by / Monday, 21 May 2018 / Published in Blog

Nematodes and Japanese Beetles

By Erin Robbins


“Together, even the smallest can achieve the greatest goal.” – A Bug’s Life

For many gardeners, their garden is so much more than just a hobby. We take the time to nurture our plants and enjoy them for their ability to bring some beauty, tranquility, or even fresh food to our homes. It can be heartbreaking to watch all of our hard work disappear.

Under Attack: Pests in the Garden

Weather, animals, grubs, and insect pests are all predators that will target our beloved gardens this year and we must do our best to stop them to keep our garden healthy. Nature, however, is tough to fight sometimes, especially with the chemical bans in our area.

There are few pesticide options that are still effective with a growing list of pests that are resistant to them. One of these seemingly invincible pests is the Japaneses Beetle, and it’s been a growing and devastating problem in Chatham-Kent for the past 4 years.

Japanese Beetle

The Japanese beetle is not native to North America, as implied by its name. They were stowaways that made their way to our continent from Japan and have infested gardens everywhere. They have few natural predators here and a tough outer shell that makes them hard to get rid of. They’re attracted by the sweet fragrance of our beautiful gardens – especially to broadleaf plants like hydrangeas, raspberry, roses, or maples – and work quickly to cause massive damage to our plants.

They are difficult to handle, but identifying these pests in your garden is very simple. The beetles themselves are easy to identify by their bright metallic green heads and copper bodies that appear in hordes. If you can’t spot the insects themselves, their damage is a dead give away. These beetles have an appetite for leaves and petals, but won’t devour the whole thing, leaving behind the veins of your plants like eerie skeletons, causing significant visual damage. Fear not, by leaving the veins of your plants it allows them to get enough nutrients to survive the season. However, the unsightly appearance left behind is heartbreaking and will remain like so until the leaves fall off in the fall.

Their larvae, the current state they are in, are also desirable treats to many burrowing animals like squirrels and skunks. While it might sound like these animals are on your side, they will damage your garden further – tearing it up looking for a juicy grub snack. Although less visual, the damage left behind by the Japanese Beetles in their grub form is far more destructive to our lawns than the visual damage they do to our foliage.

Lifecycle of the Japanese beetle. Larvae feed on roots underground, while adults feed on leaves and stems.
Illustration by: Joel Floyd

The main problem for gardeners in Ontario is how resilient these beetles are to the safe and mild pesticides that are are left behind from the chemical ban in our area. Their thick and tough shells give them a protective armour that shields them from many convenient, easy to apply pesticides, so let’s attack them while they are in their most vulnerable, grub form, without their resilient outer shell.


Nematodes are microscopic, colourless worms that make their home in our soil. These varieties are dirt-dwellers that don’t bother humans, pets, or plants, but will attack an assortment of soil-borne pests instead. These hungry worms have a massive appetite for caterpillars, rootworms, gnats, grubs, and beetle grubs, amongst others. Nematodes’ hunger for destructive creepy-crawlies makes them an amazing solution to pest problems in our gardens.   

When a Nematode finds a host that they want to eat, they work their way inside them, where they start to eat their host with the help of powerful bacteria. A single nematode can kill a pest in 24-48 hours, making them a quick and efficient solution to infestations. The Japanese beetles targeting your garden might have a tough shell that we have a hard time fighting, but even they can’t stop the internal sneak attack from a nematode when they are in their grub form!

How to Use Nematodes in Your Garden

These microscopic worms are a great pest-fighting tool, so many people are eager to welcome them into their yards and gardens. While they are naturally occurring in many soils, if you are having a problem with pests you might not have them or not enough of them. Many garden centres offer packages of nematodes that you can release into your garden to boost your local population. They are stored in cool refrigerators to keep the worms dormant and ready to start fresh when they reach your soil.

Helping your nematodes do their work comes down to providing them with a good habitat to live in. Make sure you have warm and moist soil – the warmth keeps them awake and hungry, while moisture helps them move through the soil to find their next meal. So applying this army right after a rainfall or after irrigating your lawn is most effective.

If you are applying store-bought nematodes, you will find a sponge like sack in the package. Soak this sponge in water in a hose-end sprayer that has never been used for pesticides before to avoid killing the microscopic insect. Begin by spraying/drenching the affected area of your garden with treatment and allowing it to soak into the soil. As soon as your nematodes are fully awake, they’ll start sensing and hunting down their prey.

A common question is “how do I know when they have all been released from the sprayer?” Add a few drops of food colouring or a quick dip of a tea bag. When the colour of your water returns to its clear state you will know they have been successfully applied. Nematodes go where the food is so fear not, when they have devoured every unwanted insect in your garden, they will move onto the neighbouring yards.

Low-temperature scanning electron micrograph of soybean cyst nematode and its egg. Magnified 1,000 times.

Japanese Beetle Traps and Pesticides

Although there are many threads out there about the controversy of Japanese beetle traps, they prove to be very effective. Without the traps, these beetles will continue to multiply and take over our city’s beautiful landscape. Many people fear it will attract Japanese beetles from their neighbours’ yards but this trap uses a floral scent that can be found throughout your garden, whether it be on the trap or not.

The trick is to place this trap in the middle of your yard at least 10 feet away from any broadleaf plants you wish to protect. This will draw them away from your precious plants to the artificial, floral hormone acting as a trap. Make sure to pick up a few extra bag as you will be amazed how quickly these beetles will populate in the bag!


We already mentioned the lack of pesticides on the market, but after testing indoor and outdoor products in our own garden centre for the past four years, such as Doctor Doom’s Knockout Spray and BugTek, we have found some solutions that are very effective! Visit our garden centre when you notice their invasion and we will give you one-on-one advice for how to effectively get rid of this unwanted army.

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