Dormancy and Flowering Control for Japanese Pear by Micrometeorological Modification

Abstract

This study was conducted to improve the method of controlling the flowering date of Japanese pear trees without using any chemicals, heating equipment or extensive labor. The covering method using a reflective film (DuPont, Tyvek) was employed independently or together with an evaporative cooling device (large-sized ultrasonic humidifier). The diurnal range of temperature covering above the top of the trees became smaller than that in the open field. Thus, it was expected in terms of its chilling requirement that the prolonged period of low temperatures was effective in breaking the endodormancy. But, when the film was laid on the ground, the diurnal range in the tree canopy extended more than that in the open field as a consequence of the rise in daytime temperature due to the high reflectance of solar radiation. Considerable drops in air and bud temperature were recorded when used with the evaporative cooling device. Evaporative cooling worked more effectively in sunny and calm days. For example, temperature decrease was estimated roughly 5°C lower than the air temperature outdoors during sunny daytimes in November. Covering over the trees before endodormancy break forced flowering, but covering during ecodormancy delayed flowering. In contrast, mulching under the trees during ecodormancy forced sprouting and flowering. Such a method of controlling (forcing and/or delaying) the flowering of Japanese pear was more effective with using the evaporative cooling device.