By Bud Franklin

Excerpted from January 2012 Tree Tips Newsletter

Galls are growths on a plant that are caused by an external pest, i.e. insect, bacteria, fungi, virus, parasite or nematode. They can appear on any part of the plant-leaf, flower, twig, branch, trunk or root.  They can range in size from hardly visible to quite large.

These abnormal growths are caused by an interaction between the host plants meristematic tissue (that tissue responsible for cell division) and the pest organism.  For instance, in the case of galls caused by wasps the larvae inject the meristematic tissue with a chemical that initiates the growth.  The larvae then has both shelter and nourishment during its development stage.

Surprisingly, galls are rarely  lethal to a plant.  They are, however, very unattractive and can cause an inherent weakness in the affected plant part.  Once they have been initiated they will not go away unless of course they are on a leaf or twig which eventually drops. The only way to prevent a gall from forming is to eliminate the pest organism prior to it’s having the opportunity to initiate the process.  In my experience, most ornamental tree galls are caused by insects which can be controlled with Acecap. Of course this must be applied prior to infestation so timing can be an issue.  Fortunately, Acecap is a season long systemic so if you are aware of gall formation in prior season an early spring application should be effective.

Leaf Gall

Root Gall

Trunk Gall

About the Author

Bud Franklin

I am a horticulturist with a B.S. in Horticulture from Colorado State University. I have been in the nursery business my entire life and currently reside in Arizona. My philosophy is to provide practical solutions to horticultural problems. Although I specialize in trees I have experience and training in all areas of urban horticulture including plant material, soil chemistry, pest control, plant propagation, irrigation and landscape management and installation.

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