Gall wasps are one of the most common lemon tree pests. The gall wasp creates galls in your lemon tree by laying eggs inside the branches in early fall. The galls are unsightly, but they are unlikely to kill a healthy tree. However, a significant infestation can weaken your lemon tree and stunt its growth. Since gall wasps do not live in a central hive, it's impossible to eliminate every wasp in the area. But, you can keep them away from your lemon tree.
Prune off the galls.The galls contain wasp eggs and must be removed before the eggs hatch in spring. The most effective way to do this is to simply trim away the section of branch that contains the gall.
Dispose of the galls correctly. Ideally, they should be burned. If you cannot do that, place the galls in a sealed, black plastic bag and leave it out in the sun for a few weeks. This will kill the eggs. Then toss the bag in the trash.
Deter wasps from your tree. Use a knife to poke several pen-sized holes in six plastic soda bottles. Then fill each bottle with six mothballs. Hang the bottles from your lemon tree with string in late summer. Any female wasps looking for a place to lay their eggs will look elsewhere.
Fertilize your lemon tree with an 8-8-8 fertilizer to encourage new growth. However, there is no need to over-fertilize. Apply the same amount as you usually do and make sure that the tree does not receive any more than four fertilizations per year.