The image is a bit fuzzy but I think I see bumps on the bark. That would be citrus scale, an insect that grows a shell on the outside of it's skin as protection as it sucks the fluids from your tree. You can scrape off the sucking scales using a stiff tooth brush and soapy water or spray with Neem oil or horticultural oil to control them. Most scale begins when trees are brought indoors for the winter. Keep the foliage and trunk clean with soapy water and a good rinse to keep this insect under control. The scale will return after a first scrubbing so you will need to repeat several times. You may want to check on pesticide sprays made to control scale but be sure to follow the directions on the label. Neem oil is a less toxic product that commercial sprays but can also be less effective. Keep growing, Marianne Binetti