Troubleshooting
Western Spirea problems — and how to fix them
Western Spirea (Spiraea douglasii) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Aggressive suckering
Can spread invasively in ideal moist conditions. Remove suckers promptly at the base to contain spread, or install a root barrier if planting near lawns or borders.
Leaf spot diseases
Brown or black spots on foliage in wet, humid conditions. Improve air circulation by thinning overcrowded stems; rake and dispose of fallen leaves.
Aphids
Clusters on new growth in spring. Natural predator populations generally keep numbers in check; apply insecticidal soap if needed.
Powdery mildew
White fungal patches in warm, dry spells. Water at the base (not overhead) and remove heavily infected shoots.
Crown gall
Warty galls at the base of stems caused by Agrobacterium tumefaciens. Remove and destroy affected plants; do not replant spiraea in the same soil for several years.
Prevent western spirea problems before they start
Most western spirea issues are care-mismatch, not bad luck. Dial in the basics:
Western Spirea problems — FAQ
Why is my western spirea aggressive suckering?
Can spread invasively in ideal moist conditions. Remove suckers promptly at the base to contain spread, or install a root barrier if planting near lawns or borders.
Why is my western spirea leaf spot diseases?
Brown or black spots on foliage in wet, humid conditions. Improve air circulation by thinning overcrowded stems; rake and dispose of fallen leaves.
Why is my western spirea aphids?
Clusters on new growth in spring. Natural predator populations generally keep numbers in check; apply insecticidal soap if needed.
Why is my western spirea powdery mildew?
White fungal patches in warm, dry spells. Water at the base (not overhead) and remove heavily infected shoots.
Why is my western spirea crown gall?
Warty galls at the base of stems caused by Agrobacterium tumefaciens. Remove and destroy affected plants; do not replant spiraea in the same soil for several years.