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.
