What is it? Sooty mould is a fungus that appears as leaves that have been coated in black soot. This grows on the sticky sweet honeydew that is secreted by many sap sucking insects such as mealybug, planthoppers, leafhoppers, psyllids, whiteflies, aphids and scale insects. Where honeydew occurs, sooty mould is often found growing.
Can we live with it? Although sooty mould does not infect plants, it does cause damage by coating the leaves, inhibiting sunlight penetration. This reduces photosynthesis resulting in stunted plant growth. Coated leaves may also prematurely senesce and die, causing premature leaf drop. Fruit or vegetables covered with sooty mould are edible but fruit formation and health can be affected. How is it controlled? Sooty mould and other pest and disease issues often affect plants that are stressed or that lack vigour. When plants lose vigour they become susceptible. Plants become stressed if they are not well fed and watered. Scale and other sap sucking insects infest weak plants, secreting honeydew. Once the plant loses vigour, it becomes vulnerable so the problem becomes even bigger. Spray the leaves with Eco-Oil and repeat weekly to control sap sucking insects. Prune off affected leaves or remove the sooty mould with a solution of mild soap and warm water.