Answer: Before launching into a control program I think you should have the problem professionally identified. Hollies can develop fungal diseases but rust is not usually seen, except occasionally in stressed American hollies. I've had experience with leaf miners feeding on my hollies and their feeding can cause rusty colored areas on the leaves but this is a result of dying tissues, not a symptom of rust. So, why not collect a few of the affected leaves, place them in a plastic bag, and take them to your local Cooperative Extension office for diagnosis? Once you know for sure what you're dealing with, you can treat the problem.
Most diseases of holly can be avoided with timely surface watering, maintaining soil fertility and pH, and choosing a holly cultivar adapted to your region so it doesn't have to sturggle to survive. Try to minimize the length of time the foliage remains wet by watering the ground, not the plants themselves, and by promply removing any leaves that show signs of disease.
Best wishes with your landscape.
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