CHARLESTON, W.Va. -- A friend wrote recently to ask about a bug problem with some of her potted plants that live outside in the summer but overwintered in the house.
"So my plea for help: I brought my plumbago and hibiscus inside for the winter. Recently I noticed really small white bugs on the underside of the leaves. Do you know what they are and, more important, how can I get rid of them?"
I think there are two possibilities for her pests.
My guess is it's either whiteflies or scale, or both. The whiteflies are obvious. The scale insects appear as small, raised bumps on the underside of the leaves. The scale insects secrete a sticky substance called honeydew.
To get rid of scale, you have to thoroughly drench all leaf and stem surfaces until they are dripping wet. It is also best if you repeat this treatment all over again in five to seven days to catch any crawlers (the translucent young ones) that you missed the first time. After that, you should check your plant weekly to see if they return.
The best nontoxic treatment for mealybugs and scale is called Brand X Foliage Cleaner. It is available through Southwest Plantscape Products in California (www.southwestplantscape.com). Their phone is 800-333-7977. It is a silicon-based product so it is very slippery. Its ability to penetrate is probably the key to its effectiveness because it gets into the tiny crevices that other sprays miss. I'm sure something similar is available locally.
Another idea is to spray with rubbing alcohol -- that will help break through the hard outer barrier of the scale and kill it. Mix 1 part alcohol with 5 parts water. Add a little liquid soap to help it spread.
Another good nontoxic spray is Hot Pepper Wax. Its main ingredient is hot cayenne pepper that overheats the plant pests. There is an information website for it at www.hotpepperwax.com.
Don't apply any of these sprays to plants in direct sun or in high temperatures.
Whitefly eggs are found on the undersides of plant leaves, where they are barely noticeable. If possible, take the infested plants outside and spray the undersides of the leaves with a moderately strong hose spray. Be thorough so as to get all of the eggs. In the process, most of the adult (winged) whiteflies will also fly off. That is why this should be done outside. The whiteflies can also be treated with Brand X or with soap and alcohol as described above.