Nasty 'fungus' on Japanese magnolias is really scale insects. Dan Gill explains what to do.

My Japanese magnolias have this horrible disease that causes tan-colored growths that look like boils on the branches and attract flies. A black mildew is on the leaves, and the leaves eventually die. What is this and how do I treat it? A copper-based fungicide used for fruit plants has not worked. — Joseph

The problem with your Japanese magnolias is an insect problem, not a disease. The tan growths are magnolia scale insects. They are sucking the sap from the tree. Heavy populations can significantly damage branches and even the overall health of the tree.

As they feed on the sap, the scale insects excrete a sugary liquid called honeydew. This liquid accumulates on the leaves, twigs and branches, and is attractive to flies, wasps, ants and other insects. A group of fungi use the sugary