Controlling Japanese Beetles

As devoted gardeners, we start developing a kinship with our plants early on. Especially if you’ve started from seed, most of us become a little emotionally invested in our plants as they develop and mature. So, when suddenly the plants you’ve painstakingly cared for fall under attack, it’s immediately personal.

Insects are some of the most frustrating pests of all. They can be hiding anywhere, there seems to be a limitless supply, and they cause so much damage so quickly. Among the worst offenders is the Japanese beetle, a pest that folks in Simcoe have been trying to eradicate — unsuccessfully — since the 1930s.

Why are Japanese Beetles a Problem?

Japanese beetles managed to hitchhike into Canada by stowing away in travellers’ luggage from East Asia. The first one found in Canada was in the vehicle of a car travelling by ferry to Nova Scotia from Maine in 1939, and since then, the population has erupted. Upon arriving here, the insect had no natural predators and quickly became such an issue for Canadian agriculture, the government soon began a public trapping program to control the spread of the beetles. Clearly, they never did catch them all.

Japanese beetles devour fruit, berries, and plant foliage at an alarming rate. The eat between the veins of plant leaves, leaving them looking like lace doilies. However, they also cause a lot of indirect damage. Their grubs are delicious to burrowing rodents. These rodents will stop at nothing to find and eat them, destroying your lawn and garden as they hunt.

Worst of all, they’re tough. Their shells keep them so well-shielded, any pesticide strong enough to kill them can do much worse damage to friendly organisms—including people!

Identifying Japanese Beetles

An important part of Japanese beetle control is knowing what you’re looking for. Japanese beetles are a species of scarab. The adults are easily identified by their metallic green shells and scarab-like oval shape. The grubs look like C-shaped worms with legs, and can be identified by their bottom sections which are shaped like a V. The adolescents look similar to the adults, but with cream-to-brown coloured bodies and more pronounced wings.

How to Control Japanese Beetles

As horrid as they are, you have to give Japanese beetles credit for being tough to beat. There are a few ways to keep them under control that have proven to be effective.

Japanese Beetle Traps

Japanese beetles do have one weakness: love. The only thing Japanese beetles are attracted to, other than food, are the sex pheromones of a prospective mate. Japanese beetle traps mimic these pheromones, attracting the beetles into an enclosure they cannot escape. These traps can be very effective at persuading the beetles to take a detour away from your garden and keep them there so they’re unable to reproduce. Some traps are also reusable.

An important thing to keep in mind about Japanese beetle traps is that they may end up attracting more beetles than before. To make sure they aren’t doing more harm than good, try to set up the traps farther away from your prized plants, near the edge of your property. Since they only hold around 10-15 bugs at a time, emptying the traps daily is necessary.

Nematodes for Japanese Beetle Control

 If the word ‘nematode’ makes you uneasy, don’t fear. There are some species of nematodes that can be parasitic to humans, but the ones you can purchase at garden centres have a different target: garden pests. These microscopic heroes sneak-attack your garden’s natural enemies — like grubs, gnats, rootworms, and beetles — from the inside. Once the nematode infects a host, like a Japanese beetle, the host normally dies within 24-48 hours. These beneficial nematodes are an effective and organic Japanese beetle control method and are much safer than pesticides. There are many different varieties of nematode available on the market, so make sure you purchase the heterorhabditis bacteriophora nematode, as this one is the best for beetle control.

Soapy Water

There are two ways to use soapy water as a method for killing Japanese beetles. First, you can fill a bucket with soap and water early in the morning, and shake the beetles into the bucket to drown them out. The earlier it is, the better, because like many of us, Japanese beetles are not morning people, and they tend to be extra sluggish. Giving your plants a quick shake should be enough for most of those beetles to fall off. Putting on some gardening gloves, hand-picking the remaining beetles, then tossing them into the bucket should also help the cause. 

Another method that helps prevent beetle damage is filling a spray bottle with a mixture of soapy water, cayenne pepper, and garlic powder. Spritz your plants all over with this unappetizing concoction, and not only will it deter Japanese beetles from munching on your plants, but it should also keep away the rabbits, squirrels and deer.

Plants that Japanese Beetles Can’t Stand

By including plants and flowers that are natural beetle repellents, you can double up on beetle defense without having to resort to much extra effort. These are some of the most effective beetle-repelling plants you can grow in Simcoe:

• Catnip
• Chives/Onions/Leeks
• Chrysanthemums
• White Geraniums
• Marigolds
• Tansy
• Rue
• Larkspur

Worst Case Scenario: Chemical Solutions

While we always recommend proceeding with caution before using harsh chemical solutions in your garden or landscape, sometimes you gotta pull out the bug guns when the beetle damage is out of control. Malathion, which returned to the Ontario market once the beetle problem became severe, can be quite effective in killing those tough-as-nails bugs. However, it’s very important to read the safety directions carefully to prevent injury to yourself or to your garden plants.

While it may be many years, if ever, before we can completely eradicate Japanese beetles, there are a few things we can do to naturally control their spread and the damage they do to the beautiful plants and trees of Simcoe. If you start noticing those lace-doily leaves on your plants, try one of these methods to save your precious plants!