What ARE Those Fuzzy Lumpy Things on my Tree’s Leaves?
September 1, 2020
Learn about tree galls
Tree galls...creepy or cool? When you first encounter galls on your tree, it’s easy to panic. Galls can be quite dramatic looking and justifiably cause concern about your tree’s health. We get many phone calls and emails from worried homeowners about strange bumps and growths on tree leaves and branches.
While those fuzzy or lumpy bumps – called galls - can look like something out of a horror movie, they rarely cause significant enough damage to be concerned about. That said, stressed trees may need a little extra help if heavily affected, and certain gall-forming species can cause significant damage to commercial tree crops, such as pecans. So it’s good to know a little bit about galls and what causes them, and when it’s time to get help for your tree.
What are leaf galls?
Leaf galls are unusual looking growths caused by damage from insects and pathogens. Galls can be found on any part of a tree; including stems, leaves, roots and even flowers and fruit. The galls you’ve most likely noticed typically form on leaves and stems.
A gall forms when insects – such as tiny wasps, mites, gnats or aphids– deposit their eggs into the leaf tissue, or other tissue on the tree. The egg implantation wounds the leaf tissue, and then the hormonal response from the tree, as the larvae grows, forms a gall around the area as type of scar tissue. Galls can also be caused by the saliva of insects as they feed on the plant tissue, or excrete other substances. Certain nematodes, fungi, and bacteria can also cause gall formation.
In most cases, the eggs hatch inside of the gall and the larvae feed until they are ready to mature and emerge. Oftentimes, by the time you notice the gall, the larvae have already emerged and moved on.
Typically, gall-forming insect species each prefer a certain species of host tree, or related group of tree species, in which to deposit their eggs. For example, a species that lays its eggs in your pecan tree typically won’t also use your oak tree as a host, and vice versa. Some will only lay eggs in red oaks, but not white oaks.
Arborist Getth Nelson:
“Most people are very intrigued by the presence of gall insects. Galls very rarely cause significant enough damage to warrant the use of insecticides. When chemical controls are necessary, efforts will generally be targeted towards next year’s growth when the insects that cause the galls are laying their eggs.”
Recently, we were called out to a property near Crowley, Texas to an isolated case of galls. The foliage on some leaves of the Chinquapin Oak were severely distorted, and some leaves were completely covered on the underside in fuzzy, beige galls that looked like dirty cotton.
There are many types of galls and gall-forming species common to the DFW area tree species. Most are caused by tiny or microscopic wasps and flies, such as Andricus quercuslanigera (woolly gall), Disholcaspis cinerosa (mealy oak gall), Amphibolips confluenta (apple oak gall), Neuroterus flocossus (oak flake gall), just to name a few.
Is treatment for galls necessary?
Normally, by the time you notice galls on your trees, the insects that caused them are long gone. Therefore, chemical treatment at that point in time would be non-effective.
Most of the damage caused by galls is cosmetic and will not cause too much damage to your tree. But, if your tree is already weak or stressed due to other factors, an infestation of galls can cause further stress and decline.
As always, keeping your trees healthy through yearly inspections, preventative care, and fertilization from our SEASONS program, is the best prevention against insect attacks.
If your tree has galls and you are concerned about its health, call in an experienced professional arborist for a professional evaluation. We can help you decide what the next steps should be to help return your tree to optimal health.