Organic farming attempts to restrict the use of synthetic pesticides, growth hormones and genetically modified plants in an effort to produce healthier food and do less damage to the natural environment. The U.S. Department of Agriculture maintains a registry of acceptable insecticides for trees bearing fruit that may legally be sold as organically grown; the labels of commercial insecticides purporting to be organic should say if they are registered by the USDA.
Organic insecticides are derived from plants, naturally occurring minerals and biological sources. The major organic insecticides derived from plants are pyrethrin, derived from the pyrethrum plant (Chrysanthemum cinriaefolium); extracts from the neem tree (Azadirachta indica); nicotine sulfate, extracted from tobacco; sabadilla, derived from the seeds of the sabadilla lilly; and rotenone, extracted from the roots of jicama and related tropical plants.
Two major organic insecticides are made from minerals. Sulfur comes in the form of dusts, liquids, powders and paste; lime sulfur is made by boiling lime and sulfur.
Bacillus thuringiensis, commonly called BT, is the most often used biological organic insecticide. It is a bacteria produced in the guts of moths and butterflies.
Pyrthrin will kill most insects; it knocks them down quickly, but many recover, so it is often used to flush insects out so they can be identified. Neem is often used in a horticultural oil that is sprayed on trees when they are dormant; it stops insects from laying eggs and prevents them molting so they never mature. Nicotine sulfate kills aphids, thrips, spider mites and other sucking insecticides. Sabadilla kills caterpillars, stink bugs, squash bugs, leaf hoppers and thrips. Rotenone stops insects from feeding.
Sulfur sprayed on trees will kill insects that suck sap, including spider mites and thrips. Lime sulfur will kill eriophyid mites, scales and thrips.
Bacillus thuringiensis works best against the caterpillar larvae of leaf rollers but does not work as well against caterpillars that feed on the fruit, including the codling moth and oriental fruit moth.
Organic insecticides generally do not act as quickly as more toxic synthetic insecticides. Insecticides in the form of horticultural oil are preventative; they block infestations of harmful insects. Neem suppresses infestations over a period of weeks. Rotenone takes several days to kill insects.
Organic insecticides are used when the grower wishes to have healthier fruit that is certified as being organically grown. While organic insecticides are generally less effective than more toxic, fast-acting synthetic insecticides, they are generally safe to handle and to use if children or pets are around; they generally only kill targeted insects, not beneficial insects. They break down quickly and do not remain in the environment as toxins. Many organic insecticides can be applied up to the time fruit is harvested.
While most of organic insecticides do not harm humans, they should not be inhaled or ingested. Insecticides containing sulfur can burn the skin and eyes. Gloves should be worn when handling sulfur. Sulfur can harm plants if it is applied in dry weather more than 90 degrees F; it should not be used with other pesticides or within 20 to 30 days of spraying trees with dormant oils.