Citrus plants are very attractive to a number of insect problems - sucking insects like various scale, whiteflies and aphids are most common and all will produce that syrupy-like substance, known as honeydew. Is your plant indoors or out? If outside, just hosing it down periodically with a sharp stream of water should help, as moist, humid environments are not to these guys liking and the water does have an ability to dislodge them as well. Indoors, I would limit my spraying to something like Neem oil rather than a commercial synthetic pesticide that might carry a much higher degree of toxicity to you. And I'd also think twice about what I was spraying if I intended to eat the fruit. Neem is quite safe.

FWIW, I was just in SoCal and had the opportunity to examine several citrus trees in a client's garden - they were all heavily infested with scale, older leaves quite covered with sooty mold and yet they were still producing lots of lemons and limes.

Sorry, I forgot to include the following link. It includes a wealth of info on citrus and their problems.

Here is a link that might be useful: citrus resources

I also have a two lemon trees that are almost three years old . Still no fruit. Does anyone know when to expect fruit to bear in South Texas?

Mine bore fruit from the beginning. At first the fruit 1st appeared in Jan/feb/march and ended in Nov/Dec. Now it looks like it will bear fruit year round. I have some bigger than golf balls, some brand new babies and lots of flowers. I use the gradular citrus fertilizer about every three months. I usually buy shultz, but bought the miracle grow citrus shake and feed last time (at Walmart) and have lots of blooms. Mine is a meyers Tree, not dwarf and is potted. I live near san antonio in New Braunfels. You have my email now if you want to reach me. anntl@satx.rr.com