How to Treat Black Soot on a Magnolia Tree in South Florida

Sooty mold can threaten the magnolia tree's snowy blossoms.

If you have a magnolia tree, you probably love it for its creamy blossoms and glossy foliage. The last thing you want to see is a sooty, dusty-looking black substance coating the flowers and leaves. Unfortunately, magnolia trees, although generally resistant to pests and diseases, are susceptible to a disease called "sooty mold," which grows on the sticky residue produced by scale insects. South Florida, with its warm and humid conditions, provides an environment in which fungal diseases like sooty mold can flourish. In addition to being unsightly, sooty mold can interfere with photosynthesis. But by attacking both the disease and the insects that cause it, you can banish sooty mold from your South Florida magnolia tree.

Things You'll Need

• Pruning shears
• Chlorine bleach
• Garden hose
• Paper towels
• Insecticidal soap
• Commercial insecticide containing dimethoate

Instructions

1. Examine the bark and leaves of the magnolia tree for signs of scale infestation, usually indicated by round, waxy, brownish bumps and the presence of small, blackish insects about the size of sesame seeds. Prune off and destroy any heavily scale-infested branches. Clean the blades between each cut with a disinfectant solution made by mixing 9 parts water to 1 part chlorine bleach.

2. Use vigorous sprays from a garden hose to physically wash the sooty mold from the leaves, wiping them down between sprays with paper towels.

3. Target the scale insects by spraying the leaves and branches with insecticidal soap, being careful to include leaf undersides. The most effective time for using this treatment is in early spring or late August.

4. Spray with a systemic insecticide if sooty mold persists in spite of your efforts. According to the Chase Horticultural Research website, the chemical dimethoate can be effective on sooty mold.

5. Prevent reinfection by pruning your magnolia tree to thin it and open it to increased sunlight and air circulation. This helps create conditions unfavorable to Capnodium, the fungus that causes sooty mold.

Tips & Warnings

• Always read the manufacturer's directions carefully, and follow them exactly, when using an insecticide.

References

• Chase Research Gardens: Sooty Mold
• Florida Department of Agriculture & Consumer Services: Common Foliage Diseases of Florida Hardwoods