How to Identify and Eliminate Japanese Beetles in Your Garden

Japanese beetles can be devastating to a garden, but be reassured that in most cases, they only stick around for a short time. If you can kill the scout beetles when they first arrive, you will be much less likely to have more beetles move into the neighbourhood.

Identifying Japanese Beetles

Japanese beetles are small little pests that are only about ½” long. Their wings are metallic brown, to copper color, and attached to a metallic blue-green body. You’ll also notice small white hairs lining the sides of the body. They are related to the June beetle, and European chafer, which are other types of scarab beetles.

Japanese beetles follow a typical insect life cycle where they lay eggs, develop into larvae, and then metamorphose into adult beetles. Adults typically lay their eggs in the soil in June. The eggs hatch into white grubs. The grubs stay in the soil for the remainder of the growing season and through the winter.

The following spring, they emerge and can wreck havoc on your plants. If you notice plants that have all but the veins eaten off their leaves, you probably have a Japanese beetle problem. They usually congregate together, which is why they can do extensive damage so quickly.

These beetles are small pests that carry a big threat. They do not discriminate on what types of plants to feed on, in fact, they are classified as a pest to hundreds of different species. They are one of the most major insect pests in the Eastern and Midwestern US, causing monumental damage to crops each year. Native to Japan, they were first documented in the US in 1919, and have since spread across the country.” (almanac.com)

If you have trees like Ash, Boxwood, Dogwood, Hemlock, or Magnolia, you probably don’t have a big problem with Japanese beetles because they usually don’t like these species. If you have planted fruit trees, birch, or particularly roses, look out. Japanese beetles will likely visit you soon.

Removing the Adults

Getting rid of Japanese beetles can be a long process, but there are several options. The first, and most important, is to be in the lookout for Japanese beetles early on in the season. As soon as you see some, get rid of them. These are probably scout beetles looking for the ideal garden to bring their relatives to.

When scout beetles find a suitable garden, they send off a scent that attracts others. If you kill the scouts right away, you will be more likely to avoid a major infestation. If your plants are already under attack, there is still some hope, though your garden will take a much harder beating.

The most effective, most time consuming, and least pleasant option is to hand pick them. Grab every beetle you see, and drop them into a container of soapy water. Even if you missed the scouts, pick off as many beetles as you can. The more you kill, the less there are to lay eggs that will infest your garden next season. If you don’t want to actually touch the bugs, remove them early in the morning, when they are sleepy and can be shaken off the plants into a container of soapy water.

There is such thing as a pheromone beetle trap. This isn’t a good option. It’s actually more of a scientific tool that’s used for counting how many beetles are around, rather than a pest control device. Because of the pheromones, it will probably attract even more beetles to your yard.

Covering rows of plants with netted hoop houses can reduce the number of adults that can lay eggs on a certain section of soil. The risk of excessive row covering is that you will also be restricting the access for beneficial plants, such as pollinators. This is an effective option for reducing the beetle population for the following year.

While some birds will consume a lot of beetles, they usually don’t like to eat Japanese Beetles, so don’t expect birds to eat the bugs off your plants.

Controlling the Larvae

Since it is nearly impossible to rid your garden of adult Japanese beetles, you need to find a way to target the larvae. There are several options for achieving this.

Use a nematode preparation. A nematode is a small worm, microscopic in fact, that will feed on Japanese beetle grubs before they emerge from the ground. Heterorhabditis bacteriophora is the type of nematode you need. This creature won’t become established in the soil, so it will have to be reapplied regularly. In order to thrive, the soil needs to be about 50-degrees Fahrenheit and reasonably moist. Because of the amount of re-application required, nematodes could be too expensive to use in the long term.

Something called ‘Milky Spore’ has a similar effect. Milky Disease Spore is the common name for Bacillus papillae, which are bacterial spores that will kill grubs when ingested. Good control takes several years, but if you keep treating your lawn areas, the milky spores will build up in the soil and greatly reduce your grub population.

To insure the milky spores get well established, don’t treat your lawn with any chemical pesticides while you are using milky spores. In place of milky spores, you can also use Bacillus thuringiensis japonesis, a natural bacteria more commonly known as Bjt. When applied to the soil, Bjt will destroy a larva’s digestive system.

Gardeners who don’t want to resort to chemical spraying will have to hand pick as much as possible, then live and let live. The life cycle of the Japanese beetle is only about a month, so depending on the type of plants you have, and the time of year, sometimes it’s better to just let the infestation run its course while you do what you can to reduce the larvae population for next year.

Using Chemical Spray

If the natural methods don’t work, you may have to resort to chemical measures. There are only a few chemical products that are properly registered for Japanese beetles. Before using a pesticide, check with a pest control expert, or your local agricultural extension agent. But Gardening Know How recommends one chemical: “Pyrethrin-based insecticide is a safe and effective way to control these pests on vegetables, grapes, raspberries, flowers, roses, trees and shrubs.”

If you find you are having long term beetle problems, dig up a few sections of lawn and count how many grubs are there. If there are more than twelve grubs in a 12” section of sod, you should consider treating your lawn with some sort of grub controlling product. Grubs eat the roots of grass, and reduce its ability to suck up moisture from the soil.

If you notice that your lawn has large dead patches, that can be easily rolled up so you can view the chewed off roots, you probably have a major grub infestation. Irrigated lawn can tolerate a higher grub population than non-irrigated lawn because the irrigation helps make up for the lack of root on the grass stems.

If you are going to spray with pesticides, do so mid-late June when the adult beetles are most active. Usually it is more effective to spray in the morning, or late afternoon when the temperatures are cooler. If you are going to treat your sod with pesticide, this needs to be done between late July and the middle of September when the grubs feeding near the soil surface and will be susceptible to the spray.

Never spray on a windy, or rainy day and be sure you have the proper training to mix and use the product you have chosen. Don’t neglect proper personal protective equipment. Remember that you are working with a type of poison. Don’t spray when bees are nearby. The last thing you want to do is harm pollinators for no reason.

If you really can beat your Japanese beetle population, consider planting a different selection of plants for a few years. Geraniums and Castor Beans are lethal to adult Japanese beetles.

Be diligent at the beginning of the year, by checking plants daily for signs of insect attack. If you see chewed leaves or flowers, check the plant in more detail and see if you can find the insect responsible. If you have a Japanese beetle problem, your neighbours probably do as well. See if you can work together as a neighbourhood to get the problem under control. Even if you manage to remove every beetle from your yard, your plants will still suffer if more bugs keep flying in from your neighbours.

With perseverance and hard work, you can eventually reduce or remove your Japanese beetle problem. Be patient and remember to be proactive by checking plants early in the season, before you have to react to a major infestation.