What's eating my mahonia aquifolium apollo?

Mahonia aquifolium 'Apollo' is most seriously damaged by berberis sawfly (Arge berberidis), whose larvae can completely defoliate plants through multiple generations from May to October. Rust fungus causes red spots on leaves and is a common secondary problem. Aphids may colonise new growth. The spiny holly-like foliage provides some protection from deer browsing.

Pale grey, black-spotted larvae skeletonise then completely devour leaves; repeated generations between May and October can cause total defoliation. Check plants regularly from May; pick off larvae by hand when colonies are small. Spray with pyrethrin or spinosad if numbers are high. Two or three generations may require repeat treatments.

Soft-bodied insects cluster on young shoots, causing leaf curl and sticky honeydew that attracts sooty mold. Apply insecticidal soap or neem oil; encourage natural predators. Blast off with water jets for light infestations.

Dark red marks appear on the upper leaf surface; powdery orange-brown spore pustules form on undersides — a disease but frequently misidentified as pest damage. Remove and destroy affected leaves promptly. Improve airflow by pruning. Apply copper-based or systemic fungicide if severe.