Sweet Bay Magnolia Diseases

Sweetbay flowers bloom in summer, filling the air with gentle floral fragrance.

The sweetbay magnolia, Magnolia virginiana, grows 40 to 60 feet tall with a canopy spread of 15 to 25 feet. The narrow canopy of this semi-evergreen magnolia makes it well suited for planting along roadways and in narrow urban and suburban plantings. Sweetbay magnolia is generally hardy, but some pests and diseases do plague this tree from time to time.

Verticillium Wilt

Verticillium wilt can affect a sweetbay magnolia. This fungal disease lives in the soil and attacks ornamental trees. The fungus spreads through the tree, eventually killing it. A sweetbay magnolia suffering from verticillium wilt displays signs of stress. Leaf yellowing is a sign of verticillium wilt, as are also curling leaves. Symptoms usually appear in summer and worsen as the cold weather sets in. The disease can cause leaves on one section of the tree to wilt.

Scale Insects

Occasionally a stressed sweetbay magnolia tree suffers from scale insects. The tiny insects suck sap from the leaves, often from the underside of the leaf. The scale insects cause leaves to yellow and curl as they draw the sap from the leaf. In a diverse, healthy landscape, natural predators control scale insects. For a small infested tree, you can use insecticidal oils, but it is not a practical solution for a mature sweetbay magnolia. Trees kept well watered are less likely to be affected.

Sassafras Weevil

The sassafras weevil can damage a sweetbay magnolia as it feeds on the leaves. Infestations are rarely deadly and often cause only minor damage. The insects chew the leaves, creating holes 1/6 of an inch around. Adult sassafras weevils and larva both feed on the leaves. Treat small potted or nursery seedlings with insecticidal spray in June and again in July to kill both the larva and the adults.

Fungal Leaf Spot

A variety of fungus attack trees including sweetbay magnolia. The fungus attack the leaves creating circular spots. Depending on the fungus, the spots vary from brown or tan to yellow black and gray. Fungus tend to spread on trees during hot, humid days. The disease is not generally harmful for a sweetbay magnolia although severe infestations can weaken the tree over time. Treat young trees with fungicidal spray at first appearance of fungal leaf spot.

References

• University of Florida; USDA Forest Service Fact Sheet -- Magnolia virginiana; Edward F. Gilman, et al.; October 1994
• University of Florida IFAS Extension Program; Magnolia virginiana 'Henry Hicks'; Edward F. Gilman, et al.
• University of Minnesota Extension; Verticillium Wilt of Trees and Shrubs; Cynthia L. Ash; 2011
• University of Florida IFAS Extension Program; Scale Insects and Mealybugs on Ornamental Plants; Eileen A. Buss, et al.
• Virginia Cooperative Extension; Tulip Tree Leaf Miner; Eric R. Day; May 2009
• University of Illinois Extension; Fungal Leaf Spot Disease of Shade and Ornamental Trees in the Northwest; July 1998