The Q&A Archives: Black "fungus" On Holly Leaves

Question: The leaves on my 10-year-old female holly are turning black on the west side of the shrub. What could be causing this and what can be done to cure it? It gets full sun for 4-5 hours/day.

Answer: It's likely that the holly is infested with scale insects. Scales suck the juices from the stems and undersides of the leaves of plants. Their excrement is a sticky, sugary substance that falls on the leaves and promotes the growth of bacteria, called sooty mold. This sooty mold is what turns the tops of the leaves black. Inspect your holly for the scale insects and hose them off, or squish them with your fingers. The sooty mold will weather off, or you can wash it off the surface of the leaves.

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