Are there suddenly holes in the leaves of your favorite plants?
A common culprit is the Japanese beetle. Although the insect is only ½ inch in length, it can do a lot of damage to flowers and vegetables since it usually feeds in groups. It doesn’t help that these beetles aren’t picky eaters – they can and will invade and consume more than 300 species of plants.
It’s important to familiarize yourself with this little insect. Why? Because swarms of Japanese Beetles can quickly decimate your plants. With that in mind, it’s important to be able to identify this insect and what Japanese beetle damage looks like.
What do Japanese Beetles Look Like?
It’s easy to identify the beetle by its distinctive appearance. It has copper-colored back, metallic blue-green head and small white hairs that line the sides of its abdomen. These insects have six legs, two antennae and wings.
It looks exotic and rightly so, as it didn’t originate in North America. Until early in the 20th century, these bugs were only found in Japan. Geographic isolation and certain predators native to the island nation kept the beetle from spreading to the mainland.
That all changed when plants and flowers were imported to the U.S. from Japan in the early 1900s. The bug, probably in larval form, came along too. Hidden in that shipment, they were safely and secretively tucked away in the soil included in the shipment.
Life Cycle of Japanese Beetles
The life cycle of the invasive species spreads out over one year. Each female produces about 40 to 60 eggs, which are laid approximately 3 inches into the soil. By midsummer these eggs begin to hatch.
After hatching, the Japanese beetle grub begins feeding on roots and grasses. That’s the start of your problems with Japanese beetle, because at this stage, the grubs put your lawn at risk. The slug-like grub reaches about 1 inch in length, and by late autumn, it burrows deeper down into the ground before winter strikes. Protected by a thick 4- to 8-inch layer of soil, they remain dormant for the whole winter.
In early spring, the grubs wake from their slumber and begin feeding again. It’s at this point when they reach the pupae phase. After just two weeks, the pupae transform into adult beetles, and they finally emerge from the soil.
Common Habitats for Japanese Beetles
The first of these foreign pests were spotted in 1916 in a plant nursery in New Jersey, and they have been a problem ever since. In fact, the Japanese beetle invasion has been very challenging to control because they can easily adapt to a variety of environments. They inhabit forests and fields, as well as gardens and city parks. Nowhere seems to be off limits for these bugs. More importantly, there seems to be no end to the types of plants they enjoy eating!
You can spot Japanese beetle damage easily. These bugs “skeletonize” foliage, meaning they remove all the plant matter on a leaf except the vein-like support structure. After they’re done, it looks like the skeleton of a leaf.
What Do Japanese Beetles Eat?
The Japanese beetle eats plants throughout its life cycle. It’s just a matter of where they choose to dine depends on their life stage.
As underground larva and pupae, they eat the roots of plants. Once they transition to adults, the beetles emerge from the ground and begin to ravage plant foliage. Some plants are more attractive to the bugs including many fruit trees, such as apple, apricot, cherry, peach and plum, as well as birch trees, asparagus, irises, Norway maples and roses.
How to Prevent Japanese Beetles
It’s important to know how to control Japanese beetles early on, and there are several methods to prevent grubs:
Grow plants Japanese beetles aren’t drawn to: Although these pests aren’t picky eaters, they do have preferences. If they can choose, Japanese beetles have favorite plants to eat.
If you want to plant some Japanese beetle favorites, disperse them: You can keep some of the Japanese beetle’s preferred plants in your garden, just make sure to not group them all together. You don’t want to build a buffet that encourages them feed and multiply. Try companion planting to deter Japanese beetles by mixing their favorites with plants they find distasteful, such as garlic, rue or tansy.
Use a homemade spray to bait the grubs: In late spring and fall, when the beetles are still in grub stage, take advantage of their vulnerabilities. Dilute 2 tablespoons of liquid dishwashing soap with 1 gallon of water. That mixture should cover 1,000 square feet. When you spray this mixture on your lawn, grubs come up to the surface, which leaves them vulnerable to birds and other predators. Continue to spray once a week until grubs no longer surface.
Introduce milky spore: Paenibacillus papillae, also known as milky spore, can be added to the soil and lawn where the larva will unintentionally consume it. Once it’s ingested by the grubs, their body fluids turn milky in color and they die, which in turn releases more of the spores into the soil. The only way this works is if the grubs are feeding, so be sure to add milky spores in the autumn. It’s believed that the larva of Japanese beetles is the only organism susceptible to the milky spore.
How to Get Rid of Japanese Beetles
Once the larva have transformed into adults, you will need to take another approach to get rid of Japanese beetles. If you want to know what kills Japanese beetles, here are seven techniques to try. Consider more than one at a time for maximum control of these pests:
Drape netting over your plants to keep Japanese beetles away. The breathable material allows sunlight in as well as water. This Japanese beetle control provides a simple physical barrier that keeps them from landing on the plant.
This natural way of removing Japanese beetles from your garden is simple and inexpensive, although time-consuming. You simply pick the beetles from the foliage and drop them into a pail of soapy water. This will kill Japanese beetles and guarantee they won’t eat any more of your plants or reproduce to make more problem bugs.
A naturally occurring pesticide, neem oil is yellowy brown in color with a sulfur smell and bitter taste. For hundreds of years, neem has been used to control pests. It still works because the adult beetles ingest the neem oil, which disrupts insect growth, and the same problem is then passed on to their eggs. As a result, larvae die before they are able to mature into adults.
Lay a sheet or large piece of fabric on the ground of your garden. In the morning, pull up the cloth and shake it into a bucket of soapy water. The beetles congregating on the fabric will die in the liquid.
Most Japanese beetle traps have chemical attractants in them that draw beetles to the trap. It’s best to set the trap away from your garden so that the beetles are attracted away from your plants into the trap.
A simple cup or can of fruit cocktail that is allowed to ferment in the sun can also attract Japanese beetles. You place it in a pail of water with a brick in the middle of it about 25 feet away from the plants. The beetles will be lured in by the fruit cocktail, only to drown in the water on their way to it.
Geraniums are enticing to Japanese beetles. However, when they eat the blossoms, they become dizzy and fall off the plant. Then you can simply pick them up and dispose of them. Be warned, this process can be a bit tedious.
Japanese Beetle FAQ
Q. What’s the Japanese beetle’s scientific name?
Q. When are the beetles most active?
They like to be out on warm, sunny days. They prefer plants which are growing in direct sunlight.
Q. Do adult Japanese beetles stay in one garden?
They are very transient and will infest new areas. They can change locations due to a wind shift or the draw of a new food source. Typically, they’ll stick close by plentiful food so they can breed and lay eggs.
Q. How do you know if you’ve got an infestation?
Look for the skeletonizing of outdoors plants – where the Japanese beetles have eaten the green flesh away from the spines/veins of the leaves. If you look more closely, you’ll be able to see adult beetles.
Japanese beetles are very successful pests, as they don’t have any natural predators in North America. However, informed gardeners can reduce and even eliminate the bugs from their property with a variety of these approaches.
John Simcoe is a writer for the Woodstream Corporation, a company that specializes in pest and animal control for the home, farm and garden.