On the second vine, there were more bunches of grapes, but they were ALL tiny, and so also disappointing. Tests are fairly expensive, and past the NPK and ph, they charge $5.00 for each additional element. Although there are about 20 reasons why these symptoms show on leaves, I think the most common reason for yellowish leaves on a grape vine, is Magnesium (Mg) deficiency. I sent you a brief note a few days ago with one specific question. I grow grapes to improve the appearance of our home, and am trying it to grow alongside up a pipe onto a balcony, and another grapevine over an arch fronting our patio (in a sunny location at the corner of our vegetable patch.).