Okay I just looked at the vine and here it goes. There is one cane or arm I think it is and it goes from older wood to younger thinner wood it is in the pic of where it splits into a Y shape and the top one is the younger one that is producing grape clusters all along the cane. Now the older and thicker wood has a young cane growing out of it that is about five or six feet long and it has some grape clusters and down along the older vine I left two buds per node and they have a few clusters of grapes. Older with young cane coming out Older with Grape cluster Young cane with grape clusters Top one is the younger cane, the bottom one is the older cordon.

I'll try. Only the top plant is large enough to perhaps bear any fruit this yr. Cut the smaller plant back severely and train the strongest shoot up a stake to try for fruit next yr. When that shoot reaches the top wire, pinch it back to get a shoot running in each direction. Those shoots, which grow this yr, will produce fruit next yr. So don't prune them off next winter. On the larger plant I cann't tell what is last yrs wood and what is older. Only last yrs wood will bear this yr. If you are going to get fruit this yr it will be on the shoot labeled B1. Cut off that bottom shoot going left. Also cut off the shoot just to the left of B1. It looks like older wood. Always cut off as much older wood as possible while leaving enough of last years wood to produce a crop. Now you are left with the B1 shoot that branches right and left. These canes are the one label C1 and above. If they are last yrs wood, they may fruit this yr. Cut off every side branch below C1. Keep one cane at C1 or higher going in each direction and see if they fruit. Each yr after this you will keep one cane going in each direction that grew the prior yr and cut off all other canes. This gives you a T shaped framework after pruning each yr. It's as simple as that. Your vines lack enough vigor to bear much fruit. They either need more water or more fertilizer, assuming they are getting enough light. The Fruitnut

TE: It won't hurt the plants but will knock out your harvest for 2013. And it won't solve your long term issue which is learning how to properly prune and doing it every year. Pruning grapes is easier than it sounds and something you will enjoy once you understand how it's done. If you instead try to regain control and correct this issue over two years instead of one, you won't miss a harvest completely. Next spring prune off as much of the old wood as possible while still leaving a few canes with this summers wood at the ends of the shoots. Then when you prune in spring 2014 you will be have lots of new growth and can prune properly. You will need to remove 80-90% of the canes as short as possible next spring in order to really turn things around.

I really can't tell from your photos, but offhand I'd guess powdery mildew. You can take some leaf loss from that especially this late in the season. http://extension.arizona.edu/yuma http://extension.arizona.edu/yuma-master-gardener Give them a call and find out when they have either a diagnostic clinic scheduled or if a plant pathologist is available for you to drop by. When you do visit, take a FRESH cutting of the affected vine IMMEDIATELY before you go in and SEAL it in a ziplock bag so disease/pest won't spread.