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Mineral oil (horticultural oil)

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Mineral oil may be used to control various pests, including scales
Photo: Jardin botanique de Montréal (Pascale Maynard)

Caution
The information below is intended only as a guide. Always read product labels carefully.

Product description

Pesticides with mineral oil as the active ingredient are used as insecticides and acaricides for treating trees and shrubs. They are available as concentrates to be diluted before use.

Target pests 

Products with mineral oil as the active ingredient may be used to control various pests, including:

NB: The product label lists the plants on which the pesticide may be used, along with the target organisms. 

How it works

Mineral oil may act on pests in a variety of ways:

  • by blocking their respiratory systems
  • by destroying the waxy coating on their bodies
  • by interfering with their feeding
  • by discouraging them from laying eggs (repellent effect)

It can also smother eggs laid on plants.

Application

The product must be mixed with water and sprayed on. Because the mixture tends to separate, it should be shaken well before and during treatment.

Thoroughly spray all parts of plants to be treated, without run-off.

The product may be used during dormancy (in spring, before buds open) or in a lower concentration during the growing season.

During dormancy, the oil may be combined with calcium sulphide or calcium polysulphide (lime sulphur), following the directions on the label. During the growing season, allow at least 30 days between an application of mineral oil and treatment with lime sulphur or sulphur.

Ideally, the product should be sprayed on in the morning, to allow time for it to dry. It should not be applied:

  • if there is a risk of frost or rain within 24 hours
  • during very humid weather
  • to plants suffering from drought
  • during very hot weather (above 27°C)

Precautions

The pesticide may irritate the respiratory tract, skin and eyes, so it is best to wear a mask, gloves, long sleeves and pants and goggles when applying it.

It may be toxic to some plants (phytotoxic), including:

  • beech trees (Fagus spp.)
  • Douglas fir (Pseudotsuga menziesii)
  • hickories (Carya spp.)
  • hollies (Ilex spp.)
  • some apple cultivars (Malus spp.)
  • sugar and Japanese maples (Acer saccharum and Acer palmatum)
  • walnut trees (Juglans spp.)

Signs of phytotoxicity may include yellow leaves, darker spots where the oil remained for a longer time and early dropping of leaves. If in doubt, it is best to spray a small area of the plant and wait 24 to 48 hours to see how it reacts.

The needles of conifers with bluish foliage may turn green after treatment. New shoots will be a normal colour, however.

Do not use near any body of water or wetland, or dump any pesticide or rinse your equipment there, as this will contaminate the water. Never dump pesticides down sewers.

Keep out of reach of children.

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