Before chemical pesticides existed, gardeners managed to control insects with what we today call "alternative methods." While alternative methods of controlling insects may be more labor intensive, they can be effective. Some damage will occur, and your garden may not appear perfect; however, the goal of chemical-free gardening is to provide a healthier and safer garden environment.
Beneficial Predatory Insects
Learning to identify beneficial insects is important in a chemical-free garden. Many pests have natural predators that can be used as a means of control. Most organic gardeners are familiar with using ladybugs or lady beetles to control certain pests, but there are many other predatory species that can help control insects in the garden.
According to the Cornell University Biological Control site, there are predatory and parasitic insects for control of a wide variety of plant and garden pests. Lebia beetles are a natural enemy of the Colorado potato beetle. Rove beetles attack eggs, larvae and pupae of root maggots and are especially effective against the cabbage and onion maggot.
Lacewings are important in interior plantscapes and greenhouses as a predator of long-tailed mealybug. They are used in exterior landscapes for the control of aphids, whiteflies and spider mites. They also prey on eggs of tobacco budworm, beetle larvae, leafhoppers, small caterpillars, moths and leaf miners.
According to Cornell University, 19 species of parasitic wasps and flies attack the larvae and adult forms of caterpillars, ants and plant bugs.
Bacteria and Baculoviruses
Bacillus popilliae is a milky spore bacteria that is used exclusively to control Japanese beetles. A more commonly used bacteria, Bacillus thuringiensis (BT) is approved for use in the home garden for caterpillar control.
Baculoviruses are found everywhere insects live. Many baculoviruses are insect specific and are sold for control only on certain crops. Baculoviruses are used for control of codling moth, cabbage moth, American bollworm, diamondback moth, potato tuber moth and grape berry moth. They are also effective against tobacco budworm, beet army worm, celery looper, alfalfa looper, Douglas fir tussock moth and gypsy moth.
Inert dusts are divided into four groups: synthetic silica aerogels, clays and ashes, minerals and diatomaceous earth (DE).
Inert dusts work by damaging the waxy outer layer of the insect's body, leaving it susceptible to dessication (drying out) and death. They are effective against hard-shelled insects, such as beetles and ants. The two inert dusts used most often are diatomaceous earth and silica aerogels.
Insects such as aphids and spider mites can be controlled by washing them off the plant with a strong spray of water. They will likely return to the plant, and this is not practical if there are a large number of plants to treat. For plants prone to these insects, a daily spraying is a preferred method of control for organic gardeners.
Hand picking insects and caterpillars from plants is an option that is often included along with other methods of control. Hand picked insects are usually disposed of in a container of soapy water.
Homemade Soap and Oil Mixtures
A mixture of soap, oil and water can be effective against soft-bodied insects and even against some beetles if they are sprayed directly. Only spray soap or oil mixtures on plants during early morning or early evening hours to avoid burning the plant.
The University of Florida Extension Service recommends a mixture of 2 tbsp. dishwashing liquid without degreasers added (not automatic dishwashing detergent or laundry detergent) plus 2 tbsp. vegetable cooking oil in 1 gallon of water. Spray plants at weekly intervals.