Question
When my family was in vacation in Florida this past summer, I brought home a baby lemon tree (We live in California). It is in a pot, and has been indoors all through winter and late fall. The tree was doing just fine, until some sort of bug attacked it. There are small yellowish-white to brown bumps all on the branches, starting from the very bottom of the trunk (eggs?)--they are easy to scrape off without damaging the plant, and web-like fuzz also on the stems and trunk (especially right near the soil) and on a few leaves. There are tiny bugs crawling in the soil. The plant has stopped growing since the infestation. What are the bugs and how do I kill them?

Answer
Hi Julia,

The small bumps are scale insects, a very common insect pest in houseplants.  The fuzz may be a fungus that has developed on the organic rich soil.  The small insects in the soil are most likely fungus gnats.  The fuzz on the lower leaves may be the result of spider mites or could actually be juvenile scale insects.  These are very similar to mealy bugs as juveniles.  The adult scale insects are difficult to remove, but may be removed by using a mild soap and an old toothbrush.  The juveniles can be controlled by applying directly 70% rubbing alcohol with a cotton swab.  

When that has been done, place your plant outdoors and the natural predators will control the scale insect populations.  Watering the plant too frequently will allow the fungus gnat populations to thrive, depriving the plant of valuable nutrients, and in heavy infestations, significant root damage can result from the larvae.  Reduce your watering schedule, and water only when the surface of the soil is dry to a depth of one knuckle (~2 cm.).  These fungus gnats can live only in the upper parts of the soil, and if that layer is allowed to dry thoroughly, the fungus gnats will die out.