One of the easiest ways to use natural pest control in your garden is to protect and encourage such natural allies as birds, toads, spiders, nonpoisonous snakes, and insects that feed on other insects.
In many cases this simply involves no more than tolerating the predator (such as a snake or spider) instead of killing it or destroying its habitat.
With a little more effort you can provide suitable habitats for insect destroyers; for example, an inverted flower pot for toads or a special birdhouse for purple martins.
Another solution for natural pest control is to stock your garden or orchard with beneficial insects. Ladybug and praying mantis eggs are sold by many garden supply houses; both insects prey on a variety of common pest.
Another natural predator is the trichogramma wasp, which lays its eggs inside the eggs of many species of caterpillar. The wasp larvae feed on caterpillar eggs, destroying them.
The introduction of specific insect diseases is a proven biological method of pest control. Milky spore disease, available as a white powder, can be dusted on the soil to infect and kill the larvae of the Japanese beetle.
Bacillus thuringiensis, BT for short, is a bacterium that infects many destructive caterpillars, including the cabbage worm and gypsy moth.
It is applied as a spray and has an effective life of seven days. Both milky spore and BT are harmless to humans, domestic animals, and such beneficial insects as honeybees.
More sophisticated biological controls have been developed, although as yet they are practical for large scale use only and are therefore beyond the scope of the home gardener. One such method is the rearing and release of huge numbers of sterile male insects.
By competing with normal males in mating, these sterile insects reduce the number of offspring.
Another technique is to spray caterpillars with juvenile hormones; the caterpillars never mature to have young, cutting down tremendously on the size of the next generation.
So called trap crops take advantage of the food preferences of various insect pests by luring them away from more valuable crops.
For example, naturtiums lure aphids away from nearby vegetables, while Japanese beetles are attracted to white geraniums, white or pastel zinnias, and odorless marigolds.
Radishes lure root maggots away from cabbage crops, eggplants draw flea beetles away from potato plantings, dill attracts tomato hornworms, and mustard greens are a good trap crop for harlequin bugs.
Pests concentrated on the trap crop can be picked off by hand and destroyed, but this must be done regularly or the trap crop will not be effective. Kill the pests by dropping them into kerosene or into water that has a thin layer of kerosene on it.