Scale insects are sap feeders of the superfamily Coccoidea. After a short mobile crawler stage, most settle in one spot and grow a cover: soft scales (family Coccidae, such as brown soft scale, Coccus hesperidum) produce a waxy dome and honeydew, while armoured scales (Diaspididae) build a hard, detachable shield and do not make honeydew.
In practice
Scale is unusual on cannabis because the crop cycle is short, but long-lived mother plants kept beside houseplants can pick it up. Signs are small brown or grey bumps along stems and leaf veins that do not move, plus sticky honeydew and sooty mould for soft scales. Crawlers are the vulnerable stage; adults under their covers shrug off most contact sprays. Horticultural oil in veg, physical removal and parasitic wasps are the usual tools. Badly infested mothers are often easier to replace from a clean cut. Check what is registered for cannabis locally.
Don't confuse with
- Mealybugs: white and fluffy, still mobile as adults.
- Aphids: soft, mobile, breed fast.
- Leaf spot lesions: part of the leaf tissue; scales can be lifted off.
The mobile first-instar nymph of a mealybug or scale insect; the only stage without protective wax, so the stage contact sprays hit best.The sugary liquid excreted by sap-feeding insects such as aphids, whiteflies, mealybugs and soft scales; it makes leaves sticky and feeds sooty mould.A mother plant is a female kept permanently in vegetative growth to supply cuttings, so a selected genotype can be propagated as clones indefinitely.A black, soot-like fungal film that grows on the honeydew left by sap-feeding insects; it does not infect the plant but blocks light and signals an aphid, whitefly, mealybug or scale problem.A refined petroleum or plant oil sprayed to smother soft-bodied pests and eggs and suppress powdery mildew on contact; used only on foliage, never on flowers.Tiny parasitic wasps of the genus Aphidius that lay eggs inside aphids; the larva kills the host from inside, leaving a swollen tan mummy.Soft-bodied sap-sucking insects of the family Pseudococcidae, covered in white waxy filaments, that hide in stem joints and roots and excrete honeydew.Any disease that causes discrete dead spots on leaves; on cannabis, mainly fungi such as Septoria cannabis and Alternaria, plus some bacteria.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.Holding incoming plants, clones or seeds apart from the main grow, under observation and sometimes treatment, until they are shown to be free of pests and disease.
