Recently some parts of my 15-year-old holly shrubs (about 3 ft high) have been dying out. On other holly shrubs (I have a total of 6), there is a white substance on the underside of leaves. Last fall, and again this spring, I applied Holly Tone but perhaps not in enough quantity. I love the holly shrubs and want to save them.
Diseases of Holly Shrubs
Certified GKH Gardening Expert
It sounds like you may have pests, perhaps scale or mealybugs. I would recommend neem oil. I have found it to be very effective against these pests. Here is more information on it: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm