Black Leaves on a Southern Magnolia

The evergreen southern magnolia produces blossoms against a backdrop of green foliage.

Southern magnolia trees (Magnolia grandiflora) develop black leaves when infested with the magnolia scale insect (Neolecanium cornuparvum). Highly susceptible to the insects, according to the U.S. Forest Service, the tree does not suffer serious damage but is rendered visually unsightly.

Identification

The magnolia scale attaches its strong sucking mouth to the stems of the magnolia tree to suck its nutrients. The insect covers its body with a waxy, white protective coating. The insects may completely encrust the tree's stems.

Effects

The insect secretes a honeydew-like substance from its body as it feeds on the tree's sap. The honeydew grows a black, sooty mold that renders the leaves and stems of the tree black. The mold attracts an abundance of flies, ants, bees and wasps, according to the Ohio State University.

Prevention/Solution

Apply horticultural oils in late August to control scale insects. Apply dormant oil sprays in October, November and March for control. A wide array of insecticide sprays formulated to effectively kill and control the magnolia scale insect can be applied in late August and September.

References

• U.S. Forest Service: Magnolia Grandiflora
• Ohio State University: Magnolia Scale And Its Control
• University of Kentucky: Magnolia Scale
• Penn State: Magnolia Scale
• Cornell University: Magnolia Scale

Resources

• University of Wisconsin Extension: Magnolia Scale