The dim light and short days of winter can push some houseplants over the edge, energy-wise. Without enough light energy to produce protective chemicals and bug-thwarting cell structures, the few mealybugs, spider mites or fungi that are always present can easily become legion. You'll approach your rubber tree one day, only to freeze with watering can raised. You'll say, "Yuk!" when you see all the shiny, sticky honeydew on the leaves below the fuzzy gray-white mealybugs that produce it.
Those insects are sucking sap from the plant, weakening it further.
We've written about this before and since our motivation for having this website was to avoid having to re-write, here's a summary and a referral:
You can help by washing the plants off in the shower or with a soapy cloth. However, it's better to help your plants fend pests off by their own internal means so the critters cannot multiply. Clean the plants before they get into trouble and make sure they are in the brightest light possible, near a window or under a grow light.
What's Coming Up 77: Download this pdf edition to read "How bathing a mealybug will save a kumquat."