas to lay eggs a few inches down near plant roots. Then they happily continue an eating, mating and egg laying cycle during their 6 to 8 week (June to August) adult life on earth. They can lay up to 60 eggs. The egg to grub stage is about four weeks and during that time larvae feed on turf roots and may cause considerable damage to lawns (irregular brown patches). The grubs remain in the soil, eating plant roots and growing in size to 1" in length. They go deeper as temperatures get colder. Adult beetles emerge sometime in June.  Have you had enough Japanese beetle fun yet?  Wait, there's more!

Larvae Photo from UMass Extension

JB Life Cycle from University of Minnesota Extension

Many gardeners aren't very squeamish when it comes to taking care of common pesky insects.  Swat a fly, slap a mosquito, step on an earwig...no problem!  But squish a Japanese beetle while it is calmly destroying your plants? Go ahead!  It's okay to squish them (it's not the smushed parts that attract more beetles to the plant, it's the plant oils released that bring them in droves). Most find it easier to flick them into a jar of soapy water (or gasoline if your enmity is more severe than mine). Or reach for other controls (below).


Japanese beetles like to eat and hang out in groups, the more the merrier to chew, screw and destroy. While feeding, they release pheromones that attract and lure more beetles to join them on their favorite plants. They are sun worshippers and feed the heaviest in temperatures between 85 and 95 degrees

Speaking of eating in groups I remember a comment from the parks manager who runs the public War Memorial Rose Garden in Littleton, CO.  Knowing he had been battling JBs for a few years I asked him what was the most affected rose plant in the memorial garden.  He responded quickly, "hands down, it's 'Garden Party,' a hybrid tea rose."

What controls work on Japanese beetles?  The reality, there's no quick fix like homemade soap spray (we wish).  When they first arrived in our yard three years ago I flicked about six beetles into soapy water the entire summer. That didn't seem like a big deal.  But each year the numbers have increased.  Last year I removed the roses they devoured *('Morden Sunrise'). See comments in chart below about roses and JBs. This year the numbers are incredibly high on the silver lace vines.

Since they are in yards all around the neighborhood there is no way to keep them away entirely.  Even soil treatments to kill the eggs or larvae aren't that effective. They easily travel, up to five miles to plants they favor.  Hand picking for removal and planting plants they don't like are doable.  But if you have a fence or area covered in Virginia creeper, grape or silver lace vines, or linden trees, then your options may need to include using sprays, there are chemical, organic and biological options.

The Palisade area of the West Slope started eradicating Japanese Beetles in 2004 following an area wide plan to chemically treat lawns and ornamental plants.  Without treatment, their grape, wine and peach industry could have been negatively impacted or wiped out.  Read their plan - Eradicating Japanese Beetles

Controls of ADULT Japanese Beetles - 

1., 2., 3. insecticides below have a broad spectrum of activity against many insects including honey bees. NEVER spray any product when bees, butterflies, birds and other beneficial insects are present.  Always read label instructions prior to use.

1. Insecticides that kill on contact or deter - Phyrethroid insecticides (e.g., cyfluthrin, permethrin, bifenthrin, deltamethrin, lambdacyhalothrin, esfenvalerate) are particularly good for this purpose and may provide protection of plants for 2-3 weeks following a single application.

2. Carbaryl (Sevin), control is somewhat shorter than pyrethroids.  Keep in mind that use of Sevin actually increases spider mite numbers.  More - Spider Mites

3. Acetamiprid (Ortho Rose and Flower) is an available option, which has the advantage of moving systemically in the plants.

4. Soil drench containing imidicloprid applied to plant roots 2-4 weeks before adult feeding occurs.  Do not use on food plants or plants visited by pollinators.

5. Hand picking (never squish) in the morning when they are sluggish. Place in soapy jar, empty the jar when full.  Regular removal deters other beetles from congregating.

6. Plant-based, organic insecticides like Neem WITH Azadiractin repel Japanese Beetles for 3-4 days and disrupt their hormonal balance. Repeat applications are required. Beneficial insects do not eat plants, so they are spared, however this product is harmful to fish and other aquatic animals (Read More).  Please note that when using a neem product, it must contain azadiractin to affect JBs. Look for trade names - BioNEEM, Neem Pro, Azatrol.

7. Brand new to the garden market is organic BeetleJUS!™ which is a Bacillus Thuringiensis product.  Bt is a microbiol insecticide and when ingested paralyses the digestive system so the insect pest stops feeding and dies within a few days.

The upside to Btg is they (the manufacturer) say it doesn't hurt the beneficial insects in our gardens - bees, butterflies, lady beetles, people, pets and wildlife.  It can be directly sprayed on adults (BeetleJUS!™) or used on the lawn to target grubs (GrubHALT!™).  This product is not in Colorado garden, only mail order from Gardens Alive or Green Earth Ag and Turf.

8. Other University websites include spinosad for JB control.  Spinosad, organic listed is a toxin made from soil dwelling bacterium. Once ingested, the insect will stop feeding immediately, but it may remain on the plant for a day or two. Spinosad is toxic to bees (when sprayed on them directly), so never spray when they are in the area.

Use of organic products in the garden do not necessarily mean they are without unintended consequences to beneficial insects, people, pets, birds or fish. ALWAYS read the label and ALWAYS spray late in the day when beneficial insects have gone home for the day!!!

Japanese Beetle traps for adults are not recommended, they attract more beetles not only to the trap, but to surrounding plants. Homemade solutions containing garlic, pepper or soaps are not very effective, but you can always give them a try.  Just be careful in mixing your own that you don't burn your plants.

Bacillus thuringiensis (Bt)

Bacillus thuringiensis (Bt)

beetleJUS!™

Controls of Japanese Beetle EGG/LARVAE in turf areas -  Because the beetles are very mobile, controls in your lawn or landscape may have little affect in controlling the number of beetles from year to year.

1. Cultural control option - If possible limit lawn watering during the stage when females lay eggs, late June through July.  They will choose the wettest part of the lawn to lay eggs. Later in the summer, more moisture may actually help the lawn tolerate and recover from damaged roots from grubs.

2. For lawn use to prevent egg laying, or kill eggs or grubs (larvae)
Prevention: *Imidacloprid, trade names - Merit, Zenith, Criterion, also found in Bayer Products
Prevention: *Chlothianidin - Arena
Kill Early Stage Larvae: Chlorantraniliprole - Acelypryn (commercial use only), Scotts Grub-Ex

*Neonicotinoid (neonics) insecticides are often discouraged for lawn use because the chemicals move to plant roots and will affect blooming plants like clover and dandelions, which are often visited by beneficial pollinators. Chlorantraniliprole, a newer product is a lower hazard to pollinators.

Biological Controls
1. Nematodes (small round worms that kill some insects like grubs) in the genus Heterorhabditis (e.g., Heterorhabditis bacteriophora, H. megadis). Read more - Insect Parasitic Nematodes 
Use as a soil drench during cool weather, must be watered in and applied when beetle larvae are present.

2. Milky Spore (Bacillus popilliae), a bacterium that produces ‘milky disease’ in Japanese beetle grubs. (sold under the trade name St. Gabriels’ Organics Milky Spore Powder.)

3. Natural Predators (not widely available or offered in the Denver Metro area that I can find).
    Tachinid Fly - Istocheta aldrichi  Read More
    Parasitic Wasps - Tiphia species Read More
    Microsporidium - Ovavesicula popilliae Read More


Plant Lists compiled from the United States Department of Agriculture USDA Japanese Beetle Home Owner Hand Book and other University websites.  This list is in no way complete (I hope it's fairly accurate, but sometimes I see them on a plant in my yard that I didn't think they liked).  My research says they favor over 300 plants. 

Trees/Shrubs JB Favor	Trees/Shrubs JB Do Not Favor	Perennials JB Favor	Perennials JB Do Not Favor
American and English Elm	Arborvitae	Grape	Hellebore
Birch	Boxelder	Hollyhock	Iris
Black Walnut	Boxwood	*Rose (not ALL roses), comments below	Liatris
Hawthorn	Dogwood	Raspberry	Lily
Horse Chestnut	Euonymus (burning bush)	Virginia Creeper	Columbine
Norway Maple	Forsythia	Silver Lace Vines	Lily-of-the-Valley
Larch	Holly	Hops	Coreopsis
Linden	Juniper	Coneflower	Larkspur
London Planetree	Lilac	Hibiscus	California Poppy
Malus spp. (crabapple, apple, etc.)	Magnolia	Common Mallow	Foxglove
Mountain Ash	Mulberry	Evening Primrose	Coral Bells
Pin Oak	Northern Red Oak	Clematis	Hosta
Pussywillow	Pine	Peony	Impatiens
Prunus (flowering cherry, etc.)	Red and Silver Maples	Joe Pye Weed	Veronica
Beech	Redbud	St. John’s Wort	Forget-me-not
Rose of Sharon	Spruce	Gaura	Pachysandra
	Sweet Gum		Poppy
	Tulip tree		Moss Rose
	Yew		Sedum
	Chokecherry		Yarrow
	Elderberry		Milkweed and Butterfly Weed
	Mockorange		Aster
	Smokebush		Baptisia
	Snowberry		Mums
	Sumac		Dianthus
	Spirea		Bleeding Heart
			Gaillardia
			Geum
			Baby’s Breath
			English Ivy
			Beebalm
			Obedient Plant
			Spiderwort

Annuals/Vegetables/Herbs JB Favor	Annuals/Vegetables/Herbs JB Do Not Favor
Cannas	Begonias
Gladiolus	Caladiums
Sunflower	Dusty Miller
Morning Glory	Ageratum
Cardinal Flower	Lantana
Zinnia	Nasturtium
Anemone	Violet/Pansy
Asparagus	White Geranium
Rhubarb	Snap Dragons
Green Beans
Soybeans	Ornamental Kale
Sweet Corn	Nicotiana
Dahlia	Ornamental Pepper
Strawberries	Petunia
Sweet Potato Vine	Portulaca
Basil	Verbena
Eggplant	Tomatoes
	Garlic
	Rue
	Tansy
	Catnip
	Chives
	Leeks
	Onions
	Tomatillos

 *Roses - some roses seem less favorable to JB, at least in my garden, the lower growing shrub roses have and are not being attacked, they include: 'Gourmet Popcorn,' Flower Carpet Yellow 'Noalesa,' and Flower Carpet Red 'Noare.'  My Kordes 'Brillant' shrub roses are also not being attacked.

For more information read:

Colorado State University Fact Sheet on Japanese Beetles.

University of Minnesota Japanese Beetle Management in Minnesota