Avoiding Pests and Disease

Broad-spectrum insecticides backfire because they destroy beneficial insects as well as problem pests, and as a result, they upset the natural balance of bugs in the landscape. It's the balance between good and bad bugs that's critical to achieving the biodiversity that allows both kinds of insects to coexist.

"In other words, it's okay to have bugs that prey on your plants as long as you also have bugs that prey on them," he says. "When--and only when--the population of problem pests gets out of control should you even consider control measures, and even then, you might want to think twice before spraying or dusting."

The population of beneficial insects can't rebound at the same rate of problem pests. Nature designed the system that way to make sure there would always be an adequate food supply--or plant-eating bugs for the beneficial insects to consume. So if, for example, you spray a broad-spectrum pesticide on a plant plagued by aphids, you may actually do more harm than good. You might destroy 80 percent of the aphids, but you would almost certainly destroy 100 percent of the lady beetles that were busily eating all those aphids. And what's more interesting is that aphids don't have to mate during the growing season. In fact, female aphids are likely carrying unborn females that are already pregnant. The lady beetles, on the other hand, are at a distinct disadvantage. They must find a mate and reproduce in the more familiar sense, which takes time. And in the meantime, the aphids have a huge jump-start on whatever plant you've just sprayed.

Insects can and very often do develop a resistance to certain garden chemicals, and the results of such genetic resistance can be even more devastating. Each time you apply a pesticide, a few pests will survive. In the next generation that they produce, the offspring may develop a genetic resistance to that pesticide. And genetic resistance can occur very quickly in the insect population because insects are capable of producing many generations over a short period of time. In mammals, genetic changes may take thousands, perhaps even millions, of years.

"This is all reason enough to avoid the use of garden chemicals," James says, "but I am willing to admit that there are times when you need to control pests." He offers some tips: