Appellation Cornell on Crown Galls

I've subscribed to the online newsletter from Cornell University called Appellation Cornell even before we began planting our vines. In this month's newsletter, I found a timely article written by Tim Martinson and Tom Burr that answers the question I Have Galls in my Vineyard: Should I Call my Nursery?.
This question could have been written by us because as we did our pruning back in April, we noticed that there was crown gall on some of the plants. As we focused on which plants had the crown gall, we realized that it was only the Auxerrois that seemed to have succumbed to this malady. We pulled out those vines affected with the crown gall and considered notifying our nursery.
The organism that causes the crown gall is a bacteria called Agrobacterium vitis.
What Tim Martinson and Tom Burr report in this article is that when a new, more sensitive testing method called magnetic capture hybridization (1000 times more sensitive in detecting the bacterium) was used, it was found that A. vitis is rather ubiquitous in the environment. Even if crown gall-free foundation plants could be generated, the chances for infection in the vineyard still remains a possibility.
Gall-formation is triggered mainly in damaged tissue in response to cold injury or in graft unions (where tissue is intentionally damaged and callus tissue forms at the union to bond the rootstock and scion together).

Here on the right, is a photo of our Auxerrois with crown gall formed at the graft union, which in our case is a tall-grafted vine. The bacteria forms at these sites after transferring an element of its DNA to the plant. During the spring, when the grapevine is actively growing and dividing, the DNA transferred to these cells from the bacterium gets expressed and causes the tissue to form galls instead of forming organized conductive tissues (e.g. Phloem, cambium, and xylem tissues) to repair the injury.
So the answer to this question is, "Your nursery is not to blame."
References:
1. Tim Martinson and Tom Burr, I Have Galls in my Vineyard: Should I Call my Nursery?, May, 2015.
2. Burr, T. and T. Martinson, 2015, Grape Crown Gall, Factsheet of the National Clean Plant Network – Grapes.