Diagnosing and Treating Hackberry Tree Decline: Sooty Mold, Insects, and Squirrels

What's Wrong with Your Hackberry?

A large hackberry showing blackened leaves, thinning canopy, and sticky residue is likely suffering from an insect infestation—specifically aphids or scale insects. These pests suck plant sap and excrete honeydew, a sugary substance that coats leaves and branches. A black fungus called sooty mold then grows on the honeydew, giving the tree its dirty, blackened appearance.

Identifying the Culprit

• Aphids: Small, soft-bodied insects clustering on leaf undersides and tender shoots.
• Scale insects: Immobile, shell-like bumps on twigs and branches; often overlooked until honeydew appears.

Both produce honeydew and lead to sooty mold. The "galls" mentioned may have been a separate issue (possibly hackberry nipple gall), but the current symptoms point to sap-feeders.

Treatment Options

Systemic Soil Application (Recommended for Large Trees)

For a mature hackberry, spraying the canopy is impractical. Instead, use a systemic insecticide applied to the soil:

• Product: Imidacloprid (e.g., Bayer Advanced Tree & Shrub Insect Control).
• Timing: Apply in early spring as leaves emerge. Fall application is less effective because uptake slows in dormancy.
• Method: Mix per label (based on trunk diameter) and pour around the base. Roots carry the insecticide to the foliage.

Contact Insecticides (If Spraying Is Feasible)

For smaller trees or targeted treatment, foliar sprays with acephate, bifenthrin, malathion, or insecticidal soap can work. Rotate chemical classes if resistance is suspected.

Fertilization for Recovery

Stressed trees benefit from fertilization to rebuild vigor:

• Apply 10-10-10 fertilizer at 1 lb per inch of trunk diameter, scattered under the canopy.
• Water in well, or apply before rain.
• Fertilize in fall and again in spring.
• Avoid "weed and feed" products—they contain herbicides that harm trees.

Squirrel Nests

Squirrels are a nuisance but not the primary cause of decline. If removal is desired:

• Live-trap and relocate (check local wildlife regulations first).
• Nests will disintegrate naturally once squirrels are gone.
• Do not attempt to remove nests from a large tree—dangerous and unnecessary.

Summary

The black leaves are sooty mold from honeydew-producing insects. Treat with a spring soil systemic, fertilize to boost health, and manage squirrels if needed. The tree can recover with proper care.