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Ultralow volume When used to describe pesticide application to plants, this term refers to the application of a very low volume of liquid pesticide formulation per unit area. When less than 5 gallons is used per acre (47 l/ha), the application is referred to as low volume; below one gallon per acre (9.5 l/ha), it is referred to as ultralow volume. (Nelson, 2003)

Uneven-span greenhouse A greenhouse with one roof slope longer than the other, generally an adaptation to a hillside. (Nelson, 2003)

Unit heater A forced-air heater. Unit heaters are usually mounted overhead in a greenhouse. They may contain a firebox or receive heat in the form of steam or hot water from a boiler elsewhere. (Nelson, 2003)