Q: I had a big problem with aphids last summer, and the leaves on my peach tree were distorted. A neighbor says I should try a dormant spray, but I don’t like using chemicals. What should I do? Fatima Carmo, San Luis Obispo
A: We gardeners have become increasingly wary about the use of pesticides, preferring more sustainable gardening practices. There are times, however, when a dormant spray can be an important part of a preventive program and minimally disruptive to the environment. Good pruning practices and sanitation combined with well-timed dormant sprays can help control certain insect and disease pests, with less impact to beneficial insects.
The term “dormant spray” is generic, and refers to any spray applied to deciduous trees and shrubs during fall, winter and early spring when leaves are absent. Spraying can be done from the beginning of the dormant season — around November — until just before the buds begin to swell. Once budding has begun, sprays may damage fruit or flowers.
Dormant spraying should be part of a thorough deep cleaning program. Just as it is easier to vacuum a room thoroughly when the furniture has been moved, more can be accomplished using less chemical when there are no leaves to block the spray. Prune to remove dead, diseased, or broken branches and to open the canopy to sun and air circulation. Remove mummified fruit from the trees, and diseased fruit, leaves and flowers from surrounding area.
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In the backyard garden it may not be necessary to apply dormant sprays every year if pest infestations have been kept to a minimum during the growing season. A possible exception would be peach and nectarine trees that are very susceptible to a fungal disease that causes leaf curl and that cannot be treated after budding has occurred.
There are many different pesticides used as dormant sprays. The insect or disease you want to control will determine which product will be most effective. The correct pesticide can be effective against insect pests such as aphids and mites, and certain fungal diseases. As always, careful attention must be paid to product labels, and the Master Gardeners are available to answer specific questions. Additional information and suggestions for dormant pest management practices for specific deciduous fruit trees can be found in the University of California publication “Winter Pest Management in Backyard Deciduous Fruit Trees” available on-line at http://ucanr.org/freepubs/docs/8368.pdf.