Answer: Based on your description I am not certain what is happening to your hollies however it is possible there is an infection, for instance tar spot. (Insecticide would not cure a disease problem such as this.) I would suggest you consult with your county extension and/or a professionally trained and certified nurserman to obtain a specific diagnosis of the problem(s) and based on knowing that, decide how best to treat it. They may appreciate a sample enclosed in a plastic bag and possibly some photos, showing the overall plant and some close ups. Here is a photo of tar spot so you can compare. You may need to click on the photo to enlarge it enough to see well.
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