How to Treat Black Scale on Magnolia Trees


Black scale that infests magnolia trees can cause yellowing leaves, branch and stem dieback, and often leads to sooty mold disease. Sooty mold is a fungal disease that turns the leaves black with mold growth. The scale insect feeds on the magnolia tree's sap and secretes a sticky liquid, called honeydew, onto the leaves and branches. The honeydew allows the black sooty mold to grow and multiply on the magnolia tree. Heavy scale infestations and black sooty mold infections can debilitate the magnolia tree severely and, if left untreated, kill the tree.

Step 1

Remove and destroy any heavily-infested branches on your magnolia tree. Clear away all fallen leaves and discard them to prevent the spread of disease. Disinfect your pruning tools before and after using them on the infested tree by dipping them in a solution of three parts denatured alcohol and one part water.

Step 2

Spray the magnolia tree's leaves and stems thoroughly with a horticultural oil, or "summer oil," at 1.5 to 2 percent concentration. Perform this application in late August, when the scale "crawlers" have become well-established in the tree.

Step 3

Spray the leaves and stems thoroughly with dormant oils in October or November. Apply the dormant oils again in March, before the buds begin to swell, to kill any nymphs that survived the winter season.

Step 4

Treat the magnolia tree with an appropriate insecticide or insecticidal soap in late August or early September, instead of using the horticultural oils. Follow the directions on the insecticide label exactly.

Tips and Warnings

  • If you choose to apply an insecticide to treat the scale infestation, you must apply the chemical when the scale insects during the active "crawler stage," usually in late summer. Don't apply the insecticide before the crawlers emerge or after they've become dormant for the winter. Always wear gloves and eye protection when handling and spraying insecticidal chemicals.

Things You'll Need

  • Pruning tools
  • Denatured alcohol
  • Horticultural oil
  • Dormant oil
  • Insecticide or insecticidal soap (optional)
  • Gloves
  • Eye protection
  • Parasitic wasps or ladybugs (optional)


  • Magnolia Scale

Who Can Help

  • University of Rhode Island Landscape Horticulture Program: Scale Insects
  • Iowa State University Extension: Magnolia Scale Insect
Keywords: treat magnolia scale, black sooty mold scale, magnolia tree scale

About this Author

Sarah Terry brings 10 years of experience writing novels, business-to-business newsletters, and a plethora of how-to articles. Terry has written articles and publications for a wide range of markets and subject matters, including Medicine & Health, Eli Financial, Dartnell Publications and Eli Journals.