seedless grapes with seeds?

Hi I have a Canadice seedless grape vine and a Stueben vine (like concord) planted side by side.
The first year I got grapes from the Canadice they were seedless as they should be. Then, we had 2 bad winters where both vines died right back to the ground. This year, I got about 6 clusters off the Canadice and some grapes had seeds. Some seeds were very small but some were normal size.
The local nursery says that it shouldn't happen but I think some cross pollination is going on or the Canadice is a plant grafted onto a base plant which does have seeds and after the die back I'm getting branches and grapes from the base plant.
Anyone know what's happening?
Tnx Wayne
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Are there any seeded grapes planted in the neighborhood within 300 feet of your seedless grapes? If so, that will affect the outcome. Some seedless grapes still have small soft seeds, but not like you described.
How old are the plants? I know of a flowering crab apple tree that flowered for the first 4 or 5 years, and then started bearing apples. They taste fantastic, but aren't supposed to be there at all.
Dwayne

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Most likely, The seeded grapes are from the rootstock. Any time you get die back, that is a distinct possibility.
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Wayne Jones wrote:

Some kinds of grapes are grafted but the kinds you have almost never are. Canadice almost could be grafted because that variety is very prone to a canker disease low on the trunk. Possibly grafting could help prevent that. I would think it would be very obvious if you were now getting grapes from a root stock. Canadice grapes have a unique taste (which I don't happen to like... I replaced mine with something better). If you tasted the Canadice grapes before the die down, do this year's grapes taste about the same or not? Should be a simple question to answer. If they taste like Canadice, I think you can expect the grapes to be seedless again in future seasons. Cross pollination could be the problem, though I don't believe I have ever heard of that causing trouble. I've been eating Venus grapes this week. They are considered to be seedless grapes that sometimes produce a few soft seeds. This year they all have seeds and some of the seeds are not soft either. We had a warmer than normal summer, by our northern standards, but I don't know why that would matter. Most people growing Venus grapes would live where it gets hotter than this every year. By the way, there absolutely, positively are no seeded grapes growing anywhere near my yard. If your vines sometimes die back to the ground, you should be doing what I am forced to do every year: Prune the vines in the fall, after the leaves fall off, and then lay them down flat on the ground. Use things like bricks and boards to keep them flat. You have to plan ahead for this by developing a trunk that is long enough to be flexible and emerges from the ground at an angle that allows it to lay down. A thick trunk growing straight up isn't going to bend down.
Steve, in the Adirondacks. (growing 4 or 5 kinds of seedless grapes where the winters get at least 30 below zero every year)
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Thanks for your comments. If I am getting grapes from the original rootstalk then I guess the plant is kaput no? I did find that originally the canadice grapes were very mild tasting but this year's tasted much like a concord. However, the grapes didn't all have seeds so it must be a cross pollination problem. However again ,you say you are getting seeds too so maybe it's the result of that hot summer we had. hard to come to a conclusion eh ;-)
I think I'll get rid of the steuben and see how the canadice turns out then. Wayne
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Wayne Jones wrote:

If you do get rid of the Steuben, that will open up space to plant a really good seedless variety such as Vanessa or Reliance.
Steve
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