Physical methods, including traps or hand-picking insects off of your plants, will destroy pests before they can cause extensive damage.
Patrol your garden with a bucket of soapy water, into which you drop insects you pluck off your plants. Spread a cloth or plastic sheet beneath your plants and shake insects such as beetles off your plants. Both of these techniques work best on cool mornings when insects are sluggish.
Water sprays are another effective nontoxic means of killing pests. The mere force of a strong spray of water will knock delicate aphids off plants and kill or injure them. Spray the underside of leaves with water from a powerful nozzle to wash off aphids and mite, and do so in the morning to avoid damaging foliage during the heat of the day.
Floating row covers are lengths of synthetic fabric that you drape over your plants as a physical barrier against pests. They allow more than 80% of sunlight to reach your plants, and pose no barrier to rain or irrigation. The microclimate under the cover is warmer and more humid, thus extending the growing season. Floating row covers provide season-long protection and are most useful for food crops. Drape them over your plants and bury the edges of the fabric in the soil, while allowing enough slack to allow for plant growth, or take the cover to a lightweight frame such as bamboo to allow for easy removal for weeding and other garden maintenance.
Collars are stiff cylinders constructed of cardboard or plastic that encircles plant stems at the soil level, acting as a physical barrier to such pests as cutworms. Fill the collars with wood ashes or diatomaceous earth to root maggot flies. You can make your own collars out of paper towel or toilet paper tubes. Encircle your seedlings as soon as you plant by pushing the collars into the soil.
Tree bands are barriers placed on the trunk of trees to prevent pests from crawling up the trunk. These work especially well for older gypsy moth larvae as they commute daily from the treetop down the trunk to hide in leaf litter during the night, and then climb back up the tree to feed during the day. Make a tree band by tying bands of cotton cloth or burlap around the trunk, with a string at the middle of the cloth, leaving the loose top section of cloth to flop freely as a dead end for pests. Regularly check your bands for pests and destroy them.
Copper is toxic to snails and slugs and an effective barrier against them. Wrap strips of copper around tree trunks or plant stems, or use copper edging to protect flower and garden beds.
Ants feed on aphid secretions and have been known to domesticate them, carrying them to establish an aphid colony that they then tend to and defend from predators. Simple inverted pie plates, with a hole corresponding in shape and size to the leg of a greenhouse bench, will prevent ants from reaching the table surface. Coat the underside of the pie plate with a tacky substance such as the commercial product known as Tanglefoot.
Dehydrating dusts destroy the waxy coating on the exoskeletons that protect insects from water loss. The resulting damage dehydrates the insects and eventually causes death, so many pests actively avoid them. To make your own, combine ¼ pound of diatomaceous earth with one teaspoon pure liquid soap such as Ivory, adding enough water to create a thick paste. Apply this as a ring around tree trunks to deter ants and many adult boring pests. For a garden application, spread diatomaceous earth, wood ash, or talc in a complete circle around the area you want to protect.
The best traps mimic the complex cues that insects use to find food or mates. They usually include a lure, such as a particular color or odor, and a physical trap, such as a sticky surface or a liquid such as water. Many sticky traps are yellow because that color attracts many species. Many flies will land on bright yellow sticky traps, as will gnats and aphids. Make your own by painting cardboard bright yellow paint. Long, rectangular or oval shapes are the most attractive to insects. Coat your traps with a commercially available product called Tangle-Trap, Stiky Stuff, or even STP oil treatment, but use caution, as these substances will be sticky to you too.
Bug zappers use ultraviolet light to attract and electrocute insects. They are indiscriminate however, and are as likely to kill beneficial species as they are to kill pests.
Pheromone traps release a substance that insects use to attract mates. These pheromones are placed within traps and the insects are lured to it. These traps are especially effective at targeting a single species of pest without harming other beneficial species. Pheromone traps are commercially available for a great many species of pest.
Baited traps use some form of bait to lure the insect in, usually a favorite food, or something that indicates the ideal conditions for laying eggs. Fermenting fruit attracts Japanese beetles while slugs prefer beer. Use potatoes for wireworms, or sprouting onions for maggot flies.
Part Four will wrap up organic insect control with non-toxic chemical options.
Chemical-Free Yard & Garden: The Ultimate Authority on Successful Organic Gardening, Fern Marshall Bradley, Editor