Studies on the thermal conditions of grapes. VI

Effects of day and night temperatures on yield and quality of Delaware grapes

Abstract

1. The effects of day and night temperatures on the berry growth, yield and quality of Delaware grapes were observed in each of the growth stages, berry enlargement and maturity. As a result, when expressed on the basis of berry temperature itself, the suitable day and night temperatures were approximately the same, being always about 22°C. However, for the promotion of berry maturity, a higher temperature than 22°C was favorable, although never allowed to exceed 30°C.
2. In mid-summer, the air temperature at daytime readily reached more than 30°C, and berries had a temperature higher than the air by 5° to 6°C, receiving intensive sunlight. Therefore, the optimum berry temperature for the berry growth and quality was usually found at night. Judged from this fact, a difference of temperature between day and night or a low night temperature seems to be necessary in the stages of berry enlargement and maturity in increasing yield and berry quality of Delaware grapes.