See:
Cause A fungus, Chrysomyxa arctostaphyli, which requires an alternate host (spruce) to complete its life cycle. Moisture on leaves favors infection. The fungus spreads by windblown spores. Spread of basidiospores from the Arctostaphylos host to the Picea host appears to be within 984 feet (300 m) which has been the distance suggested to rogue these plants from nearby spruce.
Symptoms Purple leaf spots may be seen 6 weeks after infection. In late spring, the undersides of leaves develop an orange to brownish powdery coating of teliospores. Severe infections can cause leaves to drop. This rust fungus also causes a broom rust of spruce. Infected spruce trees develop large golden yellow witches' brooms, which may be up to 6 ft high.
Cultural control
- Avoid overhead watering.
- Pick off and destroy infected leaves when practical.
- Rake and destroy fallen leaves under infected plants.
- Remove infected spruces from vicinity of desired kinnikinnick plantings, and vice versa.
Reference Ziller, W.G. 1970. Studies of western tree rusts. VIII. Inoculation experiments with conifer needle rusts (Melampsoraceae). Canadian Journal of Botany 48:1471-1476.