I doubt fertilizer is your problem. I don't fertilizer at all with chemicals and things still grow. Be sure they are getting some water and otherwise let them be.

Hi Poolecw,
I planted 1 dixie and 2 carlos this spring in my yard as well. My carlos are still growing like mad, but my dixie has had mimimal growth throughout this entire season. I may relocate the dixie but the Carlos are doing just fine. I believe that they will slow down when it gets cool because they thrive in hot weather. I also have 2 concord grapes that are still growing rapidly and I had cut them both down early this spring to the ground because they had contracted a fungal disease last year. Now they are about 3 feet and still climbing. I will include pics when I get home to upload so you can compare with yours. Also, I agree with cckw, please dont over fertilize your grape plants, they will do well with litte to none. I gave mine a touch of fish emulsion and a little horse manure mixed with finished compost and that was it. I did this, 2 weeks after planting. They are very healthy and thriving so there is no need to continually fertilize. They will make it on their own. I am more focused on keeping them diseased and bug free. Good luck now.

ahgrower-

Its interesting to hear about your Carlos and Concords. The one Carlos that I planted this spring has been the slowest growing vine of the entire bunch. It hasn't quiet reached my top wire yet, while my Summits have not only reached the top wire, but have arms (four arms) that are now about two feet in length.

My Concords were the earliest to start growing and have arms about 3 ft in length.

But all of them have seemed to stop getting any length.

As for fertilizing them, I have been following the directions from Ison's Nursery.

Here's a picture of one of my Summit vines (female). The leaves on the Summit vines are HUGE! They are literally larger than a stretched out hand.

If you think to late to use 10-10-10 I would start using miracle grow that last 7 days each time apply use that keep vegetative growth the rest this season.
I'll use miracle grow if plant has good looking foliage just planted are late in season you come off MG sooner than can 10-10-10 I mix a gallon and use half on leaves some to water plant.

Your Summit looks great. Day lengths are getting shorter now, so expect a slowdown. Don't use too much ferts now- it can delay dormancy so they might end up with freeze damage