Agricultural and Forest Meteorology, 60 (1992) 181 - 191 181 Elsevier Science Publishers B.V., Amsterdam Flower orientation influences ovary temperature during frost in peach Shaoli Lu, Mark Rieger and Michael J. Duemmel Department of Horticulture, University of Georgia, Athens, GA 30602, USA (Received 24 February 1992; accepted 3 March 1992) ABSTRACT Lu, S., Rieger, M. and Duemmel, M.J., 1992. Flower orientation influences ovary temperature during frost in peach. Agric. For. Meteorol., 60: 181-191. Ovary temperatures of upward- and downward-facing flowers of "Junegold' peach (Prunus persica (L.) Batsch) were measured on five nights in March 1991 to determine whether differential survival of ovaries following frost was related to flower orientation. Flowering twigs were removed from mature trees and positioned horizontally approximately 1.5 m above ground level prior to occurrence of low temperatures (0-5°C). Thermocouples were inserted through the hypanthium to contact ovaries of upward- and down- ward-facing flowers, and temperature and meteorological data were logged every 5 min. Under clear, calm conditions, temperature of upward-facing flowers averaged 0.33°C lower than that of downward-facing flowers during the coldest period of the night, with maximal differences of 0.77°C. Under cloudy, calm conditions, temperature differences between upward- and downward-facing flowers were less frequently observed and lower in magnitude (0.08q).l 5°C). Under windy conditions ( > 2.5 m s-t ), no temperature difference between upward- and downward-facing flowers occurred despite strongly negative net radiation. Differences in radiant heat exchange when forced convection was minimized are proposed to have caused the differential temperatures between flowers of different orientation. Based on known values of ovary cold tolerance, it is concluded that differences in survival of up to 38% could occur due to flower orientation when air temperature reaches critical values. INTRODUCTION Spring frost damage is a serious limitation to production of peaches and other Prunus species. For example, severe peach crop losses occur about every other year in the eastern USA. Years of observations indicate that certain cultivars produce higher yields following frost than others, although the mechanisms of frost tolerance remain uncertain. Several mechanisms are possible, including delay of bloom date (avoidance of frost altogether), high flower bud numbers/tree which permit production of commercial crops Correspondence to: M. Reiger, Department of Horticulture, University of Georgia, Athens, GA 30602, USA. 0168-1923/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.