Question
We were given a Meyer lemon tree for Christmas.  It stayed indoors until just recently.  While still inside I noticed a sticky coating on the leaves which also appeared on my hard wood floors around the tree.  It did not look healthy so I was hoping taking it outside over the summer would help.  Since it's been outside, it still has a sticky substance on the leaves, plus it is majorly attracting ants.  I also suspect it has aphids.  I don't want to spray it or do anything until I'm sure what the problem is.  I've surfed the web but haven't found any helpful websites about identifying and treating diseases on Meyer lemon trees.  Any ideas?

Answer
Hi Susan,

The problem is some sort of sucking insect (aphids, whitefly, scale insect, or mealybug.) All of these insects secrete as a waste product a sticky, sweet compound called "honeydew."  Since you see large numbers of ants, the ants may be "farming" aphids on your lemon tree.  Ants and aphids have formed a symbiotic relationship in which the ants derive food (honeydew) from the aphids.  

Once outside (if you have a relatively vigorous plant community), the natural predators usually take care of the sucking insects.  

Another common insect is the scale insect, the juveniles of which are mobile, small white crawlers.  Once they establish feeding sites (either on the stem or leaves), they form a hard, oval-to-round (~2.5 mm) shell.  The adults then remain their for the rest of their lives.

Examine your plant carefully for scale insects, aphids, and mealybugs (which appear as cottony masses usually at the juncture of the leaf petiole and stem).  Once the culprit is identified, contact your local garden center for control measures.  There are many organic (soap, alcohol) treatments available.  Removal of adult scale insects is very tedious, but they can be controlled.