Answer: Newly planted grape vines (and other woody plants too) would need regular observation and care while becoming rooted and established during the first year or two.
The first few weeks are critical, especially if you start with a bare root plant. Bare root plants are better planted in very early spring just as soon as the soil can be worked (not frozen, not too muddy.) Container grown plants are also best planted as early as possible while the weather is still cool and relatively damp so rooting is facilitated and there is little heat stress on the minimal root system.
This past spring was very dry, so I suspect watering may have been a problem. Watering on a regular basis (as needed to supplement rain) is the most important thing to do. You would need to keep the soil evenly moist like a damp sponge, not sopping wet/saturated and not dried out. Using an organic mulch several inches deep in a flat layer over the root zone can also help keep the soil moist during dry spells.
It is also possible that a foliage disease caused it to defoliate. Most grapes require a routine spray program to stay healthy. Your local county extension should be able to tell you what is most important to spray for in your local area and when to do it, based on the prevalence of pests/diseases, the variety you are growing, and the weather each year. Be sure to clean up and remove any fallen foliage or trimmings.
You can check if it is still alive by scraping the bark with your fingernail; if there is a layer of green inside and the stems seem pliable and firm, it may still grow for you. If it is brittle and snaps in your hand, dried out and discolored, then it is probably dead. Trim off the dead bits beginning at the tips and work your way down the plant. Check for signs of sprouting as you move lower on the vine. It is possible it may have died back nearly to the ground, but still be alive and able to recover.
I hope this helps.
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