Magnolia Tree Decline: White Bark Growth and Leaf Spots in Fort Worth

Diagnosing Magnolia Symptoms: Insects vs. Disease

A Fort Worth homeowner reports one of two magnolias developing a white, fungus-like bark coating, thinning canopy, and dark leaf spots. A tree trimmer recommended spraying "Sevin" (carbaryl) top to bottom.

Likely Culprit: Insect Infestation

The white coating suggests an insect issue—possibly magnolia scale, aphids, or bark lice (psocids)—rather than a primary fungal pathogen. These insects excrete honeydew, which hosts sooty mold (dark spots). Sevin is an insecticide, which aligns with this diagnosis.

Recommended Action

1. Verify Diagnosis: Contact Fort Worth Urban Forester Courtney Blevins (817-926-8203, cblevins@tfs.tamu.edu) for a site visit. This free state service ensures accurate identification.
2. Targeted Treatment: If scale or aphids, horticultural oil or systemic insecticides (e.g., imidacloprid) are often more effective and safer for beneficials than broad-spectrum sprays.
3. Avoid Unnecessary Sprays: Indiscriminate Sevin application harms pollinators and predators.

Drought stress likely predisposed the tree to infestation. Address watering and mulching as part of recovery.