A healthy garden is all about equilibrium – even garden pests like slugs and snails have an important role to play! However, when something foreign is introduced to a new ecosystem or garden, the effects can be damaging. Enter: Japanese beetles! 

Today, we’ll teach you everything you need to know about this hungry garden destroyer. We’ll help you understand its lifecycle, what you can do to manage it, and how to stop this invasive species from destroying your garden. 

collage of Japanese beetle photos

My Experience with Japanese Beetles

Before we get into the details, I’ll let you know my experience in dealing with a Japanese beetle infestation. They first arrived in our garden a few years ago, and mostly targeted our blackberries and the zinnias in my cut flower garden. Their numbers increased rapidly from year to year, and I’m slightly terrified to see how many show up this summer.

They’re nearly impossible to get ride of, but my advice is this: be persistent! You’d be surprised at just how much a difference you can make by getting out into the garden and picking them off your plants. I took this approach and would sometimes knock them into cups of water without soap so we could feed them to our chickens. If I took a few days off, their numbers in the garden would increase significantly in the garden. All that’s to say – you can make a difference with your own two hands, I promise!

What Are Japanese Beetles?

Japanese beetles (Popillia japonica) are a species of invasive insect notorious for their destructive feeding habits and widespread damage to a variety of plants. Belonging to the scarab beetle family Scarabaeidae, these metallic green and bronze-colored pests have become a significant concern for gardeners, farmers, and horticulturists across North America.

How to Identify Japanese Beetles

Before you learn how to deal with them, it’s important to confirm that you’re actually dealing with Japanese beetles. They’re around half an inch in length and have distinct metallic green thoraxes and copper-colored backs or wing covers. You may notice them around late June or early July depending on your location. Once you know what Japanese beetles look like, they’re pretty easy to identify.

Japanese beetle close up
Photo source: UMN

Some other identifying factors:

  • Clumsiness: if you walk right up to a beetle on a plant and shake the plant, they’ll likely fall instead of flying away.
  • Clusters: you’ll often see Japanese beetles in clusters or on top of one another. Where there’s one, there’s usually more- especially later in July or early August when their population usually peaks.

How this Pest Make It to North America?

Originally native to Japan, the Japanese beetle likely arrived in North America unintentionally through imported plant material in the early 20th century. They were first detected in the United States in 1916, in a nursery near Riverton, New Jersey. Since then, they have spread rapidly across the continent, facilitated by factors such as favorable climatic conditions, abundant food sources, and lack of natural predators.

The Life Cycle of Japanese Beetles

You can’t learn how to control these pests without first understanding the Japanese beetle life cycle. They undergo complete metamorphosis, with four distinct stages: 

  • Egg: Females lay their eggs in the soil during mid-summer, typically in grassy areas. These eggs hatch within two weeks, giving rise to the next generation of larvae.
  • Larva: The larval stage, or Japanese beetle grub, is the most damaging phase of the Japanese beetle’s life cycle. Grubs feed on your grass roots and various ornamental plants, causing extensive damage if uncontrolled.
  • Pupa: After completing their feeding phase, grubs transform into pupae, a non-feeding stage during which they undergo metamorphosis into adult beetles. Pupae remain dormant in the soil throughout winter and early spring.
  • Adult: Emerging from the soil in late spring to early summer, adult Japanese beetle adults feed on the foliage and flowers of a wide variety of plants, including both ornamentals and edible crops. Then, head right back into your lawn to lay eggs for next year.

What Can Japanese Beetles Do to Your Garden?

If you’ve dealt with Japanese beetles before, you’ll know the damage they can cause. If you haven’t, here’s what you can expect from these pests if they’re left to their own devices. 

Types of Plants Commonly Affected

Japanese beetles will eat just about anything, but they’re particularly fond of plants with succulent foliage and fragrant flowers. Some of the most commonly affected plants include roses, linden trees, fruit trees (such as cherry, apple, and plum), grapevines, raspberries, zinnias, and various ornamental shrubs and perennials.

Japanese beetle on a leaf

What Damage Do Japanese Beetles Cause?

The feeding habits of Japanese beetles result in distinct patterns of damage that are easily recognizable. Adult beetles feed on the foliage of plants, consuming the tissue between the veins and leaving behind skeletonized leaves with a lace-like appearance. 

They also target flowers, devouring petals and reproductive structures, which can impact the plant’s ability to produce seeds and fruits. Japanese beetle larvae (grubs) also feed on the roots of grasses and ornamental plants, causing wilting, yellowing, and eventual dieback.

What’s the Long-Term Impact

If left unchecked, Japanese beetles can pretty much destroy your garden. They’ll strip the leaves off your plants, which weakens them and makes them more vulnerable to secondary pests, diseases, and environmental stress. 

skeletonized leaves from Japanese beetle damage
Photo source: UMN

Japanese beetle larvae can cause extensive root damage, leading to stunted growth, decline, and even death of affected plants. You can use whole crops because of these pests, which is why it’s so important to take Japanese beetle control measures. 

Preventing Japanese Beetle Infestations 

If you’re not currently dealing with Japanese beetles, it’s a good idea to keep it that way! Here are some of the strategies you can use to reduce the chances that these beetles will find a home in your garden. 

How Proper Garden Maintenance Keeps Japanese Beetles Away

Maintaining a healthy garden environment is crucial for deterring many pests, including Japanese beetle infestations. Proper watering, fertilization, and pruning help keep your plants healthy and resilient against pests. 

Removing weeds and debris from the garden eliminates potential breeding and hiding spots for Japanese beetles and their larvae. Also, rotating susceptible plants and diversifying the landscape with less preferred species can disrupt the beetle’s feeding patterns and reduce their attraction to specific areas of your garden.

Do Japanese Beetles Have Natural Predators?

I’ve hear conflicting information on this one. Some say Japanese beetles have no natural predators in North America because they are not native (like in this article for example). However, many sources will say that some birds, toads, and small mammals may consume adult beetles if given the chance (for some examples, see this post, or this one). If any of you reading this happen to have an entomologist friend, let’s ask them to get to the bottom of this!

My understanding after digging into it is that they don’t have any predators out there specifically targeting them. However, native predators of beetles and their larvae may eat them if they happen to come across them while targeting other species.

For example, I’ve been told that birds can make a big difference in controlling beetle numbers by eating larvae in your lawn. And in the same post that notes Japanese beetles have no natural predators, the author suggests beneficial nematodes as a potential solution to targeting Japanese beetles in the larval stage as well.

Either way, these predators are generally not effective at controlling large-scale infestations due to how quickly Japanese beetles can breed and replenish their populations – you can’t really rely on predators in North America to control invasive populations of pests like these beetles. For that reason, a multi-faceted approach is best.

Other Preventative Tips: How to Keep Japanese Beetles off Plants

Luckily, there are a few other things you can do to help keep Japanese beetles off your plants.

  • Physical barriers like floating row covers or fine mesh netting to protect your plants from adult beetles while still allowing air, light, and water to reach the vegetation.
  • Repellents or deterrents, such as neem oil, garlic spray, or kaolin clay, can be applied to foliage to discourage feeding by making plants less palatable to beetles. 
  • Catch them early! I can’t stress this one enough- you can save your plants from a lot of damage by getting ahead of an infestation. Reducing their numbers as soon as you spot these pesky bugs in your garden can prevent them not only from devouring your plants, but also from laying eggs for next year’s infestation.

How to Get Rid of Japanese Beetles in Your Garden 

So, you’ve found Japanese beetles in your garden and they’re starting to wreak havoc. Now what? It might take you some time to get on top of them, but there are a few different ways to wrangle control of your plants and fight back against Japanese beetles! 

First Steps to Take after Identification 

If you don’t start dealing with Japanese beetles right away, they’ll quickly destroy your entire garden – trust me! As soon as you identify the beetles, start by knocking beetles off your plants into a cup of soapy water. It seems simple, but I swear it actually makes a big difference. They’re terrible flyers, too, so it’s surprisingly easy to catch them off guard and bump them into your cup or bucket of soapy water. 

Japanese beetles in soapy water
Photo source: Julie Martens Forney / HGTV

Chemical Controls

Chemical insecticides are a common and effective method for controlling Japanese beetle populations, especially if your infestation is so bad that nothing else is really working. This article by UMN has some great advice on employing this method. Synthetic insecticides containing carbaryl, imidacloprid, or pyrethroids are often effective, just make sure you follow label instructions carefully and only apply insecticides at times or areas of low bee activity. 

Organic and Home Remedies for Japanese Beetle Control 

If chemicals aren’t really your thing, you can try making a DIY Japanese beetle spray (or buying an organic one). Try an insecticidal soap (you can find these in garden or hardware stores, or make your own with dishwashing detergent and vegetable oil. 

You can also try applying diatomaceous earth or neem oil to foliage to deter beetles and interfere with their reproductive cycle. Planting companion plants with natural repellent properties, such as garlic, chives, or alliums, may also help repel Japanese beetles from your garden.

Another companion planting technique, utilizing a trap crop may help bring the beetles away from your favorite plants. Julie Martens Forney suggests marigolds in this post over at HGTV.

japanses beetles eating a marigold
Photo source: Julie Martens Forney / HGTV

Japanese Beetle Traps and How to Use Them

Japanese beetle traps (which use pheromones to attract and trap the beetles) work for some gardeners, but others find that they just seem to bring more beetles to their gardens. If you are going to try them, make sure the pheromone traps are placed at least 30 feet away from your plants, and position them upwind so that you don’t unintentionally lure more beetles into your garden.

Got Any Tips for Japanese Beetle Control? Let Us Know! 

Hopefully, we’ve given you some tips for identifying, preventing, and treating Japanese beetles in your garden. It’s important to stay on top of these pests – despite their small size, they can really do some damage! 

If you’ve dealt with Japanese beetles (either successfully or unsuccessfully) in your garden, we’d love to hear from you! Leave a comment to share your story, and of course any tips you have for saving plants from these hungry pests. 

Looking for tips on keeping other, furrier pests out of your plants? You’ll want to check out our tips for keeping squirrels out of potted plants and bulbs and our guide to keeping deer out of the garden as well!

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