The first step in dealing with garden insect pests is identification. Most insects found in gardens are not pests--in fact they may be predators of pests. Too often gardeners assume that an insect found on a plant is a pest, when this may not be the case. Identification is not difficult. A small field guide, such as "Good Bug, Bad Bug" by Jessica Walliser (St. Lynn's Press, 2008) makes it clear which insects are your enemies and which are your friends.
Just because an insecticide is classified as "organic" does not mean that it is harmless to humans, pets or beneficial insects such as honeybees. Read and follow package instructions carefully.
Certified organic growers, who are subject to the rules of the U.S. Department of Agriculture's National Organic Program (NOP), can only use substances that have been approved by the Organic Materials Review Institute (OMRI). Since there are many substances on the market that claim to be "natural" or "organic," it is worth looking for the "OMRI LISTED" seal on the label of a product. This is the only assurance buyers have that a material meets strict NOP rules.
This is one of the safest insecticides. It is made from plant oils and animal fats, and works by penetrating the outer shells of soft bodied insect pests. This causes dehydration and death within hours. It is effective against aphids, mealybugs, spider mites and whiteflies, but does not kill beneficial insects such as ladybugs, praying mantis or other beneficial insects with a hard exoskeleton.
There are several products on the market that contain neem oil. Compounds in neem oil discourage insects from feeding on treated plants. Some insects will starve rather than eat plants treated with neem. If it is ingested, neem can disrupt insects' molting and reproductive cycles. It is non-toxic to birds, mammals and beneficial predators like ladybugs, spiders, bees and wasps.
This superfine oil works by physically smothering insects and their larvae. It can be used year-round on trees, evergreens, ornamentals, flowers, vegetables and houseplants. The entire plant, whether it is a large tree or a small houseplant, has to be totally covered with the oil for it to be effective--every nook and cranny in the bark, and the top side and underside of every leaf.
Particle Film Coating
Surround WP is the brand name for a product made with kaolin clay, a natural mineral. It covers the leaves and fruit of a tree or other plant with a rather ghostly looking white particle film coating, which suppresses feeding by a wide range of pests, especially those that damage fruit crops. The nontoxic coating is easily removed from fruit and produce before eating.
Commonly abbreviated as Bt, Bacillus thuringiensis is a species of insect-specific bacteria that has been developed as a microbial insecticide. Bt is not a contact insecticide. It has to be consumed by the target pest to become effective. There are four varieties of Bt in use: Bt var. tenebrionis, which is effective against Colorado potato beetle and elm leaf beetle larvae; Bt var. kurstaki, which is used to target caterpillars (many of which are important farm and garden pests); Bt var. israelensis, used against mosquito, black fly and fungus gnat larvae; and Bt var. aizawai, for wax moth larvae and some caterpillars, especially the diamondback moth caterpillar.
Other Organic Insecticides
There are several other insecticides that are derived from natural substances. Rotenone is derived from the roots of tropical plants. Pyrethrin is a powerful and dangerous insecticide extracted from the roots of a type of chrysanthemum. Sabadilla is another highly dangerous pesticide, derived from the seeds of a lily found in Central and South America.