What’s the problem?
The leaves of my 40-year-old rubber plant are speckled with tiny black dots, turning yellow, and many are dropping off. New shoots are still growing, but the older leaves continue to fall.
Diagnosis
The black dots you’re seeing are most likely thrips droppings. These tiny insects puncture the leaf surface to drain sap, resulting in silvery streaks, mottled patches, curling and eventual leaf drop. They thrive in warm, dry conditions and are easily introduced when plants are moved outdoors. Once inside, they spread rapidly, particularly on mature, leafy specimens. Their damage is often mistaken for nutrient deficiencies or sun scorch, but the telltale sign is the combination of silvery streaks with tiny black specks.
Prescription
Begin by gently wiping leaves with a damp cloth to remove droppings and any insects. Next, spray thoroughly with pesticide, and repeat weekly to interrupt the life cycle. Persistence is key, as thrips eggs hatch quickly. For a large and highly valued plant like yours, biological control agents such as predatory mites (for example, Amblyseius cucumeris) can be introduced to reduce thrips populations naturally.
Prevention
Inspect plants regularly, paying close attention to new leaves, especially the undersides, where thrips tend to hide. Increase humidity, as thrips prefer dry air. If you move plants outdoors in summer, isolate them for a fortnight before returning them indoors to avoid hitchhikers spreading through your collection.
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