I have five holly bushes in the front yard, which have been there for about 14 years and have always done well. While trimming today, I noticed the top of the leaves had almost a 'tar' look and the bottoms where covered in a white 'chunky' substance. When you rub the leaves and branches, it flakes off. My bushes are covered in this and it is killing some of the plant. What do you think this is? And what can I get to fix the problem?
Holly Bush Disease
Certified GKH Gardening Expert
It sounds like sooty mold, which is a symptom of several kinds of pests that can attack hollies. I recommend treating the plants with neem oil. This will kill any pests on the plant and treat the sooty mold as well. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm