In a world of humanmade chemicals, pesticides are second only to fertilizer in the amount applied and the extent of use. They are effective tools for protecting crops, fighting disease-causing insects and dealing with nuisance animals such as rodents, fleas and ticks. But herbicides, insecticides and their kin can harm the environment and are dangerous to workers if improperly used.
In 2007, the last year for which the Environmental Protection Agency produced global figures on pesticide use, the United States accounted for 20 percent of the worldwide application that topped 2.4 billion kilograms.