Posted: 26/03/2015 at 16:45
Small, sucking insects such as scale, whiteflies and aphids secrete a sweet sticky substance called honeydew when they feed. Within a few days, honeydew becomes infested with sooty mold. The best way of controlling sooty mold is to control the insects that produce honeydew.
The only way to keep the mold from returning is to treat the cause of the problem.
"Clean all affected needles, leaves, stems and twigs with a spray made of one teaspoon of liquid dish detergent mixed with a gallon of water. This not only removes sooty black mould, but also helps to control the aphids and scale that can cause it. Spray on the undersides of leaves as well in order to target aphids where they live. Rinse affected shrubs with forceful blasts of water from a garden hose to not only clean off residual soap solution but physically knock off aphids and mealybugs."