International Symposium on Food Production in the Face of Global Environmental Deterioration　(2004.9.7-11) 

Recently, unfavorable fluctuations of weather have been intensified. For many fruit growers, this recent situation increased the needs of protected cultivation, which allows the growers to control the onset of flowering as well as the time of harvest. 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 with a reflective film (DuPont, Tyvek) was employed independently or together with an evaporative cooling device (large-sized ultrasonic humidifier).

Tyvek film is characterized with a high albedo (reflectivity of short- and long-wave radiations). It was reported in the preceding report (Honjo et al., 1999) that the film covering above the top of the trees (floating cover) prevented temperatures from rising during daytime and kept canopy temperature warmer than in the open field at night. The diurnal range of temperature under the floating cover 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 effective in sunny and calm days. For example, temperature decrease was estimated roughly 5-6°C lower than the air temperature in outdoors during the sunny daytime in November.