I've been having trouble with the rest of my grapes. The Concord and Fredonia all look like they have serious chlorosis, but the addition of iron hasn't helped.
I also have a Black Spanish and a Brilliant which are doing fine for 1 year old plants in this high pH soil I have to contend with. These two are cultivars bred for the area.
The amazing ones are the supermarket plants (planted from seeds from supermarket grapes). Those are all growing the way I expect grapes to grow. In fact, one of the grapes appeared to have died back in March, then re-sprouted at the base and is now approximately 5ft tall.
Have you tried an iron foliar or an all purpose foliar (that also has iron) such as this which is available in my Home Depots at least. All below are chelated minerals and iron
http://www.southernag.com/docs/labels_msds/chcitr.pdf
Iron foliar http://www.irrigation-mart.com/Documents/Chemicals/ironchelatedp.pdf (they have one chelated iron drench for high ph soil and one for low) (but all can be used as foliars) (think chelates!!! whether foliar or into the soil)
I have Ison’s black http://www.isons.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=IN&Product_Code=Potted_Muscadines and a few other muscadines climbing. The vines are so beautiful to see putting out tendrils and branching out