If your shrubs and trees suffered during spring and summer—due to pests, diseases like fungal infections, or burrowing insects that damaged fruit trees and other garden plants—consider using dormant winter spray treatments.

‘Dormant spray’ broadly refers to applications like horticultural oil, which smothers overwintering insects such as aphids, mites, and scale, along with their eggs. Another type uses synthetic fungicides or copper to treat fruit and flowering trees and shrubs, giving your plants a healthy start in spring. Sometimes, liquid lime-sulfur is applied to smaller fruit plants, such as blueberries or blackberries, to control fungi and bacteria.

Dormant sprays should be applied after the growing season, but before temperatures drop below 40°F. While a pre-winter treatment can suppress spring pests, it may not provide complete control. Regular treatments throughout the year may be necessary for optimal plant health.

Common dormant sprays include:

• Fixed copper fungicides containing elemental copper, such as tribasic copper sulfate, copper oxychloride sulfate, or cupric hydroxide
• Neem oil is derived from the seeds of the neem tree (Azadirachta indica)
• Lime-sulfur, a mixture of hydrated lime (calcium hydroxide) and sulfur
• A crucial but often overlooked step in keeping trees and shrubs healthy is good housekeeping—regardless of whether you use dormant sprays. Remove fallen leaves from around your plants to prevent pests from laying eggs or overwintering, as they can also spread disease to other plants and undermine your disease control efforts.