Changes affecting fruit set start in preceding summer. Sufficient water during preceding summer assists the change from vegetative buds into flower buds. Stress from water shortage, pests, diseases and nutrient deficiency can severely affect fruit development and yield. Flowering usually occurs in September and October, depending on variety and conditions. July and August are critical for ensuring tree is in peak condition. Dry-land trees can have as many as 52% sterile flowers, compared to suitably irrigated trees with 7-8%. Trees must be exposed to winter chill to bear fruit. Average temperature for July should be 12 degrees Celsius or less for adequate chilling. Hot dry winds during flowering will tend to increase flower drop and reduce fruit set. Olive trees in suitable environments produce abundant pollen. Correct irrigation and windbreaks reduce the detrimental effects of heat and wind on fruit set.