As an avid gardener, you may be right to think that the Japanese beetle is your sworn enemy. This little beetle is a native of Japan, where it doesn’t cause much horticultural damage, but in the United States, they are an invasive species treating your carefully tended rosebushes, shrubs, and even grassy lawns as an all-you-can-eat buffet. They are easy to spot during the day in your garden, chewing and leaving leaf skeletons as their calling card among your plants. But as the sun sets, they seem to disappear. Where do they go?
If you want to learn more about these enemies of garden foliage and find out how to control these invasive pests in all stages of the critters’ lifecycle and development. Here is what you need to know.
The Japanese beetle is smallish, green-and-copper in color, and actually quite a pretty-looking beetle from the scarab beetle family. It is active during the day but disappears in the evening.
Where do they go? At night, the Japanese beetles burrow underground, and the only clue that they exist in your garden is a small opening visible on the soil’s surface.
In This Article
Is The Japanese Beetle A Serious Threat?
Japanese beetles are voracious eaters. They spend most of their daylight hours eating. And if they are not eating your plants, they will eat your neighbor’s plants. So, the only way to stop the plant carnage is to kill the little beasts.
It is important to prevent the establishment of permanent colonies because the infestation can cause serious damage to plant nurseries, seedbeds, orchards, and field crops. The adults usually attack plants from the top down, munching their way through the foliage and flower heads. At the same time, the growing grubs attack plants from the bottom and can destroy the roots of garden crops like beans and tomatoes as well as other roots like corn plants or strawberries.
They can even bring down massive trees by destroying the leaf canopy until the tree cannot support its living functions and the leaves become brown.
The golf course, park, and cemetery owners consider the Japanese beetles their number one pest. A large population can kill substantial areas of grass and affect the viability of their business. So, it looks like there are no redeeming qualities to this species of beetle.
Can The Japanese Beetle Be A Friend?
As an invasive species, the Japanese beetle is not a friend, and its numbers must be controlled to protect plants. The species is not fussy about what they eat, and there are over 300 types of plants that the critter can devour. The beetles are very good at destroying all vegetation, especially ornamental plants like roses and strawberries.
A visit from a Japanese beetle on a rose bush leaves the plant damaged, with all the leaf matter eaten and only the skeletons of leaf veins left. By the way, it is a unique, telling feature that your plants are under attack specifically by the Japanese beetle’s infestation, as opposed to other beetles or insects.
Even grass does not escape their appetite for vegetation. In their larva stage, the Japanese Beetle lives underground and loves to chew on the roots of grasses and damage the plants to such an extent that they can die. You can see if your lawn harbors Japanese beetle grubs by the randomly spaced patches of yellow, dead grass.
Since the Japanese beetle does not have any natural predators in the U.S., its numbers can multiply exponentially if left unchecked. It is up to us to control the numbers of these insects to prevent a plague.
Their only redeeming quality is that they are harmless to humans because their jaws cannot break human skin, and if collected directly from the plants, the beetles can be eaten by chickens, made into fishing lures, or provide a peaceful zen activity for gardeners who can spend many hours picking adult beetles from their plants and popping them into a container filled with water with or without added soap.
Of course, if you don’t have chickens in your garden, are not interested in fishing, and the feel of the beetle on your skin fills you with dread, you will need to find other ways to kill invaders.
How To Make The Japanese Beetle Leave Your Plants Alone?
Once a Japanese beetle lands in your garden, it will not leave willingly, and it is up to you to either prevent it from landing on your patch in the first place or forcibly remove the ones that do land in your garden.
Probably the best type of defense against the Japanese beetle is to discourage it from moving in. Following practices will discourage the Japanese beetles from using your plants as their buffet.
- Plant pungent-smelling plants like garlic, rue, or tansy around the plants you want to protect. These strong smells can act as a barrier against the Japanese beetle.
- One fun fact about the Japanese beetle is that the smell of its own death repels it. To prevent Japanese beetle invasion in your garden, take some dead beetles and crunch them up. Mix them with water to make a spray, and use it to spray the plants you want to protect. The adult Japanese beetles will avoid landing on those plants where they can smell the dead beetle smell. You may need to spray this mixture regularly to keep the smell in the air.
- Use a trap crop like geraniums or African marigolds. Japanese beetles are partial to eating these particular flowers, but when they do, they become paralyzed by the natural toxins present in those plants. Paralyzed beetles fall to the ground, where birds can find and eat them or pick you can pick them up yourself.
Once you see some adult beetles feeding on your plants during summer, you can be sure there will be a grub infestation underground, ready to emerge next summer. You can interrupt the lifecycle by treating the grub stage by spraying insecticide in mid-to-late summer when newly hatched grubs are small and actively feeding near the surface.
The process should be repeated again in early spring when the over-wintering grubs emerge to transform into adult beetles.
Once the beetles reach their adult form, you can continue destroying them to prevent the establishment of colonies.
- You can catch the beetles by hand. The Japanese beetle is quite slow and easy to pick directly off the plant. A simple pop into a bucket of water will prevent it from flying away. If you want to kill the beetle, add some soap to the water before popping in the beetles. The simple soap effectively kills them without exposing you to harmful chemicals. Some people find catching beetles relaxes them and love to spend hours in the garden just picking Japanese beetles off their plants.
- If you are not partial to touching the beetles with your hands, you can control their numbers by using commercially available insecticide sprays to protect your plants and edible crops in your garden.
- Use commercially available traps. This method is quite controversial because the traps actually attract the beetles to your garden. Even though many of the adults end up dead inside the traps, there will always be a small percentage of individuals who will survive and try to start a colony in your garden.
Eco-Friendly, Natural Alternatives To Chemical Pesticides
If you feel that you don’t want to use chemical pesticides as a way to combat the Japanese beetle infestation, you can try using biological agents like entomopathogenic fungi (mold) to kill the beetles.
The mold is transferred to the beetles through a trap that attracts beetles. The trap has a container where the mold is transferred onto the body of the beetle, attaching to it and killing it through the release of pathogens. If the beetle exits the trap, it can become the spreader of the pathogens, taking it and transferring it to other beetles who come into close contact with the affected individual.
The second natural alternative way to kill the beetles is to apply beneficial nematodes. The heterorhabditis bacteriophora species of nematode can kill grubs that live underground. The nematode is harmless to plants, humans, and other beneficial insects. It finds Japanese beetle grubs, actively seeking them out by detecting carbon dioxide concentration in the soil. Once they locate the grub, the nematodes use natural body openings to enter the insect. Once inside, they release bacteria that overwhelm the grub’s immunity, and the insect dies of septicemia. Destroying the grubs underground prevents the insect from reaching maturity and starting new colonies.
Japanese beetle can wreak havoc in your garden if it becomes established. They are voracious eaters and can destroy decorative plants as well as food crops. Without any natural predators, they can easily multiply out of control. Luckily, the species are relatively easy to dispose of. By ensuring you follow a regular regimen of disposing of the critter at all stages of its lifecycle, you will be able to protect your beloved garden from the Japanese beetle invasion.
Frequently Asked Questions
Additional Sources & Resources
-http://nysipm.cornell.edu/factsheets/?q=show fact sheet&id=147
-https://content.ces.ncsu.edu/-/media/Files/departments /Entomology /publications /Bulletins /EENY%20576%20Japanese%20Beetle%20-%20Popillia%20japonica.pdf?la=en