Answer: Hydrangea leaves can develop rust if the plant is under stress because of growing conditions. To avoid rust, increase the air circulation within and around your plant, and avoid overhead watering. Hydrangeas grow best in morning sun and afternoon shade. You can pick off the infected leaves (be sure to rake up any fallen leaves) or you can use a fungicide on your plant. Rust rarely kills a plant and you can keep it from coming back next year by making sure the plant has adequate fresh air circulations (prune if it gets too dense and thick), and if you keep water off the leaves.
Best wishes with your garden!
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