It’s natural to think of our fruit trees as not needing care in the cold winter months, when they are leafless and dormant. But in fact, dormant sprays applied throughout the winter can help you get a head start on disease and insect problems that could impact the health of your fruit trees year-round.
Gardeners often ask us for advice about controlling fruit tree pests during the summer months, when their trees are already loaded with ripe fruit. For gardeners who wish to treat these problems aggressively, 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, but 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 insect pests
If your trees suffered from insect damage last summer, horticultural oil is one solution that can be used in organic gardening. Many gardeners are familiar with neem oil, a plant-based oil that can be used to smother pests. Horticulture oil is a heavier mineral oil that is more effective in our wet winters.
Horticultural oil works by coating and suffocating any insects or insect eggs that might be overwintering on your trees. It breaks down quickly, which reduces its long-term environmental impact. Although all pesticides carry some risks and will kill any insects present, proper use of horticultural oil in the winter is thought to have minimal impact on pollinators and other beneficial insects.
The goal is to spray all of the favorite hiding spots for overwintering insects: leaf buds, in branch cracks and in junctions between branches. I know that may be easier said than done, especially on taller trees, so you might want to use a hose-sprayer, which can project the spray further. Of course, you should make sure to follow all directions on the label.
Dormant sprays for fungal disease
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.
To learn more about year-round care for all kinds of fruit trees and much more, stop by our all-day Prune-a-thon on February 4th, hosted in conjunction with Plant Amnesty. Don’t forget to RSVP on Facebook to get the latest updates. Check out our website for a full list of our early spring events.
About the author: Geoff has been working with customers in Sky Nursery’s tree and shrub department for ten years. He also volunteers with Seattle’s p-patch program.