Garden Dilemmas, Delights & Discoveries, Ask Mary Stone, New Jersey Garden blog

Japanese Beetle Time

a cluster of Japanese Beetles looking lifeless

Hello fellow readers, Caught in the act! I found the culprit of Carolyn’s holy rose dilemma we spoke about last week. As I arrived with Pyrethrin in hand, there they were, the shiny green and rust-colored beetles chomping away. Yes, indeed, it’s Japanese beetle time.

Their arrival brings a memory of how Mom hired her five-pack to collect the suckers— five cents a Jiffy jar full. How fun! It was her strategy of killing them that was a bit grim. She’d boil up a pot of water and toss them in. None of us had the courage. Nor have I ever tossed a live lobster into boiling water. Poor things.

Why Japanese Beetle control requires a Two-Punch Strategy 
a green and rust colored Japanese Beetle on a green leaf

Japanese Beetle / Popillia japonica

Japanese beetles (Popillia japonica) are a nuisance even before they become good-looking iridescent beetles. Their crescent-shaped grayish-white larvae, called grubs, live in the soil and feed on the roots of grasses and plants. If there’s a dead area of grass that you can easily lift, you will probably find Japanese beetle grubs as the culprit. On top of which, critters love grubs and rip up the turf to feed on them.

They were first found in New Jersey in 1916 and now are in every state in the eastern U.S. except Florida. And the invasive critters continue to move west.

Adult beetles emerge in late June and feed and mate into September, then lay their eggs back in the soil. And so, controlling them requires a two-part strategy; one for the grubs and one for the beetles.

Punch-One: Pyrethrin 

A few hours after spraying Carolyn’s roses with Bonine Pyrethrin Garden Spray, I sent an email assuring redemption is underway that went like this:

It was fascinating to see how Pyrethrin, derived from chrysanthemum flowers, kills the suckers almost on contact (photo evidence attached). I’ve read about the instant impact on insects’ nervous systems but never witnessed it in action. I felt a tad bad for the beetles. And a bit triumphant too. What a holy mess they’re making of your roses!

Roses are one of their favorite feasts. Plus, about 300 other plants such as fruit trees, berry, and vegetable plants. They’ll do a lot of damage in their feeding frenzy, which lasts four to six weeks. Some folks cover their prized roses with cheesecloth or fine netting during Japanese beetle time.

a cluster of Japanese Beetles looking lifeless

Pyrethrin Working on Contact

I then wrote—Pyrethrin degrades in a day or two, so during work breaks, feel free to spot-spray the beetles for revenge. And stay clear of the tender new foliage as best you can. Hopefully, their friends will see the dead bodies and stay clear— do I sound a tad morbid?

On edible plants, you can use Pyrethrin up to the day before harvest. No more than once a day, though, in the same area of a plant.

Carolyn replied—Well, I must admit, I am not sorry about the beetles as they had no invitation to invade our garden!

Why Japanese Beetle Bag traps don’t work

Good point, Carolyn. By the way, the popular Japanese beetle traps backfire. Sure, many suckers will fall in the bag, but studies have shown the pheromone lures attract many more to your garden than you trap. So rather than inviting your neighbors’ beetles, it’s best to consider a one-two punch.

Punch-two: Milky Spore
a yellow ranch house with a Japanese Beetle Bag in the front yeard

Beetle Bags say, “Welcome, Japanese Beetles!”

Punch two is biological control using milky disease spores called Milky Spore. It’s a safe, all-natural bacteria that is lethal to grubs but harmless to humans, pets, and beneficial insects. Dispense about a teaspoon every 4 feet. Grubs ingest the spore, die then spread the bacteria into the soil. The bacteria will live in the ground for 10-15 years.

True, there are chemical pesticides if you are inclined to use them in July or August when young grubs are feeding, but please don’t tell me about it. I’d prefer you gather Japanese beetles as good old mom hired us to do. And if you’d rather avoid boiling up hot water, tossing them into a bucket of soapy water works too.

Recently I heard if you puree their bodies in a blender and add water to create a spray for plants they chomp, it will infect more grubs with the milky spore disease. Just don’t invite me for a margarita after.

Garden Dilemmas? (and your favorite Podcast App.)

a cluster of shiny green and rust colored Japanese Beetles feeing on a plantLink to last week’s column Rose Remedies. 

More information on why Japanese Beetle Bags backfire 

Link to St. Gabriel Organics Milky Spore Powder




Mary Stone, owner of Stone Associates Landscape Design & Consulting. As a Landscape Designer, I am grateful for the joy of helping others beautify their surroundings which often leads to sharing encouragement and life experiences. These relationships inspired my weekly column published in THE PRESS, 'Garden Dilemmas? Ask Mary', began in 2012. I dream of growing the evolving community of readers into an interactive forum to share encouragement and support in Garden and Personal Recoveries - seeking nature’s inspirations, stimulating growth, weeding undesirables, embracing the unexpected. Thank you for visiting! Mary

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