Do I Need to Spray My Apple & Pear Trees in the Winter?

Safety

• One reason to spray apple and pear trees in winter is because dormant-season sprays are very effective and very safe. They are generally natural substances, including newer paraffin-based horticultural oils, so there is no need to worry about toxic residues in trees, soil, air or water. Other common ingredients are lime, sulfur, copper and various insecticidal soaps made from potassium salts.

Timing

• The success of dormant spraying is in its timing. The goal is to eliminate pests and disease organisms while they are dormant or inactive and easier to target. The best time to spray depends on the product, climate conditions and the life cycles of pests or diseases. Check with a county agricultural extension or reliable nurseries for accurate local information. In most parts of California and the West Coast, for example, dormant spraying is done from November through March.

Sprays

• Dormant oil sprays work by suffocating or drying out the eggs and larvae of overwintering aphids, scales, spider mites and other insects -- including the apple maggot fly, responsible for wormy apples. Usually comprised of very fine horticultural oils, dormant oil sprays should be applied only when temperatures will be increasing. They can damage tree bark when applied at near-freezing temperatures. Lime sulfur sprays help knock out or at least slow bacterial and fungal diseases, including anthracnose, fire blight, peach leaf curl and scab. Copper sprays help control canker.

Strategy

• For apple trees, McShane’s Nursery in Monterey, California, suggests spraying copper before fall rain begins, dormant oil once or twice from January into March, lime sulfur just before buds open and wettable sulfur right after petals fall. The copper protocol is the same for pears. But pears need lime sulfur spray in the fall, winter and again just before buds open. Then apply dormant oil spray just before buds open and, after petal fall, wettable sulfur. McShane’s overall dormant spray strategy is to apply at least two different dormant sprays before pruning, one after pruning -- preferably copper, to protect open wounds from disease -- and then seal the tree with dormant oil to “suffocate the bad guys as well as seal out other unwanted visitors.” Allow at least two weeks between copper applications and any sulfur sprays.