Black mold on holly tree
Hi I have a holly tree that has black mold covering all of the leaves. It sits in the front yard with plenty of sun. We recently bought the house in November, and have not noticed this. We recently had the tree trimmed by a landscaper this spring and this is when I started to notice it. I am not sure how long the mold has been around. My research indicates that I need to identify the pest to determine the best treatment method. The only pest that I have seen multiple times is the chilocorus stigma, otherwise known as the twice-stabbed lady beetle. Attached you will find pictures of the leaves and the beetle. The tree is not completely covered with these beetles, but again is the only insect that I can find. So the questions are: Could this insect be causing the honeydue and black mold? If so what do I do to get rid of the pest? How do I best get this mold off of the leaves after the pest is eliminated? Thank you for your assistance.
Montgomery County Maryland
Your research saying that you must first identify the pest accurately before treating is great and important and we are so glad you contacted us.
The lady beetle is being maligned however, and is not a pest at all but a beneficial insect which is helping you with control of a different, true pest.
The black coating on the leaves of your holly is referred to as sooty mold. This mold is indicative of a sucking insect, in this case a soft scale. Scale insects look nothing like what we call insects, and in fact spend most of their life settled, covered, and sucking plant sap. They then exude a sweet liquid called honeydew, which drips on the leaves below. Sooty mold grows on that honeydew. The photo you sent of the underside of the leaf is the actual scale insect, which is oval, and the white cottony wax ovisacs trail behind it. This is cottony camellia scale. You can use a winter/dormant rate of oil in the winter. You could also monitor for crawlers (the mobile stage) which begin to appear in mid-June on the leaves. If there are not a lot of ladybugs feeding on them at this time, you can apply an insecticidal soap or summer rate of horticultural oil to leaf surfaces.
We do not recommend other pesticides, so as to protect the beneficial insect populations.