Orange, Aloe and Lemon plants have black marking.
Client has an orange, lemon and aloe plant growing indoors. Plants are approximately 5' tall and about 6 years old. They are kept in a sunroom. Noticed problem 2 months ago. Has not had problem in the past. On the stem of each of these plants is a tiny black knot. Pictures attached are of the orange tree.
This appears to be one of the scale insects, perhaps a lecanium or oysterscale scale. You can get a better diagnosis by submitting a sample to the Michigan State University Diagnostic laboratory.
You can try peeling the scales off with a paring knife blade, and destroying them. Keep an eye for more over the next few months. There are several chemical options if this does not work.