Pest, Meet Predator

There are two types of garden insects: the bad and the beneficial. Bad bugs, such as aphids and weevils, are nature’s pests because they can destroy plant life. Beneficial bugs are pollinators (such as bees), and predatory or parasitic insects that prey on the bad bugs. Both are integral to earth’s ecosystems, including the one in your own backyard. So the next time you’ve got a pest on the premises, match it up with a predator and let nature do its work.

Grubs vs. Nematodes

The pest: Grubs (white C-shaped worms) are the larvae of a group of beetles that feed on grass and plants roots from spring through summer, leaving brown splotchy patches in their wake.

The predator: Nematodes are microscopic worms that tunnel through the soil, seeking out grubs for food. There are thousands of varieties, but several that are native to Canada are particularly effective at controlling insects that affect your lawn: Heterorhabditis bacteriophora is particularly grub-hungry, but there are other kinds of nematodes in soil, such as Steinernema carpocapsae, which can be used for surface insect control. 

Improve the odds: While nematodes live in lawns that have not been treated by pesticides, they don’t always exist in sufficient quantity to do the job. Fortunately, you can purchase them at garden centres, or through a lawn care specialist. A safe, effective douse of these beneficial nematodes will kill grubs within a few days. They will then move on in search of other insects, and will eventually die off when they are no longer able to find food.

Aphids vs. Ladybugs

The pest: Aphids, also known as plant lice, are small (less than two millimetres long) green, beetle-shaped insects. They use their needle-like mouth to suck sap from vegetable plants, shrubs, flowers and ornamental trees throughout the year, thereby slowing growth, wilting leaves, drying branches and damaging foliage.

The predator: Fortunately, one of the ladybug’s favourite foods is the aphid. The notorious red-and-black spotted beetle also munches on mealy bugs and spider mites.

Improve the odds: Yarrow (Achillea spp.) and scented geraniums (Pelargonium) attract ladybugs. You can also purchase ladybugs at a garden centre: just make sure they’re locally sourced. Release them into different places in your garden over two days. If they don’t stick around, don’t worry—it probably means there wasn’t enough food for them in the first place.

Tomato hornworms vs. Braconid wasps

The pest: Large, green tomato hornworms are the larvae of the Five-Spotted Hawkmoth, and they love to dine on the leaves and fruit of your prized tomato plants in May and June. (They eat enough foliage to grow three to four inches long!)

The predator: You can pick the hornworm off your plant, but dark Braconid wasps will take care of the problem naturally. This parasitic insect lays its eggs right on the hornworm, and its larvae then consume the host. Don’t remove hornworms that have tiny white cylindrical protrusions—an indication that the wasps have already found an unwitting host. Left to mature, the Braconid wasps will multiply and continue their good work.

Improve the odds: Attract parasitic wasps to your garden (they will also help control aphids and caterpillars) with plants such as Sweet Alyssum (Lobularia maritima), Allium (Allium sp.), Queen Anne’s lace (Ammi majus) and Purple Poppy Mallow (Callirhoe involucrata).

Weevils vs. Ground beetles

The pest: The larvae of Black Vine weevils overwinter in the soil, then cause serious damage to evergreen trees and shrubs in the spring, when mature weevils (10-millimetre-long, oblong-shaped with a dull, slate gray to brownish black colour) emerge to feed on foliage. They also love rhododendrons.

The predator: Ground beetles have quite an appetite for weevil eggs, larvae and even adults. (Nematodes species—Heterorhabditis bacteriophora—will also hunt down weevil larvae and infect them with lethal bacteria.) Don’t confuse these big, black, slightly iridescent helpers with June beetles—another garden pest—which are much bigger.

Improve the odds: Create a healthy predatory ground beetle habitat by spreading a  five-to-eight centimetre layer of mulch around the base of woody plants and perennials, and accent your garden with a rock or log where they can take shelter.

For natural lawn care supplies and advice, visit the “Gardening and Landscaping” sections of the Green Living Guides.