Q: I had some beautiful holly plants in my landscape, but they are covered with disgusting stuff now. It’s black and covers the leaves. I can rub it off with my fingers and water, but it comes back. What is it and how do I get rid of it?
Answer: It sounds as if you have scale insects and sooty mold on your hollies. Scale is a piercing-sucking insect. It feeds on the plant, and the resulting damage can be leaf drop, chlorosis (yellowing), branch die back and possibly plant death.
The black covering is sooty mold. It is the excreted honey-dew from the scale insect. You may not want to wash it off with your bare hands. There are hard and soft scale insects, and a field identification guide is included in the University of Florida publication “Field Key to Identification of Scale Insects on Holly (Ilex spp.)” by Jamba Gyeltshen and Amanda C. Hodges at http://edis.ifas.ufl.edu/pdffiles/IN/IN64900.pdf.
Environmental controls can include horticultural oil, insecticidal soap and/or Neem. Natural controls generally manage this pest and can include parasitoids, predators, pathogens and environmental conditions. Chemical controls may or may not be needed, but should be the last resort. As with any control, read and re-read the directions before you apply.
Lynn Barber is the Florida Yards and Neighborhoods agent at Hillsborough Extension.. Reach her at BarberL@hillsboroughcounty.org.