Understanding Tree Galls

Posted on: 18 March 2020

You may have noticed an odd growth on a twig or leaf surface. It may have been smooth or fuzzy, lumpy or rounded. These growths are typically caused by galls, which are the result of an insect injecting a chemical compound into the tree to cause the fleshy growth. Why? Usually, it's a place to lay eggs. The gall will protect and the extra tissue will feed the young. The following guide can help you know when to ignore a gall and when to act.

Should You Remove Galls?

Although they can be unattractive, galls are usually harmless. Leaf galls will drop off at the end of the season, whereas those on twigs and trunks may remain but will no longer host any insects. There is generally no reason to remove a gall since it's growth typically doesn't harm the tree nor does it reduce the chances of future galls. You can prune out affected branches if they bother you, but you must avoid over pruning that would stress the tree.

Can Galls Kill a Tree?

Typically, a tree can survive with barely any ill health effects, even if it is covered in galls. The one exception is if girdling occurs. This problem typically affects branches of susceptible trees. Galls encircle a smaller branch, which prevents nutrient flow, causing the branch to die. Branch girdling isn't deadly, but occasionally galls can encircle a trunk and cause the same issue, which kills the tree. This is more likely to occur in younger trees with narrower trunks.

Are All Trees Susceptible To Galls?

Some trees are more prone to galls than others. For example, there are more gall-forming insects on oaks than on any other tree species. Maples are also prone to galls, which can help give the tree trunk it's well known knobby appearance. Other trees, like most conifers, red buds, and yews, are less likely to harbor gall-forming insects. Your nursery or tree service can help you find trees in your area less likely to develop galls.

How Can Galls Be Prevented?

Some galls, like crown galls, come from the soil, which can be infested with the gall-forming insects. Raking up leaf litter each year ensures it doesn't harbor the pest. Wrapping young tree trunks during winter may also help because it prevents thin, young bark from cracking. Many gall forming insects use these cracks to lay eggs and form galls. In severe cases, there may be a specific pesticide available to kill off the insects before they can lay eggs in your tree.

For more information about galls, contact a tree removal service near you.