| Abstract: | Whether or not fruit buds in orchards can be protected from freezing by the use of fans, when no temperature inversion exists, depends upon the degree of bud radiant cooling at such times. Nighttime bud cooling in apple and peach orchards was estimated by comparing the temperature of buds and the adjacent air. The extent of radiant cooling was usually less than 0.6°C below ambient. Even this modest degree of radiant bud cooling appeared to require conditions with less than 60% cloud cover and wind speed less than 1 to 1.5 m s?1 at a height of 2 m. However, such conditions were also accompanied by inversions. The protective potential of fans in the absence of an inversion (postulated on the basis of bud radiant cooling) is therefore disclaimed on two accounts: (1) that the bud/air temperature difference is quite small and would only rarely span the bud critical temperature, and (2) that bud cooling would probably not occur during conditions which prevent the presence of an inversion. |
