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sooty mold

Q: My holly is covered with a black, flaky coating on the leaves and stems. What is wrong with these plants?

Q: I have holly bushes all around my house and they are all doing fine except in one area the holly is covered with a black, flaky coating on the leaves and stems. The area where the plants are doing badly is very wet and doesn’t get as much sun as the other parts of the house. What is wrong with these few holly plants?

A: Without realizing it, you have answered your own question. The holly receiving sun and good air circulation are in the correct place.  That is why they are doing so well. The black coating you see on the other holly is called sooty mold and is the result of a honeydew excretion from insects. In fact, after examining a few stems I found 3 different kinds of scale insects on the stems and leaves. If at all possible, mechanically remove as much scale as possible from the stems and undersides of the leaves. Spray the underside of the leaves and stems of the shrubs with insecticidal soap; be sure to follow the directions on the label. You will probably need several applications of soap to get the plants back to a healthy condition. These holly shrubs will not get better until they are moved to a place where they receive better sunlight and air. Root prune the shrubs approximately 10-12 weeks prior to the transplanting date then dig up a foot or more outside where they were originally root pruned. Dig a plant hole 2-3 times the width and 90% of the depth of the root ball. Add nothing to the new hole site (no fertilizer or amendments). Water the plant appropriately, which is 1-2 gallons of water per inch of trunk caliper directly to the root ball. It may take the shrubs 3-4 months to get established so continue to water regularly through the spring and summer.