Dave Leonard (Consulting Arborist, Dave Leonard Tree Services, Lexington, KY) brought a fascinating gall sample to the Greater Cincinnati Diagnostic Walk-About last week. The woody galls were on hickory (Carya sp.) and sparked an informative diagnostic discussion among the participants.
Jim Chatfield and I were flummoxed several years ago with trying to identify woody galls on the main stem and branches of a large hickory tree growing in Secrest Arboretum, Wooster, OH. Had the tree been an oak, we may have suspected the woody branch galls were horned oak galls produced under the direction of gall-wasp, Callirhytis cornigera (Family Cynipidae). Of course, the wasp galls do not develop on the main stems of large trees.
The growths also resembled crown galls produced by the bacterium Agrobacterium tumefaciens. However, their multiple sites with locations high on the tree didn't fit well with that diagnosis. Unfortunately, we didn't send samples to our Clinic for a confirmation one way or the other.
However, a perusal of Sinclair and Lyon's Diseases of Trees and Shrubs (2nd edition) provided a possible diagnosis that does fit with both the appearance and locations of the woody galls. On page 148, the authors describe galls produced by a fungus belonging to the genus, Phomopsis.
Here are some quotes from that publication: "In the course of early studies of crown gall and other plant tumors during the 1920's and 1930's, many gall and tumor diseases were discovered that could not be attributed to known causal agents among bacteria, fungi, and insects. Many galls, being economically significant, were never satisfactorily diagnosed."
However, the authors go on to say, "Phomopsis species were first recognized as possible gall inducers in the 1930's." And, "The gall-inducing Phomopsis was originally detected when it grew from bits of internal gall tissue onto laboratory media …" More telling in terms of Koch's postulates, "The Phomopsis isolated from galls on Carya and Quercus was reported to cause galls when inoculated into wounded twigs of Viburnum, Jasminum, and Ligustrum, in addition to the original hosts."
The authors list a wide range of other possible hosts including red maple (Acer rubrum), sugar maple (A. saccharum), American elm (Ulmus americana), highbush blueberry (Vaccinium corymbosum), cranberry bush (Viburnum opulus), and Forsythia spp. Of course, finding woody galls that appear to "match" with images purported to show Phomopsis galls should not be the final diagnostic step.
You should do what Jim and I failed to do when trying to ID the galls on the hickory tree in Secrest Arboretum (do as we say, not as we do?): send samples to our OSU C. Wayne Ellett Plant and Pest Diagnostic Clinic: https://ppdc.osu.edu/
Here is a direct link to the instructions for sending woody ornamental plant samples:
Here is a direct link to the General Form that you must include with the sample:
There appear to be no treatments for suppressing Phomopsis galls other than possibly pruning them out of small trees and shrubs. However, that should not prevent you from sending samples to our Clinic. Learning the true source of the galls will guide your management plans and reinforce your message to a customer. A Clinic confirmation that they are Phomopsis galls will support telling your customer there is nothing you can do for their tree that will eliminate the galls. On the other hand, if the galls are being caused by something else, this knowledge can inform your management plans and likewise underpin your message to your customer.