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Indian Bean Tree (Catalpa) Black Fall Leaves: Sooty Mold from Insects

My Tree

Catalpa leaves turn black in fall instead of yellow. Owner wonders if disease or soil issue.

Test: Sooty Mold

Wipe a black leaf with wet paper towel. Black rubs off = sooty mold (fungus growing on insect honeydew).

Source Insects

Aphids
Soft scales
Whiteflies

Check leaf undersides and stems. Treat insects (neem oil, horticultural oil, or systemic); mold disappears when honeydew stops. Compare to sooty mold on gardenia/crapemyrtle images. Local garden center can confirm.

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