by Erin Hynes
The garden version of biological warfare can be pretty appealing to gardeners who don't want to use pesticides in the garden — even organic ones. Instead, unleash a living foe of the pest insect and let nature take its lethal course.
These foes are known as biological control agents — that's any living thing, such as birds, spiders, diseases, nematodes and insects, used to control garden pests.
You can buy biological controls for the home garden, but do they really do the job? Some do, but some are a waste of money. Here’s a run down on popular biological methods for the home garden and how well they work.
Bt for Caterpillars
The bacterium Bacillus thuringiensis var. kurstaki has been around for decades for controlling caterpillars including gypsy moth larvae, loopers, leaf rollers, horn worms and tent caterpillars before they hide in their tents. It’s deadly for caterpillars that ingest it as they dine on leaves, but safe for mammals, birds, reptiles and fish — actually, for any creature with acid in its gut.
Bt is widely available under several brand names and is effective if applied where actively feeding young caterpillars will eat it. The downside is that Bt also kills caterpillars that turn into butterflies, and many butterfly populations already are at risk.
Your best bet. To protect butterflies, use Bt only when a heavy infestation threatens a plant that's expensive to replace. For controlling inchworms on your lettuce, it’s not worth the risk. Instead, pick off caterpillars or spray with insecticidal soap.
Bti for Mosquitoes and Black Flies
The bacterium Bacillus thuringiensis var israelensis controls black flies and larval mosquitoes in standing water. it doesn't control adults.
Your best bet Use it if you have a still body of water nearby. If not, reduce mosquito numbers by getting rid of standing water — clean your gutters, dump out buckets of water, and empty and refill birdbaths often.
Milky Spore for Japanese Beetles
As any homeowner east of the Mississippi can tell you, the adult Japanese beetle vigorously feeds on a variety of ornamental plants, and seems especially fond of roses. The soil-dwelling C-shaped grubs of Japanese beetles — the larvae — eat the roots off the lawn. You have two biological options:
- Milky spore disease is a bacterium, Bacillus popilliae, that kills the grub form only. It’s widely available, but effectiveness is iffy because it doesn't harm adults already in your yard or that fly over the neighbor’s fence. And Japanese beetles seem to be developing resistance to it. Even when it does work, it takes weeks to kill the larvae, who continue munching turf roots in the meantime. Cornell University’s biological control website goes into the topic in detail.
- A more effective control is a nematode — a microscopic roundworm — called Steinernema kushidai. It's fast acting and very safe for humans and pets. Unfortunately, it's not yet available commercially.
Your best bet If you have a large piece of land and wish to take on the expense of treating with milky spore disease, it might be effective. In an average-size yard, cover valuable plants with floating row covers during the 4 to 6 weeks the beetles are active. Shake those sitting on plants into a bucket of soapy water or pick them off by hand.
Ladybugs for Aphids and Scale
Hundreds of species of ladybugs — also called lady beetles and lady bird beetles — prey on aphids, scale and mites. Both the adults and the larva, which are called aphis lions and look like tiny alligators, are beneficial insects. Ladybugs are active from spring through fall and can eat hundreds of aphids a day. (The ladybug that invades homes in autumn is just one species, the multicolored Asian lady beetle. Don't let it give all ladybugs a bad name.)
You can buy ladybugs to release in your garden, but unless you have a robust population of aphids for them to feed on, they'll fly off.
Your best bet. If your garden is infested with pests ladybugs eat, ladybugs will find your yard. Encourage them by not spraying your garden with insecticides. And learn to recognize aphis lion, so you don't mistake them for a pest. If you can't wait for ladybugs to devour an aphid infestation, hose the aphids off the affected plant or slip off the affected part and drop it in soapy water.
Parasitic Wasps
Tiny wasps inject their eggs into a host insect; the hatched offspring feed on the innards of the host, killing it. Many species are available commercially for controlling specific caterpillars, aphids, beetles and scale.
Your best bet. Consider buying them if you run a commercial orchard or far. Otherwise, invite parasitic wasps to your garden by growing a variety of nectar-producing flowering plants, especially mints and daisies. Don't use pesticides. Learn to identify infested caterpillars and then leave them alone so the young parasites can live long and prosper.
Pheromones and Hormones
Pheromones and hormones are biochemical methods, not biological, but they merit mention because they're sold for controlling insects. These attractants lure pests such as coddling moths into traps hung on trees. They seem effective because the traps do indeed fill up with insects. The problem is that the traps attract pests from far and wide that find your yard but not the trap.
Your best bet. If you have a commercial home orchard or farm, use traps to alert you to when pests arrive and to get a sense of their populations. In the home garden, don't bother. However, if you have grain moths inside your home, traps can be effective.
Erin Hynes has written several books about organic gardening. She holds a masters degree in Weed Science from Penn State.
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