Hi, and thank you for contacting Ask an Expert regarding your grapes my name is Seamus.  Even though grapes are not my expertise I will be doing my best to answer your questions.

I have an inkling as to what is happening to your vines, but I would like the opportunity to further investigate the issue.  Tomorrow evening I will be meeting with other colleagues and I will be inquiring at that time for more opinions and to verify my own before I respond back to you.

If I fail to receive any adequate answers I will on Tuesday continue to do research.  I want to be as though as U can so as not to give you any incorrect information.

With that you should here back from me by Wednesday at the latest.  Thank you for your patience.

Mr. and Mrs. Connelly,

Thank you for your patience as I further researched your grape plants situation.  After I spoke with Will, a Master Gardener colleague of mine, who has many grape plants and knows a few experts on the subject.  He gave me his opinion on the matter but asked me not to report anything back to you until he could confer with Ray Ethell.  Ray owns his own nursery, belongs to the Wine Growers Association, and is a major supplier of high quality, grafted grape plants to Pacific Northwest vineyards.

This is their email correspondence:

Will:   Ray,

A fellow Master Gardener came to me with a question he had received from a home gardener. There is not much information here but there are a few pictures. If you have time could you look at the three pictures and let me know if you have any ideas. I have 20 vines I got from you in 2012 and I have not seen this problem. I would suspect that the wind might have broken these canes off. I can think of no other reason she would be losing so many canes. The pic’s do not show any animal damage and there is no mention of animals in the text.

Is there any known problem with grapes that causes canes to fall off other than wind or animals?

 Ray:  Will,

This looks like wind damage at a time of rapid growth with shoots without some kind of support. This spring is a classic example of rapid growth because of the cool spring followed by a week of warm weather causing this rapid growth. This rain today may cause some more of this. The plants need some support for the new canes.

I hope this information sheds some light on your vine problem.  Should you need further assistance, have additional questions or comments you can either ask a new question and one of my colleagues will respond or if you prefer you may reply back to this message to continue corresponding with me.  Again, thank you for contacting Cooperative Extension Ask an Expert.