Controlling Japanese Beetles, Aphids, Ants, and Caterpillars


The garden is a true Wild West of critters. From friendly pollinators, like leafcutter bees, to the despised Japanese beetle, we plant enthusiasts are forever trying to maintain a natural balance between the good, the bad, and the ugly. 

Sometimes, when pests step out of line, we need to intervene to keep our plants safe. The following pests are the ones Guelph gardeners ask us about the most. Here are our tips on controlling the region’s toughest pests, without causing too much collateral damage.


How to Control Japanese Beetles

Japanese beetles are a growing problem in Guelph. These exotic-looking pests got here by hitching a ride in the baggage of tourists a few decades ago. With tough outer shells and no natural enemies in North America, they’ve gotten to be a huge nuisance to control. Here’s how to tell if you have a Japanese beetle problem on your hands.

Spot the Pest

Japanese beetles are part of the scarab family of beetles. They have iridescent green abdomens and metallic copper wings, and the sides of their bodies are lined with small black and white hairs. It’s a bit of a shame that they’re such pests because they’re really quite interesting to look at.

It also bears noting that adult Japanese beetles are not the only threat to your landscape. Japanese beetles lay their eggs in lawns, which hatch into the White Grub, a small white c-shaped larva, that feasts on grass roots.

Spot the Damage

The larvae feed off grass roots as they mature. By the time they’re ready to fly away as adults, they’ve left patches of weak, brown grass that pull out easily from the soil. 

As adults, Japanese beetles target plant leaves, eating between the leaf veins. Their telltale damage leaves your once-beautiful foliage looking like a skeleton of its former self.

Getting Rid of Japanese Beetles

While you can use baited traps to catch Japanese beetles, you may unintentionally attract more than you catch. There are a few approaches you can combine to protect your yard. 

To break the cycle of infestation, try introducing beneficial nematodes into your lawn soil. These microscopic parasites are harmful to the grubs but not to you or your pets. Ask us at our garden centre which nematodes work best for your beetle problem.

To prevent further damage to your plants, you can set up a Japanese Beetle trap, which we carry here at the garden centre. Since they’re nearly impossible to kill in the adult stage, the next best thing is removal. These traps use pheromones and floral lures to entice the beetles into a bag or box where they become trapped for easy removal. 

Finally, if you don’t have a trap, you might have to do some hunting to control an active infestation. Visit your plants in the early morning, while the cold-blooded beetles are still sluggish from the cool air, and pick them off. You can also shake plants over a bucket of soapy water, which will drown them quickly.


How to Control Aphids

Aphids are an extremely common garden pest, and we all come across them sooner or later. While the damage they leave is unsightly, aphids are still an important part of the natural ecosystem. I prefer to opt for natural methods of controlling these little guys.

Spot the Pest

If you’re not already acquainted with aphids, they’re small, sesame-seed shaped pests that can be either green, tan, brown, black or look like a cotton ball. . They may or may not have wings. They tend to hang out on the underside of plant leaves. You may also notice spots of a shiny, sticky residue called “honeydew” that aphids leave behind on the surface of plant leaves.

Spot the Damage

Aphids feast on the juices in your plants’ foliage. You’ll notice your plants developing yellow, discoloured spots where the aphids have sucked out their chlorophyll. Over time, a severe aphid infestation can leave a plant looking pretty sick.

Getting Rid of Aphids

Beneficial insects are highly effective for controlling aphids. Introduce ladybugs into an infested area of the garden—both the adults and their larvae are voracious aphid hunters. Praying mantis is also a keen hunter, but be careful with them. They tend not to discriminate between aphids and friendly pollinators when hunting for a snack.

If your beneficial insects aren’t cutting it, try spraying affected plants with an insecticidal soap solution. Spray your plant three times, each three days apart to ensure you hit all the life stages of the aphid.  Insecticidal soap lasts a very short time on the plant to avoid interrupting the life cycles of beneficial insects.


How to Control Ants

Ants themselves are actually pretty effective pollinators, so if you only spot a couple, it might be easiest to live and let live. However, giant anthills forming in the middle of your lawn might be cause for concern. Another strange phenomenon is that ants have a bit of an allyship with aphids. Ants seem to like aphids and farm aphids the same way we farm cattle. (Apparently, ants are attracted to their honeydew, or maybe aphids look like dogs to them.) Ants might actually try to protect aphids from their predators. In that case, the ants have to be put in their place.

Spot the Pest

You’ve seen them. Little guys with three distinct body sections, antennae, and quick little legs. They’re usually reddish, brown, or black.

Spot the Damage

Ants don’t really damage your plants per se, but their colonies can cause the grass above to get very sparse. The problem with ants is their sheer numbers. When a colony is nearby, they’ll start to infiltrate your yard and maybe even find a way inside your home.

Getting Rid of Ants

The most effective solution to control ant colonies is to mix up a cup of sugar and a cup of Borax and sprinkle the mixture over top of the colony. This will encourage the ants to bring the Borax deep into the colony, where it will poison the Queen and the ants around her. The colony will quickly die off.

If you don’t necessarily want the ants to die, but you’d prefer they set up shop elsewhere, sprinkling black pepper or cinnamon on the anthill can encourage them to get out of Dodge.


How to Control Caterpillars

Before we jump into it, let’s just remember that without caterpillars, we can’t have butterflies. If caterpillars are becoming an issue in your garden, I strongly recommend taking a gentle approach. We don’t want to be throwing the baby out with the bathwater by threatening some of our most beloved pollinators.

Spot the Pest

Caterpillars come in an endless array of colours, sizes, shapes, and textures, but they all tend to munch on leaves. You might notice the eggs before you notice the bugs. They tend to be stuck on to the backs of plant leaves.

Spot the Damage

Caterpillars tend to eat the outside edges of leaves or random holes on the inside of the leaf area, as opposed to beetles who tend to work between the veins. Check on plants that show damage daily to spot any new eggs on the backs of the plants.

Getting Rid of Caterpillars

If the damage you find is just a little bit here and there, my advice is to let it be. Consider it a donation to the “butterfly foundation!” However, if you’re routinely having your garden ransacked by caterpillars, try companion planting to discourage butterflies and moths from laying eggs on your vulnerable plants. Mugwort, lavender, peppermint, and sage are natural repellents to these insects. Plant a few in the area to keep them away.

If you see a caterpillar tucking into your favourite plant, just move it! Use rubber gloves (some caterpillars have ways of defending themselves—better safe than sorry!) and place it down outside of your yard.

If you see eggs on a leaf, pluck the leaf off and move it away from your garden.

If you absolutely must control the numbers of caterpillars in your garden and for some reason cannot use live control methods, use diatomaceous earth. Sprinkle the powder around the plants in your garden. The product uses no poisons but the jagged particles cut up the skin of soft-bodied insects like caterpillars, cankerworms, and cutworms.

These pests may be “Guelph’s Most Wanted,” but there’s no need to go full-on armed and dangerous. While we’re right to nurture our favourite garden plants, we must also remember that the garden is their natural habitat, and we can do more harm than good by bombing the area with harsh and unnecessary pesticides. When controlling garden pests, the best approach is one that aims to restore equilibrium to the ecosystem. Nature will do the rest.