Take advantage of brief patches of nice weather to dormant spray. Winter spraying, while trees and shrubs are not actively growing, can prevent or reduce many significant diseases.
Copper sprays are very useful for dormant applications. They provide suppression or control of both fungal and bacterial diseases. Spray fruit trees and berries to reduce scab, mildew, leaf and cane spots, and bacterial blights. Dormant sprays can also help subdue rose black spot, lilac bacterial blight, and dogwood anthracnose on ornamentals.
Timing of Spray Applications
For successful dormant sprays, keep in mind a few guidelines:
Plants should be dry when spray is applied. Even light sprinkles or heavy dew can over-dilute the spray, reducing effectiveness. Wait until branches are no more than moist, not dripping.
Do not spray when the air temperature is below freezing, or is expected to drop below freezing before spray dries. Freezing weather on wet spray can damage buds.
Spray will usually take 4 to 6 hours to dry. During that period, even a light shower will wash it away, requiring a new application. Even after the drying period, heavy rains impact spray effectiveness – re-apply a dormant spray if it gets washed away in the first 2 to 3 days after application.