Wind machines and frost protection in New Zealand

Abstract

Wind machines have been widely used as a frost protection method for the last 30 years, particularly in the Western U.S. Although there were some early attempts to investigate this method for New Zealand conditions it is only recently that the system has gained popularity. Under frost conditions the air temperature above an orchard may of ten be warmer than the air closer to the ground, and it is this ''inverted" temperature profile which allows a wind machine to work. The formation of this inversion profile is described and the way in which a wind machine modifies it to provide frost protection is discussed. A review of the performance of typical wind machines is given followed by a summary of the temperature profile measurements which have been made in the various fruit growing areas in New Zealand. It is concluded that, although wind machines probably have a place in frost protection in parts of New Zealand their use should be considered with care and a full appreciation of the risks involved.