Q: I was trimming up one of my holly plants and noticed these furry white blobs on the underside of some of the leaves. Can you tell me what it is and or if it is harmful to the plant?
A: It’s cottony camellia scale. This insect attaches itself to the bottom of holly leaves and sucks sap. If there are lots of scale in one spot, they secrete enough honeydew to cover nearby leaves with “syrup” on which black mold will grow.
Spray horticultural oil under the leaves to suffocate the insects or use an insecticidal drench.