Sooty mould is a group of dark fungi that live on honeydew, the sugary excretion of aphids, whiteflies, mealybugs and soft scales. It grows on the leaf surface without infecting the tissue, but it blocks light and makes leaves and buds unusable (UC IPM).
In practice
Sooty mould is a sign, not the problem: find and control the sap-feeding insect producing the honeydew, usually directly above the blackened leaves. Once the honeydew stops, the mould dries and flakes off over time. Contaminated buds should not be used.
Don't confuse with
- Botrytis: grey fuzzy mould inside buds that rots the tissue.
- Frass: insect droppings as pellets or specks, not a film.
- Necrosis: dead brown tissue within the leaf, not a surface coating.
The sugary liquid excreted by sap-feeding insects such as aphids, whiteflies, mealybugs and soft scales; it makes leaves sticky and feeds sooty mould.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.Soft-bodied sap-sucking insects of the family Pseudococcidae, covered in white waxy filaments, that hide in stem joints and roots and excrete honeydew.Integrated pest management: preventing and controlling pests by combining monitoring, prevention, cultural, biological and, as a last resort, chemical tools against set action thresholds.Botrytis cinerea, the fungus behind bud rot or grey mould, which rots dense colas from the inside in cool, humid conditions late in flower.Insect excrement: the dark pellets left by caterpillars, the tiny black specks left by thrips, and the fine debris left by other feeders; finding it is a key sign of a hidden pest.Death of plant tissue, seen as brown, tan or black patches, spots, tips or margins; it is permanent and the end point of many nutrient, salt, pest, disease and environmental problems.
