Allies in the Battle to Protect Your Precious Plants

Birds, beneficial insects and other predators help control garden pests

06-01-1996 // Michael Lipske

Gardening brings to mind tranquil days outdoors in the midst of nature, the steady progress of the seasons, the joys of the harvest. But for many homeowners, it can also closely resemble jungle warfare. Warfare? In your garden? "Only in the sense that your every effort to grow flowers or fruits and vegetables can be undone by a horde of hungry enemies," says Craig Tufts, manager of the National Wildlife Federation's Backyard Wildlife Habitat Program. Aphids, caterpillars and other plant-eating "thugs" seem to lick their chops at the sight of a lush garden.

Tufts does not panic over aphids and other pests in his Virginia garden, however, because he knows that he needs some of them around to feed predators like ladybird beetles. Without some pests in his yard, Tufts would not attract these predators, which means that in late summer he could become overwhelmed with such pests. "With a good group of predators around, I'll have one-tenth or one-twentieth the number of aphids I would otherwise have," he says.

The goal, observes Tufts, is garden equilibrium. "Create a well-balanced garden," he says, "that will attract equal numbers of predators and prey."

Often, nature will rein in pest populations. But if garden pests do become temporarily overwhelming, gardeners can regain the upper hand through biological control, which simply means turning to a host of natural, predatory allies in the battle against damaging insects. Why put your faith in bug-to-bug combat when chemical pesticides seem to do the job more quickly? Because spraying poisons, aside from the danger they pose to birds and other desirable wildlife, is only a short-term fix. Poisons kill not just pests but pest-eating bugs. And more often than not, the pests rebound first. "Almost always, predators take a longer time to come back," says Tufts. "In the meantime, your pest problems have returned."

Songbirds are one form of biological control. Create a backyard habitat that provides them with water, some favorite food plants and places to hide and to rear young, and you should be well rewarded for your effort during spring and early summer. That is because during nesting season, 90 percent or more of the food that parent birds give to their young consists of other creatures, for the most part insects. Toads and frogs are also voracious bug eaters. A small, shallow pool added to your yard can provide a breeding place for amphibians.

In the long run, insect allies may be your most formidable weapon for slaying insect pests. Praying mantises, for example, are effective backyard plant protectors. You can increase your mantis population by collecting their eggs in winter. Visit a local field and look for dirty-white egg masses (they resemble plastic foam) mantises have stuck to plant stems. Clip the stem along with the egg mass and put it in your yard to hatch in spring.

Mantises are impressive, says Tufts, "but some of the smaller insects are going to do the best job for us in our gardens." Ladybird beetles and lacewings are particularly efficient predators. You can buy them from mail-order garden catalogs to release in your yard, but you are better off providing the sort of habitat that naturally encourages respectable numbers of these creatures. "Good clean food sources," says Tufts, meaning backyard bug populations that have not been doused with chemical pesticides, attract not just ladybugs and lacewings but other predators, such as the aptly-named assassin bugs. Insects that eat other insects also spend time dining on pollen. Tufts advises planting early blooming flowers and shrubs (as well as trees like alders and birches) to boost your pollen production in spring. That should lure insects which, come summer, will turn their jaws against their fellow bugs. "By producing a diverse habitat, in terms of lots of different types of plants that bloom at different times, you're going to encourage the greatest number of predators into your yard from local populations," he says.

To help you distinguish good bugs from bad, get an insect guidebook, especially one that shows how larvae as well as adults look. Larval predators are often more voracious than adults. Ladybug larvae (gray-purple lizardlike things that crawl up and down plant stems, notes Tufts) are aphid gluttons. Hoverfly larvae are predatory maggots that also wreak havoc on aphids.

According to Tufts, other ways to control problem bugs biologically include:

  • Plant fennel, dill, goldenrod or tansy to attract parasitic wasps that lay their eggs on insect pests. Most of these wasps are tiny and stingless—thus no threat to backyard barbecuing. The adults feed on pollen (hence the need to provide flowers), but their young require other insects in order to go through metamorphosis. Aphid-mummy wasps are so small they lay one egg per aphid. The parasitized pest sustains the wasp's offspring and dies doing so.

  • Support your local spiders by not destroying their webs. Orb weavers--spiders that spin large, handsome webs—are highly efficient predators of crickets, grasshoppers and moths.

  • To control grubs that damage everything from carrots to turf grass, consider using parasitic nematodes. These are tiny worms that, in their larval form, can help control a variety of plant pests. Available from mail-order firms that sell organic garden products, the nematodes work underground, where they invade the bodies of grubs. These killer worms (which pose no danger to humans) release bacteria into their insect host. The bacteria kills the grub, and the nematode feeds on the victim.

"These creatures may seem like they're straight out of a science fiction novel," says Tufts, "but there's nothing fictional about their effectiveness." Indeed, nematodes are one more weapon available to gardeners who find themselves in the midst of jungle warfare.

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