disease of holly bushes

Question

Along my driveway are some holly bushes planted as a hedge approx. 3-4 ft. high and a large section lower down (bottom 2 ft.) is being covered by what appears to be (or I assume) is a spiderweb and the leaves are turning black. But I see no signs of spiders or other bugs and nothing seems to get trapped in the web like normally seen with spiders. All sources I see mention spiders, mites, blights, etc. common to hollies but they don’t match the description or symptoms of my bushes. Area affected was about 12-18 in. Across last year but is now near 3 ft. Wide. Any insight would be a help.

Answer 1

I would definitely check for pests, in particular mites. They will be very small and will be on the underside of the leaves. When you see webbing, it is usually from mites. This article will help with treatment:
https://www.gardeningknowhow.com/plant-problems/pests/spider-mite-treatment.htm

As for the black leaves, this sounds like either tar spot or sooty mold. Sooty mold is normally a result of a pest infestation, and the most likely in your case. These articles will help: https://www.gardeningknowhow.com/ornamental/shrubs/holly/holly-problems-holly-leaf-spot-or-holly-tar-spot.htm
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm