Frass is the excrement and feeding debris left by insects. On cannabis the two kinds that matter most are the dark green to black pellets of caterpillars, often found on leaves below a damaged bud, and the tiny black specks of thrips on silvered leaf surfaces (Oregon State University Extension, EM 9626).
In practice
Frass on a leaf below a cola means look inside the bud: budworm caterpillars tunnel in, and their feeding wounds are a common entry point for bud rot. Check daily in flower, gently parting dense colas. Fresh caterpillar frass is moist and green; old frass is dry and dark.
Don't confuse with
- Soil or perlite specks: no pattern, and no feeding damage nearby.
- Sooty mould: a black film growing on honeydew, not pellets.
- Septoria fruiting bodies: tiny black dots inside leaf spots.
The dense, elongated cluster of flowers that forms at the end of a stem or branch; the main cola tops the leader.Helicoverpa zea, a moth caterpillar that bores into developing cannabis flowers outdoors, leaving frass that triggers bud rot; growers call it budworm.Botrytis cinerea, the fungus behind bud rot or grey mould, which rots dense colas from the inside in cool, humid conditions late in flower.Perlite is a light, white, puffed volcanic glass added to growing mixes to increase drainage and air space; it is chemically inert and holds no nutrients.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.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 fungal leaf disease caused by Septoria cannabis that produces tan to grey spots with dark margins and yellow halos, starting on lower leaves.Any disease that causes discrete dead spots on leaves; on cannabis, mainly fungi such as Septoria cannabis and Alternaria, plus some bacteria.The larval stage of moths and butterflies (order Lepidoptera); on cannabis, leaf-chewers, stem borers and bud-boring species whose frass seeds bud rot.Slender insects about 1-2 mm long, chiefly western flower thrips (Frankliniella occidentalis), that rasp leaf surfaces, leaving silvery streaks dotted with black frass.Systematic, regular inspection of plants, traps and roots to detect pests and disease early, identify them correctly and record numbers for decisions.Routine inspection of dense colas in late flower, at harvest and during drying and curing for signs of grey mould (Botrytis cinerea) and other rots.
