Seedless concord are a heavy producer of juice grapes but they do not all ripen at the same time which takes more effort to pick them.reliance is a great tasting grape though does not yield like a seedless concord. Mars tastes ok and yields ok. If I was to cull one it would be due to flavor or production. In my situation that would be mars that comes up short. The fact seedless concord is not seedless sometimes may help make your decision.

Thanks Clark, I wish I would have done more research because now I think I may replace two of the three.

How about some suggestions on some varieties that do well in lower southeast mi. zone 6.

Preferably seedless.

I grow the above mentioned grapes and they all have their advantages. Seedless concord are prolific and highly disease resistant in this area. Keep in mind seedless concords are not seedless in Kansas where we live but in zone 6 they may be seedless. Red canadice is my favorite. Canadice are not overly disease resistant or heavy producers but the flavor is incredible. I think you would enjoy them.

For a white grape you might look at Marquis Seedless or Cayuga since they are a very good white in colder areas. Tickled Pink Grapes are said to contain seeds in some locations and I'm growing them anyway and will let you guys know an update when they start producing. Our weather in Kansas is harsh at times and it causes some seedless varieties to develop seeds. The mars grape has a nice flavor and is fine for juice but the Kansas weather makes their skin like leather. Red Canadice though still technically a slip skin has a very thin skin.

For your zone the European varieties aka Vitis vinifera such as perlette will always yield better flavored / textured grapes than the American varieties aka Vitis labrusca we can grow here. I love Vitis labrusca for juice and prefer that rich flavor over anything else. I still go to the super market and pick up some Vitis vinifera from time to time for fresh eating. If I was in zone 6 I would try some muscadine grapes aka Vitis rotundifolia.