The lemon tree is a cold-sensitive citrus tree, with a tolerance down to only 30 to 40 degrees F. As citrus trees, they are vulnerable to a wide range of pests and diseases. To keep the tree healthy, gardeners must meet the needs of the tree for growing, and then monitor the tree for signs of pests.
Lemon trees require full sun, quick-draining soil and consistent watering to survive. They fail in standing water and with frost. A failing lemon tree is more likely to fall prey to problems.
Galls are large, lumpy growths on the trunks and branches of a lemon tree. These galls are actually nesting places, where gall wasps have laid their eggs for spring hatching.
According to an ABC fact sheet, the gall wasp attacks all varieties of citrus trees and causes reduced blooming and fruiting. Trees that have gall wasps may experience severe dieback, especially if they're already weakened through lack of care.
The only way to get rid of galls is to use a sharp knife and cut them from the tree's wood. According to Global Garden, the galls should be burned, to kill the wasps and prevent propagation of the pests.
Spray the trees that had galls with insecticide to eliminate the wasps that laid the eggs. Then increase your care for the tree as it heals from its wounds. Increase your waterings to maintain soil moisture, and consider feeding the tree with a dose of 10-10-10 fertilizer to support its needs.