The Pest Exclusion Program provides the first line of defense for California's agricultural industry and environment from the introduction of exotic insects, weeds and plant diseases that "hitchhike" in from other counties, states and countries. Incoming shipments of plants and produce arrive at various locations in the County including San Francisco International Airport and wholesale nurseries where they are inspected for harmful pest and diseases. Shipments of agricultural commodities destined to other states and countries are inspected and certified for compliance with quarantine requirements.