Answer: Like all fruits and vegetables that are grown commercially in the U.S., peaches are subject to numerous pests (insects and diseases) that must be controlled so that wholesome and unblemished fruits can be successfully produced for sale in the market. Whether peaches are commercially grown using organic or conventional methods, pesticide use is normal and necessary.
Without the use of pesticides, the natural insect and diseases present in the environment would cause direct damage to the fruit and make it unmarketable. Further, some diseases and pests damage the tree as well and can cause loss of tree productivity and premature tree death. Commercial fruit growers are concerned about the safety of their fruit for the consumers who buy them. They are trained on the appropriate, safe and legal use of approved products to protect peaches.
They are licensed by the state and must keep good application records which may be inspected. In most commercial operations that are supplying boxed fruit to the chain stores, the fruit are brushed and washed before shipping. However, there may still be some pesticide residues on the fruit. These pesticides are in extremely low and legally permissible concentrations – much below any level that could impact human health. As with any fresh fruit from the market, it is always best to wash it with clean tap water before eating. The "Dirty Dozen" list was established by a private environmental advocacy group,, the Environmental Working Group (EWG), and are not a government or university organization.
Recently, Drs. Carl Winter and Josh Katz of the Department of Food Science and Technology at the University of California-Davis published a peer-reviewed, scientific article in the prestigious Journal of Toxicology (2011) entitled "Dietary exposure to pesticide residues from commodities alleged to contain the highest contamination levels" (PDF). In their study, which included peaches and nectarines, they made three noteworthy conclusions: "(1) exposures to the most commonly detected pesticides on the twelve commodities pose negligible risks to consumers, (2) substitution of organic forms of the twelve commodities for conventional forms does not result in any appreciable reduction of consumer risks, and (3) the methods used by the environmental advocacy group to rank commodities with respect to (potential) pesticide risks lacks scientific credibility." To read the full article, please see the following link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3135239/.
For more information on the health benefits of peach, please see my FAQ entitled "What is the nutrient value of a peach?".
For more information about pesticides, you can visit the Pesticide Information Program at Clemson University website at: http://www.clemson.edu/extension/pest_ed/