Using Organic Alternatives for Pest Control Like Dormant Oil

Using Organic Alternatives For Pest Control Like Dormant Oil

With all of now using organic and non-chemical techniques for pest control – this becomes a critical time of year if you have not yet applied dormant oil. Dormant oil controls aphids, scale, spider mites, and many other insects by desiccating or smothering eggs and larvae.

These sprays are applied usually between November to late March or early April …If your trees or shrubs have not yet leafed out then there is still a little time (but not much). Do not apply if the tree or shrub has leaves.

Most trees and shrubs will benefit from dormant spray. Fruit trees, raspberries, junipers, roses, and many flowering shrubs probably benefit the most. The main insects you can control with dormant spray are; aphids, blister mites, bud mites, scale, pear psylla, peach twig borers, lygus bugs, and many other insect’s eggs. Honeylocust mite, European red mite, and spruce spider mite are controlled with dormant oil sprays, because they overwinter as exposed eggs on plants. Dormant oil sprays do not kill two-spotted spider mite, as they overwinter on the ground in leaf debris.

Spray the upper branches, twigs and trunks of trees with dormant spray. Try not to not to spray the lower trunks with dormant spray because many beneficial insects lay their eggs in the lower parts of the tree.

Apply only when trees are dormant, November through March, after all the leaves have fallen. Mix with water as directed and spray to all surfaces of the trunk, branches and twigs. Apply when the temperature is expected to rise during the day; temperatures below 35 degrees can damage the bark. Spray the branches thoroughly; to the point of dripping. You may need 4 or 5 gallons of dormant spray to completely cover a large tree. Spray junipers, and other shrubs, thoroughly from top to bottom, to prevent many insects, such as scale or spider- mites.

Dormant Spray Kit – FIRST SPRAYING (MARCH)

Best applied to fruit trees, roses, ornamental shrubs like Highbush Cranberry and European Snowball, Evergreens such as Cedars, Green Junipers, Euonymus and trees like Hawthorn, Crab Apple and Honey Locust.

Use Horticultural Oil and Lime Sulphur in combination. Apply to dormant trees before buds start to grow in spring. This is a very important application as it destroys many insect eggs on the bark, overwintering adult insects and prevents many diseases.

Do not use Horticultural Oil on Sugar Maple, Japanese Maple, Beech, Butternut, Colorado Blue Spruce, Douglas Fir, Hickory, Holly and Walnut. Horticultural Oil will damage the bark on Empire, Mitsu and Red Delicious apple trees.

Do not use Lime Sulphur on Apricot. Do Not use Lime Sulphur on Plum trees when they are in leaf.

The horticultural oil kills exposed insects and mites by either suffocating them or by directly penetrating the outside cuticle and destroying cells. Spraying trees with dormant oil after bud break and leave have emerged will still control the pests but it may kill the young leaves or cause leaf edges to turn black.


  • Spray in the morning to allow quick drying of the spray before evening. Do not spray if any chance of frost.
  • Injury may occur to tree if spray is not completely dry before a cold night.
  • Choose a day when temperatures will remain at 0°C or above for a minimum of 24 hours. Do not spray in temperatures below 4°C nor any temperature above 27°C.
  • Only 1 application is necessary with this combination spray before buds start to swell.
  • Lime Sulphur may be used alone during the growing season; read instructions carefully before use.
  • Do not spray in windy conditions.
  • Do not let any mixture fall or drift onto hard surfaces as interlock, natural stone, brick, concrete, stucco, wood or aluminum siding as it may leave a permanent stain. If necessary, cover area with plastic and then spray.
  • Best to use protective clothing and wash hands and face after use.

You can mix the spray is a 2 parts (Lime Sulphur) to 1 part (horticultural oil) ratio.

Mix 120ml (8 tablespoons) of Horticultural Oil and 60ml (4 tablespoons) of Lime Sulphur in 3 litre of water and spray all bark thoroughly from top to bottom. Make sure all twigs and crevices in bark are covered. Mix only what you can use as you cannot save the prepared solution for later use.

For the entire kit, mix 500ml Horticultural Oil + 1 litre Lime Sulphur in 25 litres (5 ½ gals. of water).

For roses, be sure to spray the soil around the base of the plant as well to control Powdery Mildew and Black Spot.

To use a DIAL-A-SPRAY hose end sprayer, mix 150ml of Horticultural Oil with 300ml of Lime Sulphur. DO NOT ADD WATER. Set the dial at #60, attach to garden hose and spray.

Insects & Diseases

The following may be controlled by the application of Horticultural Oil / Lime Sulphur Combination

SCALE – Attacks apple, peach, pear, plum & cherry. Tiny insects under scales that cause damage by sucking sap from the leaves and tender branches of the tree. MITES -Attack apple, peach, pear, plum, & cherry. spider like insects which siphon sap from leaves, spinning microscopic webs. PEAR LEAF BLISTER MITE – Causes dark dead spots and leaves, eventually weakening the trees overall health. PEAR PSYLLA – Sap sucker, which causes excrement (honeydew) to turn black and sooty. Leaves turn pale with dead areas, eventually damaging fruit and weakening tree. APPLE SCAB -A disease that causes dark spots on leaves and fruit. Leaves may droop and the crop may be reduced the following year. BLACK KNOT – An extremely infectious disease for Prunus trees causing hard, crusty, black swellings several inches long on branches and small twigs. PEACH LEAF CURL – Causes foliage to curl and form reddish blisters on leaves. They eventually turn yellow and drop, weakening the tree. POWDERY MILDEW – The white, powdery mildew turns to a brown felt-like coating on foliage, twigs and fruit. RUST / FUNGUS – Orange spots, later growing into pimple like lesions that appear on lower leaf surfaces. ANTHRACNOSE -Affects canes on Raspberries, causing discolouration and cracking of bark, resulting in spoilage of fruit. SPUR BLIGHT -A disease which attacks canes of Raspberries. Canes may be weakened and killed overwinter.