Japanese Beetles

Japanese beetles first arrived in Northeast Kansas 4 years ago, and now have a strong foothold to the western wilds. Every year their numbers seem to increase, but then, so do the predators that eat them. Since their arrival, I have seen an exponential increase in tachinid flies and wheel bugs.

Adult Japanese beetle on elm leaf
An adult Japanese beetle feeding on an elm leaf

History of Japanese Beetles

The first beetles were found in a nursery near Riverton, NJ, in 1916. They were thought to have been brought from Japan in a shipment of bulbs, before the start of inspection, which began in 1912.

They have moved relatively slow across the United States but can be found in almost every state now. They are good fliers and quick to drop off plants when disturbed in their feeding.

What do Japanese Beetles Eat?

Japanese beetles are voracious eaters, defoliating plants and creating a “lacy” look to many leaves. They also eat flowers and fruit. The beetles are attracted to sweet-smelling plants such as roses, lindens, peaches, cherries, apples, evening primrose, apricots, grapes, and elms.

However, they also eat many other things, making them a definite pest in the garden. I have also seen them on willows, oakleaf hydrangeas, blueberries, chokeberries, thistles, milkweeds, and others.

In the vegetable garden they may go for beans, corn, tomatoes, and peppers.

Japanese beetles on roses
Japanese beetle destruction on roses

What is the first line of defense against Japanese Beetles?

Plant some tall or common evening primroses, Oenothera biennis. I have found that the beetles are attracted to this native biennial first in my landscape. I use it as a trap crop, to lure them in and destroy as many as I can before turning to chemical applications. Once they land on these plants, I go out in the evening (around 8 P.M.), and knock them off into a pail of soapy water.

A bucket of soapy water with Japanese beetles
My bucket of soapy water

What chemicals are best used for the adult beetles?

There are now many chemicals being labeled for killing Japanese beetles. However, some are much better than others. Over the years I have noticed that many homeowners seem to have a fondness for Sevin or Sevin dust, which is the chemical Carbaryl. This chemical has a short residual, and the dust is very dangerous to bees and beneficials.

  • Bifenthrin – this chemical has one of the best residuals for any insecticide on the market, lasting upwards of 2 weeks once dried. It is highly effective against the beetles, though it takes 1-3 days for chemical to actually kill the beetle. Trade names include Hero, Bug Blaster, and Talstar.
  • Lambda-cyhalothrin – relatively unheard of by homeowners, it is fast becoming a favorite of gardeners as the go-to chemical for killing beetles. The residual of this chemical is 10 to 12 days. The best known trade name is Cyonara.
  • Acetamiprid – Another good chemical with up to 2 weeks of residual action. Trade name is Assail.

Always read and follow all chemical labels before spraying on plants. Remember, these chemical are toxic to bees and other wildlife, be sure to spray when bees are least active, such as in early morning or late evening.

What is the life cycle of the Japanese Beetle?

The beetles overwinter in the soil as larvae. They begin to feed in the soil on grass and turf roots in April and continue through May. in late May or June, they form a pupa in the soil and begin the process of changing into an adult beetle.

The adults emerge in June or July and feed for about 3-5 weeks on plants, fruits, and flowers. The adults are constantly mating while feeding, then flying down to lay eggs in turf. And what is in the United States? Millions of acres of turf in lawns, golf courses, and sports fields. The eggs hatch and the larvae feed on the roots of the grass until September. Then they burrow deeper into the soil to overwinter.

Is Grub Treatment a good option?

It can be. If you have a nice lawn that you want to maintain at a high level and keep unwanted moles from it, as well as grub damage, then a treatment of insecticide is necessary. However, this will not prevent Japanese beetles from coming into your garden, it merely to keep your lawn clean.

The best recommendation for lawn treatment it the granular insecticide Merit, which contains Imidacloprid. This is best if applied in August to catch the larvae as it feed on turf roots.

Is Milky Spore a viable option for the lawn?

If you are an organic gardener or want a chemical-free lawn, this is the only option available. It takes about 1 year to get established in the lawn, but can last for up to 10 years. However, the grubs have to actually ingest it for it to work, and it may not always be in the vicinity of them. Milky spore should be applied in August and September.

Do Japanese Beetle Traps work?

Yes if you want more beetles than usual coming into your yard. The traps work with a scent for the male beetles and a pheremone for the female beetles.

Beetles are attracted by the scents from as far away as 800 feet, and may reach farther when the wind is blowing. If you live on a small lot, surrounded by neighbors, I would not recommend the traps, as they will attract not only your beetles, but all your neighbor’s beetles as well, an they eat on their way to the trap.

If you have the space and time, separate the the pheremone and male lure into separate traps on opposite sides of your property. This will disrupt the mating cycle and kill more beetles.

Fun Fact about Japanese Beetles

You can eat them! Yes, you heard me correctly, you can eat them. In Japan, and other places where the beetles are prevalent, they are captured, killed, then cooked and eaten. Most Americans shy away from eating bugs and insects, because we have disregarded them as a food source in our culture.

However, beetles are high in protein and nutrients, and can be good in stir-fries, as roasted snacks, or mixed into other dishes.

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