In fruit trees, yearly applications of a dormant or delayed-dormant treatment are the key to successful pest management. Many gardeners are familiar with the use of horticultural oils to control scales, mites, aphid eggs, or caterpillar eggs on fruit trees in the dormant season. Generally, trees are completely dormant from December to January. The delayed-dormant period begins in February as buds begin to swell, and continues until the beginning of the green tip bud development stage. If neither a dormant nor delayed-dormant treatment is properly applied, additional treatments may be required throughout the season.
Treatments should always be made before budswell and when trees are not water stressed to avoid injury to trees. A good time to apply them is right after a period of rain or foggy weather. Do not apply them during fog, rain, or during or prior to hot or freezing weather (over 90° F or under 32° F). On deciduous trees, oils should not be applied within 30 days before or after applications of sulfur or certain other fungicides to avoid damage to trees. Dormant-season applications are not appropriate on citrus or avocado because these trees do not enter a winter dormancy. Oils are not recommended for use during the dormant season on walnut trees.
