Do lemon trees grow suckers in the tops of the tree?
A fast growing vertical growth that originates from the trees trunk or branches are called Watersprouts.
A Watersprout growth can occur from weather or other damage to the tree; if the tree had been left unpruned for years, then was pruned, you may see this rapid growth.
The tend to grow vertically and can block light and circulation to the tree.
Left in place they can reduce the fruit quality and can be weak areas of the tree that may break and split easily.
Prune these branches as soon as they appear and use good pruning practices--clean tools, clip branches close to the truck.
Spring is the best time to remove these, but they may appear throughout the growing season.