Black scum on holly

Ita Ryan asked 6 years ago

I have a variegated holly with black kind of scum on the leaves. The holly is 4 foot tall doing well but should I be worried?

1 Answers

Gerry Daly Staff answered 4 years ago
This sounds like sooty mould that grows on the exudate of greenflies. Apparently greenflies cannot digest some sugars and these are excreted.

The fungus sooty mould grows on the sticky layer. The greenflies or scale insects, which is a similar sap-sucker, will eventually be controlled by their natural enemies and the tree will grow out of it.