Spraying Delayed-Dormant Oil on Backyard Fruit Trees With a 2-Gallon Pump Sprayer: Bud-Swell Timing, 40°F Minimum, and Full Bark Coverage

Gardener misting horticultural oil onto a bare apple tree with swelling buds

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Aphid eggs, scale nymphs, and mites spend the winter tucked into bark and buds. One well-timed oil spray in late winter smothers many of them before they ever reach the leaves.

When should you spray dormant oil on fruit trees?

Spray around bud swell, after the buds start to swell but before bloom, on a calm, dry day near 50 to 70°F. Temperatures should stay above freezing for at least 24 hours afterward. Wet every crack in the bark and every bud, and follow the oil label's rate.

Utah State University's delayed-dormant spray advisory says the best timing is after trees break dormancy but before bloom, when overwintering insects become active. It lists the last safe stage for apple as half-inch green, with green tip the ideal.

University of California IPM's dormant treatment page says not to spray during fog or rain or before weather over 90°F or under 32°F. It says not to apply oil within 30 days of sulfur or certain other fungicides on deciduous trees.

Delayed-Dormant Oil Numbers

Item Figure Source
Apple, last safe stage Half-inch green USU
Cherry, last safe stage White bud USU
Pear and plum, last safe stage Green cluster USU
Peach, last safe stage Pink showing, before first bloom USU
Ideal spray temperature 50 to 70°F USU
Above freezing after spraying At least 24 hours USU
No rain forecast Within 24 hours USU
Gap from sulfur sprays 30 days before or after UC IPM

Reading the Two Sources

USU recommends waiting for bud swell, because spraying too early misses insects that are not yet active. UC IPM, writing for California, says treatments should go on before budswell and when trees are not water stressed.

Check your own state extension's advice for your climate. Either way, the label decides the rate and the crops it can go on.

Mixing and Coverage

USU lists a backyard rate of 2 percent, about 5 tablespoons of oil per gallon of water. Use the rate on your product label if it differs.

Shake or swirl the sprayer often, since oil separates from water. Work around each tree so the spray reaches both sides of every limb.

Materials and Tools

  • 2-gallon pump sprayer
  • Horticultural oil labeled for dormant or delayed-dormant use on fruit trees
  • Measuring spoons kept only for garden chemicals
  • Safety glasses, chemical-resistant gloves, and long sleeves
  • A step stool for the upper limbs of small trees

Spraying Steps

  1. Check bud stage. Compare buds to the last safe stage for each tree.
  2. Check the forecast. Look for calm, dry weather above freezing for 24 hours.
  3. Read the label. Note the rate, the crops listed, and the required PPE.
  4. Put on PPE. Wear glasses, gloves, and long sleeves.
  5. Mix in the sprayer. Add water first, then oil, then water to the mark.
  6. Pump and shake. Build pressure and agitate the tank.
  7. Spray the trunk up. Wet the bark, crotches, and branch tips.
  8. Agitate as you go. Shake the tank every minute or two.
  9. Clean the sprayer. Rinse it out the same day.

Mistakes and Hazards

  • Spraying after bloom has started
  • Spraying with a freeze or heat wave coming
  • Mixing oil near sulfur sprays
  • Letting oil separate in the tank
  • Spraying on a windy day, so drift misses the tree

Prune first so oil reaches every limb, as in clearing water sprouts and root suckers. Apples and pears with fire blight also need cutting out fire blight cankers during dormancy.

Young fruit trees also need trunk guards against rodents. See the hardware cloth mesh size and gauge guide.

FAQ

Do I need to spray every year?

USU says to apply the spray if your trees have had the pests it targets. If not, you can skip it.

Can I spray citrus or walnuts?

UC IPM says dormant-season sprays are not appropriate on citrus or avocado, and oils are not recommended during the dormant season on walnut trees.

What does the oil actually do?

USU says the oil works by smothering eggs and other overwintering insect stages.

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