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

A Jiffy Jar of Japanese Beetles

a yellow ranch house with a Japanese Beetle Bag in the front yeard

Hello fellow readers, I saw the first of the season, as did Tom of Mt. Bethel, who asked if he should hang the Japanese beetle traps you find at the hardware store. The subject opens up a can of worms, or should I say grubs? Studies have shown that these pheromone lures attract many more beetles than they trap. When you hang a Japanese beetle trap in your yard, you’re inviting the neighborhood of Japanese beetles to your garden. You’ll trap a bunch, but the rest will enjoy the call to dinner.


Japanese beetles Popillia japonica

Japanese beetles Popillia japonica are a nuisance even before they become good-looking beetles sporting a green and gold iridescent shell. 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 this, critters love beetle grubs and rip up the turf to feed on them.

Adult beetles begin to emerge in late June and feed and mate into September, then lay their eggs back in the soil. Controlling Japanese beetles requires a two-part strategy; one for the grubs and one for the beetles.

Biological control using milky disease spores called Milky Spore is a safe, all-natural bacteria 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 soil for 10-15 years, providing a long-term solution and can be applied anytime the ground is not frozen. Yes, if you are inclined, chemical pesticides can be used in July or August when young grubs are feeding, but please don’t tell me about it.

I’d rather you gather Japanese beetles as good old mom hired us to do at five cents per Jiffy jar full. You can easily shake beetles from branches into a container. What to do after the catch depends on how squeamish your stomach is. Mom tossed them in a pan of hot water, but a bucket of soapy water works too. Recently I heard if your puree their bodies in a blender and add water to create a spray for plants they chomp, it will infect more grubs with the disease. Just don’t invite me for a margarita after. Garden dilemmas?

You’ll enjoy Episode 65 of the Garden Dilemmas Podcast featuring these unwelcome garden guests:

Check out an updated storySafely Controlling Japanese Beetles. 

Column updated 7/20/22 

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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