Answer: Japanese hollies can develop fungal diseases if the growing conditions aren't quite right - too much shade, poor air circulation, etc. Pruning them back should help remove the fungus and also open them up to better air circulation, which should prevent additional fungal diseases. But they are also subject to insect feeding from aphids, scales and mealybugs. When these pests feed they exude a sticky substance called honeydew. When it dries it turns black which can look like a fungus, but it's really just a light coating on the surface of the leaves below where the insects were/are feeding. Be sure to check for insect pests before assuming anything on the leaves is a fungus. As a rule hollies take well to pruning and will grow new stems and leaves a few weeks after being pruned. Give your hollies a chance to recover from their pruning and be sure to inspect them for insect pests.
Hope your shrubs recover soon!
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