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Indoor Lemon Tree Losing Leaves: Fungus and Possible Spider Mites

18-month-old seedling lemon under grow light (Winnipeg) develops yellow spots turning brown, leaves drop. Older leaves affected. Had spider mites on peppers 5 months ago.

Treatment Plan

Watering: Water when dry 1 inch deep; drain saucer.
Remove all spotted leaves – they won't recover.
Spray Ferti-lome Triple Action Plus (neem formula preferred) or horticultural oil (SunSpray) – top and bottom of leaves, weekly until clear.
Test for spider mites: Tap leaf over white paper; moving specks = mites. Triple Action also kills mites.

Consistent treatment saves the tree.

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