Monday, January 29, 2018

Applying Dormant Oil

We are having a warm spell.  Perfect time to get work done in the orchard and yard and enjoy the sunshine.  Right now you should be focusing on two things:

1.   Pruning peaches, apricots, and sweet cherry (if needed). It is OK to prune them up to pre-bloom.  You have a little more time with apples and pears but they should be pruned also.
2.  Apply horticultural oil and/or copper now, or in the next few weeks to all woody plants including perennials, ornamentals, berries, shade and fruit trees.
Horticulture oil is the proper term for the oil.  It can be used as a dormant oil or a light summer oil.

Despite the fact that we call it “dormant oil”, the timing of a horticultural oil spray is not when trees are still dormant.  A better term would be a “delayed-dormant” because the oil should be applied after bud swell which results from the sap beginning to flow.  This just happens to coincide with the increased activity of the overwintering insect, such as aphid eggs, scale nymphs, and peach twig borer larvae.  The oil smoothers insect eggs and larvae.  It is effective against aphids leafhopper nymphs, mealybugs, mites, plant bug nymphs, psyllids, sawfly larvae, scale, thrips and the early stages of caterpillars.
 A young apple tree pruned and ready to spray.  This is a heritage variety:  Ashamed Kernel a cooking apple.

In my zone, some trees like plum and apricot have already bloomed but it is still ok to apply the oil to peaches, cherries, apples, and pears. 

When to Spray

There are a few factors  to consider when determining the right time to spray: the bud stages of your fruit trees and temperature.
Peach blossoms at pink tip stage.

Bud Stages

The window for application extends from bud swell to when leaves just start emerging. The last point at which you can safely apply oil is:
  • apple: half-inch green (ideally, application is made at green tip stage)
  • pear: cluster bud
  • apricot:  up to first bloom
  • cherry: white bud
  • peach/nectarine: pre-bloom (when the pink shows through the bud)
(Information from USU Extension)

Here is a link to pictures of the bud stages to help you identify what stage your buds are in.  It also includes information on critical temperatures for frost damage.

Plum tree blossoms already opening do not spray when flowers are blooming.


When using horticulture oil, the air temperature is important.  Horticultural oil should on be applied when the night time temperature will not be dropping below 45 degrees F.  This gives a 24 hours period of appropriate temperatures.

After pruning these blackberries,
I will spray them with dormant oil.

Types of Horticulture Oil

The active ingredient in organic dormant spray or horticulture oil is cotton seed oil. When the oil is dry it does not harm beneficial insects. 

 Non organic sprays may be petroluem based. 

This is a nanking cherry I pruned as a small tree.
Beautiful in full bloom.

Summary of Horticultural Oil Application

  • Trees need to be in the proper bud stages before spraying.  This is when the sap begins to flow and buds swell.

  • The temperature will stay above 45F for 24 hours

  •  Horticulture oil can be used as a light summer spray directly on foliage or as a dormant oil on the bark of ornamentals, berries, shade, and fruit trees.  The application rate is different for each use so follow manufactures instructions.

  • When spraying apple trees, if fire blight is a problem you can add copper
  • Make sure you thoroughly cover all cracks and crevices.  These harbor insects. This oil works by smothering insects and eggs so there must be direct contact with the spray.
Apricots are always to impatient to bloom and usually freeze.

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