Berberis thunbergii · Shrub
Berberis sawfly: Hand-pick larvae if few, or apply a biological insecticide like spinosad for severe infestations.
Powdery mildew: Improve air circulation by pruning and apply a fungicide if infection is severe.
Aphids: Encourage natural predators like ladybirds or use a strong jet of water to dislodge them.
Honey fungus: Improve drainage and remove infected roots; severe cases may require removing the plant.