Question
I have had this lemon tree for about 3 years and it has fine but I have moved it inside for the winter and have noticed a sticky substance on the leaves, stems, branches, etc. No evidence of bugs but on the underside of the leaves are small brown hollow things(?) the leaves are falling off now, I have wiped the entire plant down (leaves, everything) with soapy water but after a week or so the stickiness is back? Any ideas? Thanks in advance..

Answer
Hi Vera...You did the right thing with the soapy water.  
The feeding of sucking insects such as aphids and thrips cause leaf curl on citrus. Aphid are small green or yellowish green insects. Their presence causes leaves to curl and yellow. They also secrete a clear sticky substance called "honeydew" which creates a varnish-like appearance on leaves.

I use only safe non-poisonous remedy, such as Neem Spray, organic, absorbs into the leaf so it cant wash off.  RE apply only when there is a problem with the new growth.  If you cant find Neem use an insecticidal spray that you can get almost anywhere.  These products kill the good bugs as well, that is why I prefer neem that kills nothing just alters the taste of their favorite leaves and makes them bitter, allowing the beneficials to eat the bad bugs.  kathy