Temperature effects on ethephon thinning of apples

SummaryThe effect of temperature on ethephon thinning was studied using regularly flowering mini-trees in 22-1 tubs, half of each tree being sprayed with 400 ppm ethephon at petal-fall. The trees were placed in rooms at 4°, 8°, 12°, 16°, 20° and 24°C for 4 h prior to and 24 h after spraying. The control treatments and the ethephon treatments at 4° and 8°C had effectively the same fruit set. Thinning increased with temperature from 12°C to 24°C, the relationship being a significant linear regression. The importance of temperature in predicting ethephon thinning through modelling is discussed.