Mahonia plants are evergreen shrubs with stiff, leathery leaves that resemble holly leaves. They have fragrant yellow flowers in late winter to early spring, followed by red, blue or purplish-black berries. hinese Mahonia (Mahonia fortunei) has bluish-green foliage and grows 3 to 5 feet wide and tall. Japanese Mahonia (M. japonica) grows 6 to 10 feet tall and Oregon Grapeholly (M. aquafolium) grows 3 to 7 feet tall. Both have dark green leaves.
Mahonia plants grow best in partial shade to full shade and rich, well-drained acidic soil. They are subject to heat stress and leaf burn in full sun. Mahonia plants do not tolerate soils that are alkaline, compacted, wet or clay-based. They are susceptible to winter burn in open, exposed areas.
Mahonia rust and other fungal diseases cause leaf spots. Yellow, orange or reddish masses of spores form on the underside of the Mahonia leaves. The upper side of the leaves turns yellow or brown, and may fall off prematurely.
Gray mold caused by the fungus Botrytis, forms a gray fuzzy mass on affected areas. The mold causes blight of stems, leaves, buds, flowers and fruit. Another fungi that grows in dead wood causes wood rot, which is characterized by stemmed or shelf mushrooms. Some affected plants do not show any symptoms.
Mealybugs and deer brush whiteflies are sap-sucking insects that secrete honeydew. Sooty mold is a fungus that grows in the honeydew. Greenhouse thrips are also sap-sucking insects. Affected leaves appear bleached and have black specks of excrement on the undersides. Finally, bayberry loopers are caterpillars that feed on the leaves.