Ever since the institution of the Neighbor Notification Law, there have been a lot of tree care companies that claim that they apply only "Organic", "Bio-rational" or "natural" pesticides.
The differences between conventional pest control programs and organic or natural programs, is not just the choice of materials, but in the whole philosophy that surrounds the treatments.
Conventional outdoor pest control is largely reactionary; responding to insect pressures after they have become established with pesticides designed to kill the specific insect present. Your normal program will consist of anywhere from 4 to 9 treatments per year, each targeted at a specific group of pests (i.e. spring sprays for gypsy moth caterpillars or summer sprays for mite activity). Conventional pesticides, because they are manufactured, are mostly inexpensive and can be tailored to control a certain pest or group of pests. Control of pests is usually immediate, but they can persist in the environment for weeks to years depending on the material and it's chemical structure. These pesticides are regulated by the Environmental Protection Agency on the federal level and by the Department of Environmental Conservation on the state level, and are required to go through testing for a period of 5-10 years before they are approved and given a EPA registration number.
Organic horticulture is more precautionary. You try to prevent problems from occurring by maintaining the health of the plants. With very few exceptions, insects will attack plants that are under stress or weak for any number of reasons (improper planting, poor soil conditions, improper site location, etc.). The main weapon in the Organic horticulturalists arsenal is proper fertilization, a beneficial fungus called mycorrhizae and soil amendments to restore the proper balance of nutrients in the soil. Healthy trees and plants are less likely to attract damaging insects and more resistant to diseases. Biological or Natural materials are for the most part slower acting and less persistent in the environment, most of them only lasting for a short time before biodegrading. Because of this, more applications may be required, to control the same pests that conventional pesticides will with one treatment. Many of these materials are exempt from EPA testing and therefore carry no registration number.
No matter which pest control program you opt for, make sure that you have a certified applicator doing your treatments, this will assure you that you have a trained professional working with these materials. If you opt for an organic program for either the trees or lawn, you will need to switch over to organics for the other as well. Any chemical application can wipe out any progress that the natural materials are making. Be warned some companies are using materials listed on the exempt materials list, or the same pesticides they always used (with a material called Mask-it, which gives the mixture an orange or citrus smell), and call it an Organic treatment, you can tell the difference when they spray, if things are dropping out the trees immediately, then it was not an organic spray.
If you want more information, or have questions, you can contact me by E-mail at firstname.lastname@example.org or visit the website of the Lyceum school for organic horticulture (of which I am a graduate) or contact LIOHA (Long Island Organic Horticultural Alliance) at 516-541-4321.