One Gall, Two Gall, Red Gall, Blue Gall
Written by: Luke Volbrecht, ISA Certified Arborist WI-1112A
Like something out of a children’s story book, galls come in many different shapes and sizes. Galls are also a common type of damage affecting tree leaves, needles, and/or twigs. Their size and shape can range from pointy to round and small or large. The color of a gall can be a simple brown, a bright red, or even blue. This leaf damage can be quite visible and easy to search for too!
Galls are often caused by very tiny Mites, Psyllids, or Wasps, often less than a few millimeters in size. Damage by mites or other insects occurs very early in spring, just as a young leaf or twig is developing. As the tissue continues to grow and expand, the gall also grows, and the affected areas can develop small bumps or larger, round, ball-like structures throughout the growing season. For some galls, the abnormal growth is a reaction to feeding damage, much like scar tissue. In other cases, the insect lays an egg between the leaf surfaces and a gall will form to become a home for that insect’s next generation. Despite the creepy crawly feeling this may create, most galls are nearly harmless to a tree’s health. Treatments are often not needed, and the galls are primarily a cosmetic issue.
One exception to this is the damage from Spruce Gall Adelgids. The spikey cone-like structures that form are occasionally found on spruce trees. These galls will cause a branch’s new twig growth to grow stunted and turn brown, then eventually dieback. When populations of this insect build-up, they can quickly disfigure the spruce’s appearance and reduce the aesthetic value of that tree. Treatments are available to help deter Spruce Gall Adelgid feeding, but most other galls do not require treatment.
If you find galls on your trees, do not fret! First, take a picture or two of the leaf/ twig and gall, then contact your Wachtel Certified Arborist to review and provide recommendations if needed. The pictures can sometimes help allow for a quick digital diagnosis and recommendation. Pictures can also be very helpful during late season identification as well. Good luck hunting for galls over summer and fall!