I have this problem on both my lemon and lime trees. Both are in 500mm x 500mm pots and about three years old.
13 July 2014 11:30 PM
These nodules are galls produced by the citrus gall wasp. They occur when extremely small black wasps lay groups of eggs in young soft twigs etc. The larvae of the wasp develops and stimulates the plant to produce extra cells. These galls increase in size and become full sized by autumn. It is important to remove and burn the galls by the end of August because in September/October, the adult wasps emerge through the outside of the gall and because they are poor flyers, will reinfest the same tree.