How to Identify and Control Japanese Beetles
Are there suddenly holes in the leaves of your favorite plants? A common culprit is the Japanese beetle. Kevin Espiritu explains how to identify and control these invasive bugs.
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Are there suddenly holes in the leaves of your favorite plants? A common culprit is the Japanese beetle. Although the insect is only half an inch in length, it can do a lot of damage to flowers and vegetables.
These beetles aren’t picky eaters. They can and will invade and consume hundreds of species of plants. With that in mind, it’s important to be able to identify this insect and tackle problems as soon as they appear.
If you spot any of these bugs, don’t panic. There are several ways to control and get rid of Japanese beetles, along with a few preventative measures to stop them from coming back in the future.
Identifying Japanese Beetles
The first step in controlling or preventing Japanese beetles is identifying them. Visual clues and understanding their life cycle and habitat will help you spot and treat a small problem before it becomes a big one.
What do Japanese Beetles Look Like?
Japanese beetles have a distinctive appearance that makes them easy to identify. They have copper-colored backs, metallic blue-green heads, and small white hairs that line the sides of their abdomen. These insects have six legs, two antennae, and wings.
They look exotic and rightly so, as they didn’t originate in North America. Until the early 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 came along too.
Life Cycle of Japanese Beetles
The life cycle of this invasive species lasts one year. Each female produces about 40 to 60 eggs laid in 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, putting your plants at risk.
The slug-like grub reaches about an inch in length. By fall, it burrows deeper into the ground before winter strikes. Protected by a thick four to eight-inch layer of soil, they remain dormant for the season.
In early spring, the grubs wake and begin feeding again. Here, they reach the pupae phase. After just two weeks, the pupae transform into adult beetles and emerge from the soil.
Common Habitats
The first of these foreign pests was 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 challenging to control because they can easily adapt to a variety of environments.
Japanese beetles inhabit forests and fields as well as gardens and city parks. Nowhere seems to be off-limits for these bugs. To make matters worse, there also 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. Where they choose to dine depends on their life stage.
As underground larvae and pupae, they eat the roots of plants. Once they transition to adults, the beetles emerge from the ground and eat plant foliage.
Some plants are more attractive to the bugs than others. This includes many fruit trees (specifically apple, apricot, cherry, peach, and plum), birch trees, asparagus, irises, Norway maples, and roses.
How to Prevent Japanese Beetles
It’s best to catch a Japanese beetle infestation before the bugs become adults. Stop the life cycle early by following these tips to control Japanese beetle grubs.
Choose Plants Wisely
Although these pests aren’t picky eaters, they do have preferences. If they can choose, Japanese beetles have favorite plants to eat. Avoid planting those where you can to limit your risk.
Disperse Plants
If you do plant any susceptible plants, disperse them around your garden. Grouping them will encourage the beetles to feed and multiply. Try companion planting to deter Japanese beetles by mixing their favorites with plants they find distasteful, such as garlic or tansy. Tachinid flies are their main predators, and they love asters, yarrow, and fennel too.
Homemade Bait
In late spring and fall when the beetles are still in the grub stage, take advantage of their vulnerabilities with a homemade bait.
Spray a beneficial nematode solution on your yard in these temperate seasons. The best treatments involve two applications that are a week apart. You should do this only when soil temperatures are at least 50°F (10°C) and no more than 75°F (24°C) as nematodes can’t survive outside this range.
Milky Spore
Add Paenibacillus papillae, also known as milky spore, to the soil and lawn where the larvae are. Once it’s ingested by the grubs, their body fluids turn milky in color and they die, which releases more of the spores into the soil. This only works if the grubs are feeding, so be sure to add milky spores in the fall.
How to Get Rid of Japanese Beetles
Once the larvae have transformed into adults, you will need to take another approach to get rid of Japanese beetles. Try several of these control methods simultaneously to protect your plants.
Row Covers
Drape netting over your plants to keep Japanese beetles away. The breathable material allows sunlight and water in but creates a physical barrier that keeps beetles from landing on the plant.
Hand Pick
This natural way of removing Japanese beetles is inexpensive but time-consuming. Simply pick the beetles from the foliage and drop them into a pail of soapy water. This will kill Japanese beetles and ensure they won’t eat any more of your plants or reproduce.
Neem Oil
For hundreds of years, neem oil has been used to control pests. 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 can mature into adults.
Drop Cloth
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.
Traps
Most Japanese beetle traps have chemical attractants to draw beetles to the trap. It’s best to set the trap away from your garden so the beetles are attracted away from your plants. However, recent research has shown that traps are one of the less efficient ways to treat Japanese beetles.
Fruit Cocktail
A simple cup or can of fruit cocktail allowed to ferment in the sun can also attract Japanese beetles. Place it in a pail of water with a brick in the middle 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
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. Geranium works as a trap crop this way.
Final Thoughts
Japanese beetles are successful pests, as they don’t have any natural predators in North America. However, you can reduce and even eliminate the bugs from your property with these approaches.
FAQs
What’s the Japanese beetle’s scientific name?
Popillia japonica.
When are the beetles most active?
They like to be out on warm, sunny days. They prefer plants growing in direct sunlight.
Do adult Japanese beetles stay in one garden?
Japanese beetles can change locations due to a wind shift or the draw of a new food source. Typically, they’ll stick close by plentiful food to breed and lay eggs.
How do you know if you’ve got an infestation?
Look for the skeletonizing of outdoor 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.
