Horticultural oil is a highly refined oil, either paraffinic mineral oil or a plant oil such as canola, cottonseed or soybean, mixed with an emulsifier so it spreads in water. It kills mites, aphids, whitefly nymphs, scale crawlers and eggs by smothering them and disrupting their membranes, and it can suppress powdery mildew. It has no residual action once dry.
In practice
Oils are contact tools for veg and mother plants. Coverage of leaf undersides decides success, and repeat sprays are needed to catch hatching eggs. Risks: oils can burn leaves when applied in heat (above about 30 °C / 86 °F), under strong lights, on drought-stressed plants or close to sulfur applicationsbeing reviewed. They should never touch flowers, where they coat trichomes and leave residue. Many oil products are registered pesticides; check what is registered for cannabis locally, and test on a few leaves first.
Don't confuse with
- Neem oil: may contain azadirachtin, an insect growth disruptor.
- Insecticidal soap: fatty-acid salts that break down cell membranes.
- Essential oil sprays: aromatic plant extracts; separate actives with their own rules.
Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth.Small white-winged sap-sucking insects of the family Aleyrodidae, mainly Trialeurodes vaporariorum and Bemisia tabaci, that fly up when disturbed and coat leaves in honeydew.A fungal disease, on cannabis caused mainly by Golovinomyces ambrosiae, that grows as white powdery patches on leaves and buds and thrives in moderate humidity.A mother plant is a female kept permanently in vegetative growth to supply cuttings, so a selected genotype can be propagated as clones indefinitely.Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.An oil pressed from seeds of the neem tree (Azadirachta indica) that smothers soft-bodied pests and, in crude forms, contains azadirachtin, an insect growth disruptor.Potassium salts of fatty acids sprayed to kill soft-bodied pests such as aphids, mites and whitefly nymphs on contact by disrupting their cell membranes.Contact products act only where the spray touches the pest; systemic products are absorbed and move inside the plant, which raises residue concerns in cannabis.A heated vessel that vaporises elemental sulfur to suppress powdery mildew and mites in veg rooms; it carries fire, gas and timing risks and is never used in flower.Sap-sucking insects of the superfamily Coccoidea that settle on stems and leaves under a protective waxy or hard cover; rare on cannabis and usually introduced on other plants.
