Verticillium Wilt in Magnolia Trees

Verticillium wilt is a serious disease that damages more than 300 different plant species from many different families, including magnolia trees. This fungus, which lives in the soil, is difficult to control.

Features

The Verticillium dahliae and Verticillium albo-atrum fungi species cause verticillium wilt in magnolia trees. The fungus infects soil through wind, seeds, water, contaminated pruning tools and on the roots of transplanted plants. It enters magnolia trees through the feeder roots or through lesions in the root system.

Effects

The fungus penetrates the vascular tissues and the vessels that conduct water through magnolia trees. It produces spore-filled gums that clog the tissues, which restricts the water flow and causes wilt. Infected magnolia stems and branches have circular dark green or brown stains on the inner wood. The leaves yellow and infected branches die. Young trees often succumb within the first season; other trees die more slowly, section by section.

Prevention/Solution

The Missouri Botanical Garden indicates that fungicides are rarely effective against verticillium wilt. Plant verticillium-resistant varieties such as the Kobus magnolia, and prune out damaged areas of existing trees. Sterilize pruning equipment to prevent spreading the infection from one tree to another.

References

• University of Illinois Extension: Verticillium Wilt of Magnolia
• University of Illinois Extension: Verticillium Wilt Disease
• Cornell Cooperative Extension: Verticillium Wilt
• Missouri Botanical Garden: Verticillium Wilt
• City of Seattle: Trees for Future Planting in Volunteer Park