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The Coastal Gardener: Life-and-death garden struggles

June 03, 2010|Ron Vanderhoff

Not long ago, gardeners seemed to spend as much time controlling pests as they did any other garden activity. Malathion, diazinon, Dursban and chlordane were about as popular as marigolds, dianthus, dahlias and chrysanthemum.

It's nice to see that gardeners have evolved a much more laissez-faire approach to the six-legged inhabitants that share our gardens. Maybe gardeners today are just too busy, or maybe they're just not paying as close of attention as they used to, but there seems to be a lot less spraying, dusting, baiting and generalized killing going on in gardens nowadays.

But mostly I think that gardeners are now realizing that in a healthy, well-managed garden, some pests are best controlled by letting things be, by letting species interactions run their course. After all, this is the basis of biological pest control.

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Biological control agents are often referred to as natural enemies or simply as beneficials. Every day, in every garden, there is a continual interaction between pests and their predators, parasites and pathogens. Most of this interaction we, as gardeners, don't participate in and may not even be aware of.

So why is there significantly less use of pesticides today than there was 10 or 20 years ago? Certainly there are no fewer pests.

Let's look at the example of one of our most abundant garden pests, the aphid. Five possible things can happen to an aphid in a garden, four of which are bad for the aphid but good for the gardener.

First, they could become mummies. Aphid mummies are the little crispy, golden, puffy-looking, empty aphid shells that we sometimes see stuck on leaves and stems. These golden husks are not the molted skeletons of growing aphids, but are the parasitized remnants of unlucky ones. Insect parasites make a living at their host's expense, coexisting with the host, at least for awhile. After all, killing the host would be counterproductive and leave the parasite with no place to live and pupate. This is why parasitic insects, especially many small flies and wasps, are good garden allies.

Elsewhere, a different aphid is having another type of bad experience. Ladybugs seem to be constantly hungry and soft, so slow-moving, dim-witted aphids are a favorite breakfast, lunch and dinner. An adult or larval ladybug can eat hundreds of aphids in a day. Other predators, like lacewings, soldier beetles, syrphid flies and several true bugs are in the garden, too, searching for a tasty aphid meal.

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