How and When to Spray Dormant Oil on Fruit Trees

Winter and early spring are the best seasons to combat pests and diseases. They hibernate on fruit trees and are susceptible to organic oil treatments. Tackle them now and you’ll have less damage control to do later on! Learn how and when to spray fruit trees with this easy-to-follow guide from backyard gardener Jerad Bryant.

Close-up of a woman's hand holding an orange sprayer, applying dormant oil to a plum fruit tree.

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Though pesticides and fungicides seem harmful to the environment, there are organic treatment solutions that have a low impact on the surrounding ecosystem. Spraying horticultural oil on fruit trees during winter is one way to safeguard your future harvest without harming pollinators, predatory bugs, and wildlife.

Most pollinators lie dormant as pupae or overwintering adults, while predatory bugs are absent because not much prey is around. Though these beneficial creatures aren’t on your trees, overwintering pests and pathogens are! They hide under the bark or in fissures on branches, waiting for warmer temperatures to emerge.

When you spray your trees in winter, you avoid harming beneficial creatures while targeting pests and diseases that persist through the cold months. The oil may fall to the soil, but some organic amendments ensure all the residue decomposes without harming soil life.

Let’s first see the best time to spray solutions and which types to use before applying them. Grab a coat, a beanie, and some gloves, and get ready to protect your fruit!

When to Spray Dormant Oil

A gardener wearing a white mask and glasses sprays bare trees in a snow-covered garden.
Spray in winter for pest control before leaves appear.

December through January is the best time to spray dormant oils in North America. Most deciduous species are hibernating; they have buds on their branches but no leaves. You want to time your spraying regimen so that it’s through by the time leaves emerge from the buds.

Some species break buds in late February, though most open up in March or April. Complete your spraying by February to allow plenty of time for the oil to work without harming pollinators, predatory insects, or the trees themselves! A good rule of thumb is to spray dormant oils at the same time that you winter prune. 

The other consideration is frost; freezing temperatures disrupt the oils’ effectiveness. Spray them 48 hours before or after a hard freeze for optimal results. You may have to reapply the oils after hard freezes if pests or diseases persist. 

You shouldn’t apply oils every year, as they’re only effective in treating pests and diseases. They’re unnecessary if none are present! Watch your trees during the growing season to see if they need applications this year. Watch for fungal, bacterial, and pest damage on branches, leaves, flowers, and bark.

Three main types of sprays work well for organic control in home gardens. Horticultural oil targets pests, while sulfur and copper sprays target fungal and bacterial infections. Using all three in rotation ensures no overwintering pests, bacteria, or fungi can reinfect the tree when spring arrives. 

6 Steps for Spraying Dormant Oil

These six easy steps take you from start to finish so you can spray your trees and scurry off to the warmth indoors. You may need to repeat this process several times to ensure each spray covers the tree. Start in December so you have plenty of time to diagnose mishaps. 

Step 1: Prune Unruly Branches

Close-up of a gardener's hands trimming bare tree branches with red pruning shears.
Remove dead wood to help treatments work more effectively.

This guide is for spraying oils, so why should you prune your fruit trees? For starters, pruning clears crisscrossing branches so the treatment solutions stick to the trees better. It also exposes pests and fungal bodies that hide in crevices. Open them to the elements and you’ll have a good chance at eradicating them. After pruning, an oily application protects the cut wounds so they heal well. 

Prune your fruiting trees by locating dead or diseased branches first. Use loppers or pruners to lop them off a little above the branch collar so the wound you leave behind heals without issue. The branch collar is where the side branch connects to the main one. It has a slight bulge that’s wider than the branch itself. Prune so there’s a little stub above this collar—it’ll heal over and blend in with the trunk as the tree grows older.

After pruning dead and diseased wood, locate any crisscrossing branches that grow against the direction of all the others. Take care not to remove more than a third of the tree to avoid shocking it—shocked specimens sprout lots of leafy shoots at the expense of fruit when they break dormancy.

Step 2: Mix Your Solution

A gardener pours an oil-based gardening solution into a pressure sprayer in a sunny garden.
Separate treatments and apply weeks apart for best results.

Some solutions require mixing while others come pre-mixed. Pre-mixed sprays are easier to use, though they’re more expensive than ones you mix. Choose whichever option works best for you and your garden. 

While you may want to mix all the solutions into one for spraying, it’s best not to! Use separate solutions for each treatment, and apply them several weeks after each other. Always follow the instructions on the package’s label for proper mixing and dosing rates. You should aim for two or three applications per winter to avoid overwhelming the site with oil. 

Horticultural, or superior, oil works well for controlling scale, aphids, mites, and peach tree borer. The oil smothers insects and eggs so they can’t emerge in spring. Copper solutions work well for controlling bacterial cankers, fire blight, and short-hole fungus. Sulfur solutions combat various fungal diseases like apple scab and peach leaf curl. 

Whichever application works best depends on your trees and the conditions they’re suffering from. Though other options are available, these organic solutions offer proper treatment with little impact on your local ecosystem. Keep your garden and its lovely critters safe by avoiding toxic synthetic pesticides, fungicides, or bactericides that harm more than they fix. 

Step 3: Prepare Sprayer

Hands in yellow gloves hold an orange sprayer, spraying bare tree branches in a sunny garden.
Shake the sprayer well before using it for even application.

You’ll need a proper sprayer if you’re mixing your solutions! Handheld ones are simple to use though they may take a long time to cover a mature tree. Pressure or backpack sprayers work quickly, allowing you to cover old specimens easily. Both require you to pump a pressurized tank—when you press on the trigger, the sprayer uses the pressure to release a steady stream.

After filling the sprayer with solution, shake it up so you distribute it evenly. Pressurize the tank, then get ready to spray your orchard. Remember, frost, rain, ice, and snow interfere with the applications, preventing them from working properly. Distribute them on clear days when no rain or snow is forecast. 

Step 4: Spray Fruit Trees

A man in a yellow overall, mask and glasses sprays bare trees in a sunny winter garden.
Apply copper and sulfur solutions at recommended intervals.

Now it’s finally time to spray the orchard! Put on a mask for protection from the fumes, then grab your sprayer and drench the trunks, branches, and dormant buds. Ensure every specimen receives the application on all parts, leaving no bare patches. Further instructions on the spray package’s label will advise you on proper application rates. 

OSU’s extension service offers an easy treatment plan that’s hard to forget. Start with a copper solution on Thanksgiving, a sulfur one in early January, and horticultural oil two weeks later. Then, apply one more copper solution in mid to late February. This regimen avoids damage to your orchard, as mixed oils can harm sensitive bark. 

Step 5: Clear Debris

A gardener in blue gloves holds a shovel full of dry branches and leaves collected in the garden.
Leave leaf litter unless pests or diseases are present.

Once the spraying is over, some extra steps guarantee further protection against invaders. Some may overwinter in fallen debris, especially in fall leaves from diseased specimens. Clear the debris and dispose of it far from the site by composting or burying it a foot or two underground. Remove fallen twigs or branches that may have overwintering pathogens on them. 

Though this is necessary for diseased specimens, it may be harmful if there are no diseases or pests present. Many beneficial critters like fireflies, bees, and ladybugs overwinter in leaf litter. Only clear debris from the site if you see symptoms of infection or infestation, or if you’re growing a tree that generally has pests and contracts diseases. Otherwise, leave those leaves!

Step 6: Add Compost

Close-up of a shovel full of compost next to a young fruit tree in a garden with a green lawn.
Apply compost to nurture roots and protect them from pathogens.

Without debris, the bare soil exposes sensitive tree roots. Add compost to the site to protect, bolster, and boost your orchard’s performance. Compost inoculates the soil with beneficial fungi, bacteria, and archaea that keep bad microbes away. Larger creatures like worms move through it, creating channels for air and water to travel. 

After spraying dormant oil on your fruit trees, add a layer of compost two to three inches thick on top of the soil, leaving some room around the trunk to avoid rot. Water it so it stays moist and sticks to the ground, then wait for it to work its magic. Compost contains many nutrients that feed the roots in spring, creating a more resilient specimen that resists pathogens and pests. 

Without compost, leaf mold works well as an organic mulch substitute. It contains lots of carbon from fall leaves and is perfect for boosting your home orchard’s health. Add a layer two to three inches thick after clearing debris, and reapply every fall or spring. 

Frequently Asked Questions

Will rain wash off dormant oil?

Yes, rain will wash off dormant oil. Frost, snow, and ice also interfere with it, causing low success rates.

How often is best to spray?

You want to apply two to three applications during the winter months, depending on how many solutions you’re applying. Follow a regimen like the one described in step four.

When should dormant oil be applied?

Apply it in winter, when deciduous trees are dormant. If there are leaves on the tree it’s too early, and if the buds are opening it’s too late.

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