We have a row of 25 year old hollies. About 3-4 years ago, two died and we replaced with new ones. Those two have barely grown in those years and one newer holly is shown in these pictures. This year, I noticed some blackspots and yellowing of leaves on several hollies and treated with copper fungicide that had limited success early-mid summer. As summer progressed, the hollies looked worse and now they over 50% dead. Last year, the next door neighbor told me that some of his shrubs died because of something that his lawn service had used. This spring, we had to pull out and replace two other shrubs on that same side of the yard that had been healthy for years. I want to pull the hollies all out and replace but don't want to invest the money without knowing the source of the problem and a solution. These receive full sun on the south wall of our home. Thanks!
It is difficult to say what is ailing your hollies but we wonder about site issues leading to root problems. Site issues can include soil problems (and we def suggest testing the soil before planting anything else. See: https://www.extension.umd.edu/hgic/topics/soil-testing), poor drainage, reflected heat from the house, mulch depth etc.
Have there been any other chemical applications? (Hollies rarely need fungicides and used incorrectly their leaves can burn.) Fertilizer? Salt/Deicer?
How does the area drain? Hollies will not tolerate wet conditions, which can compromise roots and lead to root rot. Last year's historic rains negatively affected even areas that normally have good drainage, and this year's 9+ weeks of drought are taking out many shrubs and trees that were already struggling.
How deep is the mulch? It should be no deeper than 2-4 inches and always pulled back from contact with the trunks and stems of plants.
Here is our page on tree and shrub problems to explore: