Dormant Sprays for Fruit Trees: prevent pest problems now

Summer fruit may not be the first thing on our minds in the winter, but dormant sprays are key to managing disease and insect problems.

Gardeners often ask us for advice about controlling fruit tree pests during the summer months, when their trees are already loaded with ripe fruit. We suggest a treatment plan that starts in the winter months, long before leaves and flowers have emerged.

The first step in an effective treatment plan is getting an accurate diagnosis. You need to find out the source of the problem so you can target it specifically. Some fruit tree problems can be solved simply by changing your watering schedule or other environmental conditions. Others might be best solved with a dormant spray.

If you can think back to insect or disease problems you encountered last summer, you can preempt them now with an appropriate dormant spray. And if you run into trouble this coming summer, we’ll be happy to help you get an accurate diagnosis here at Sky.

Dormant sprays for fungal diseases

Fungal diseases call for a different kind of dormant spray. Common fungal diseases on fruit trees for this region include powdery mildew, downy mildew, peach leaf curl, apple scab, and leaf spot. Copper in different forms can jump-start the control of overwintering fungus spores and stop these diseases before they start.

Copper ammonia, such as Liquid-CopTM, is probably the most effective disease control, but gardeners looking for a more organic solution might consider using a copper soap spray instead. As with horticulture oil, try to cover as much of the branch surface as possible.

Words to the wise

Timing can be tricky when applying dormant sprays. The Washington State University Extension Service lists optimal conditions as daytime temperatures between 45 and 55 degrees, and suggests that you finish spraying by noon. Of course, you'll also need to wait for dry weather, since rain will wash sprays away.

If we do have a rare sunny day, it’s best to spray in the morning to allow the spray to dry. Otherwise, the combination of afternoon sun and dormant spray can burn the leaves.

Keep in mind that copper sprays and horticulture oil should not be mixed together, and most manufacturers recommend allowing one spray to dry before applying the other. The interval between spray applications will be determined by the disease you are treating and the manufacture's instructions.

Dormant spraying throughout the winter and pruning in the late winter months are important parts of the year-round treatment plan for your fruit trees. Staying on top of pest and disease problems in the winter can be a challenge, but it will pay off in a bountiful summer harvest.

Post author, Geoff, has been working with customers in Sky Nursery's tree and shrub department since 2007. He also volunteers with Seattle’s p-patch program.