Circling, curling and distorted leaves could be the start of powdery mildew infestations. The leaves start curling sometimes and after that, you see the leaves sporting what looks like talcum powder dust. Keep an eye for additional symptoms to confirm or apply controls now.
You can prevent this problem by using PM resistant cultivars, water the soil early in the mornings and never the leaves, keep the area under the shrub clean of plant debris, allow some separation between any two plants to improve air flow. Affected leaves that have fallen and all plant debris should be disposed in the trash, not in the compost pile. In severe infestations, consider replacing the mulch.
You can treat PM using Neem Oil Sprays, regular milk sprays (1-2 parts milk, 9-8 parts water, 1/2 teaspoon of liquid soap) or a baking soda spray (1 tbsp of baking soda, 1/2 teaspoon of liquid soap, 1 gallon of water).
Complete browning of leaves without any other symptoms may be due to insufficient moisture; spider mites; salt burn; too much fertilizer.