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Walnut Aphid Honeydew: Sooty Mold on Leaves

Black leaves on lower walnut branches = sooty mold growing on aphid honeydew. Aphids suck sap, excrete sugar; mold grows on sugar. Not fatal for mature trees.

Diagnosis Confirmation

Sticky residue on leaves/under tree
Black coating wipes off (mold, not leaf tissue)
Ants often present (farm aphids for honeydew)
Lower branches = aphid preference

Management Reality

Spraying large walnuts impractical
Late season = leaves falling anyway
Pruning dead branches doesn't affect aphids
Natural enemies usually control by next year

If Treatment Desired

Systemic imidacloprid soil drench next spring. But mature walnuts tolerate aphids—honeydew nuisance is main issue. Rake leaves to reduce overwintering.

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