Bug Wars

It's not that I'm a pacifist. My fingers know quite well what it feels like to squash Mexican bean beetle eggs on the undersides of bean leaves. A few too many leaning towers of Japanese beetles on anything calls for a swift kick into a pail of soapy water; pyrethrin takes care of some too. My husband and I leave every wasp nest undisturbed and even escort the occasional wasp out of the house so that it can go back to work in the garden. And chemicals come out on occasion—when the problem is big, involves a dearly beloved tree or crop, and when mechanical or cultural means are of little use. But then I try to target the specific pest (or disease) and do as little harm to other critters as possible.

A lot of times, gardeners know, the best course is to not reach for the bug spray but to keep plants healthy. A plant that's well-sited and cared for—getting the type of climate, soil and light it craves, and receiving neither too much nor too little water or fertilizer—is more resistant to attack. Having lots of different species in your landscape, rather than just a few, helps reduce the likelihood that a massive infestation will occur. Not using broad-spectrum insecticides too soon and/or willy-nilly helps keep your allies—the good bugs—healthy. And if you want to hedge your bets even further, avoid planting pest-prone species altogether.

Sometimes infestations are self-limiting. Left to her own devices, Mother Nature often finds a way to balance things out. The Eastern tent caterpillar tends to go on an eating binge for a couple of seasons, but its M.O. as a tree-defoliater comes to an end in an area when a particular virus moves in and wipes it out. As you well know, though, you can't always depend on the rescue arriving in time. How does the gardener know when to intervene in the bug wars?

How do you know when to intervene in the garden? "It depends on your objectives," says Cliff Sadof, extension entomologist at Purdue University. "In terms of plant health, a 10% loss in foliage is completely insignificant. You can lose 25% of leaves in apple trees and have it not affect yields. But a 50% defoliation can harm plant health."

The other element is timing, says Sadof. "If it occurs early in the year, when the leaves are not fully grown and the plant hasn't fully invested its resources into leaf development, it's not that big a deal. When you lose leaves three to four weeks before they would normally fall off, it's not a big deal. But in the middle of June, say, when leaves are older, a 50% defoliation can really harm the plant's health."

First and foremost, identify the pest. If, as is so often the case, the bug you see doesn't match up to anything you can find in a reference book, take it to your local extension office (or you may be able to e-mail a photo of it). If you don't see a bug but you do see damage, take in a cutting of that damage. The problem could be a tiny bug—or maybe not even a bug at all. In about half the cases, the problem is a cultural one—water, climate or location.

Photos courtesy of Drees, Texas A & M University.