Spider mites
Almost invisible without a hand lens. Yellow-green to red-orange specks running along the underside of each palmate leaf. Fatsia's broad 7 to 9-lobed leaves give mites huge feeding surfaces, and dry winter heating air triggers a population boom.
Pale tiny pale dots that quickly progresses to a visible bronze cast across the upper leaf face. Fine webbing strung between lobes near the central petiole junction. Heavy infestations dull the glossy finish and cause whole leaves to yellow and drop.
Shower the leaves weekly for 3 weeks
Move the fatsia to the shower. Spray cool water on the underside of every leaf for 60 seconds, tilting each palmate leaf so water reaches the central lobe junction. Fatsia's thick glossy leaves take a hard spray well. Repeat weekly for 3 weeks.
Neem oil at lights-out, every 5 days for 3 rounds
Mix 2 tablespoons cold-pressed neem oil and 1 teaspoon dish soap per gallon of water.
Spray top and bottom of every leaf at lights-out, lifting each palmate leaf to coat the underside where mites cluster.
Repeat every 5 days for 3 rounds. That covers the full egg-to-adult cycle.
Raise humidity above 50%
Run a humidifier near the plant for 50 to 60% relative humidity through winter. Fatsia comes from humid Japanese coastal forests and prefers the moisture anyway. Hot dry indoor heating is the climate mites need to breed fast on the broad leaf surfaces.
Pyrethrin sprays from the hardware store kill them.
Spider mites are arachnids, not insects, so most household bug sprays barely affect them. Use neem oil or a true miticide instead. Fatsia's tough glossy leaves tolerate horticultural oil too if neem isn't enough.
