Zebra mussel: Can cause severe fouling of municipal drinking water, electric power generation, and industrial water systems; they are also harmful to aquatic ecosystems, boating and navigation, agricultural irrigation equipment, aquacultural equipment, and recreation beach use. This mussel was first discovered in the Great Lakes of the U.S. in 1988, and is believed to have arrived in North America in the ballast water of a cargo vessel. Since the first discovery of this exotic species, they have spread rapidly through North American surface waters, particularly throughout the Great Lakes and Mississippi River basins and their navigable tributaries.

Zero certification: Under former programs, producers who chose not to plant any acres to a program crop in any particular year could “zero certify” such acreage and protect the base for historical purposes. The farm must have been enrolled in the program in order to be eligible to “zero certify.”

Zero discharge permits: As authorized by the Clean Water Act of 1972, permits for feedlots requiring that the wastewater facilities be designed, constructed, and operated to keep wastewater from overflowing, except during the largest 24-hour rainfall that occurs on the average of once every 25 years (a 25-year, 24-hour storm event).

Zero till(age): Tillage in which disks push aside residue of the previous crop just prior to planting. There is no seedbed preparation.

Zero tolerance rule (policy): (1) A Food Safety and Inspection Service policy on visible fecal contamination of poultry, specifying that poultry carcasses contaminated with feces are not allowed to enter chilling tanks where contamination could spread to other carcasses. (2) A part of the FSIS Pathogen Reduction Program in which carcasses and carcass parts are closely scrutinized for any form of contamination, and when found, the contamination must be totally eliminated and discarded before that carcass or carcass part is able to be further processed.

Zone(s): See Empowerment Zone and Enterprise Community program (EZ/EC).

Zoning: See Agricultural zoning.

Zoonotic disease(s): Diseases that, under natural conditions, are communicable from animals to humans. Included among these are brucellosis (undulant fever), salmonellosis (salmonella poisoning), leptospirosis (Weil’s disease), anthrax (woolsorter’s disease), and tetanus (tetanus or lockjaw). Also Zoonoses.