Peaches, almonds and many other kinds of deciduous fruit trees are vulnerable to diseases and insects that can affect both their health and the quality of the crop. These problems can be difficult to manage during the warm season, but applying oils and other treatment during the trees' dormant period can keep trees healthy. Because these treatments can damage trees during the growing season, it's extremely important to limit spray application to the right season and apply only during favorable weather.
Dormant Oils and Sprays
Dormant and delayed-dormant sprays are pesticides applied before the tree exits the winter dormant period. They help destroy insect eggs, over-wintering adults and hatching larvae. They can also kill fungal infestations that could spread in warmer weather. Dormant sprays are best applied shortly after pruning, since there are few to no leaves to block an even application. These treatments are especially effective against scale insects, mites, aphids, leaf curl and shot hole. They do not affect Oriental fruit moths and some types of spider mites.
Dormant Vs. Delayed-Dormant
Sprays meant for use during the dormant season can be divided into two groups: dormant and delayed-dormant. Dormant sprays must be used before the trees experience any spring growth. In California, this is usually between December and January. Delayed-dormant sprays are designed for use just after the buds begin to swell, but before the trees leaf out or flower. This usually occurs in late February to early March. Dormant oils must never be used when the tree is in flower, since they can be deadly to pollinators.
Wait until good weather before you apply dormant sprays. Ideally, the temperature should be between 40 and 70 degrees Fahrenheit. Do not apply a dormant spray during rain or fog or when the weather is expected to be extremely hot or cold within a few days. Application shortly after a period of foggy or rainy weather can actually make the sprays work better, however.
Dormant spray application is unsuitable for citrus fruit or avocado, since these trees do not go into a dormant state and can be harmed by the spray. Walnut trees do enter a dormant state and can undergo treatment with some types of dormant spray, but may suffer from damage if treated with dormant oils. No tree should receive dormant season treatment within 30 days of applying sulfur fungicide or during periods of water stress.
- University of California: Winter Pest Management in Backyard Deciduous Fruit Trees
- University of California Integrated Pest Management: Applying Dormant or Delayed-Dormant Treatments
- Utah County Online Extension Service: Dormant and Pre-bloom Sprays
- Texas A&M University: Fruit Trees
- Texas A&M University: Now's the Time for Dormant Oils
- Texas A&M University: Dormant Oil
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