I have recently planted 10 merlot vines and the leaves on some of the vines are stunted in growth and are curled. I see no insects or fungus and I have been watering daily to establish the vines. They are in full sun and otherwise look healthy.
It's tough to say really. There are a bunch of things to consider. However, in a stunning spasm of conclusion-jumping, I'm going to say that the stunting and cupped leaves combined with otherwise healthy looking plants bring to mind a nutrient deficiency. (Even though grapes require very little by way of nutrient application for the first year or two, it's a possibility). I'm thinking particularly of boron deficiency which shows up as short internodes and deformation of lower leaves. If you are in Southern California, the chance of that is a little less likely since irrigation water (both municipal and well water) in that area tend to provide enough boron to satisfy grape requirements for that element. Where you might run into trouble is a particularly sandy soil.
On the other hand, if you're up in Central or Northern California, that possibility becomes more plausible since boron is more likely to be low in the water and/or soil in those areas.
Is it a boron deficiency for sure? Heck, I don't know. That's a complete shoot from the hip response. To know for sure if nutrient deficiency (or excess) is part of the problem, petiole analysis should be done. That would just be a starting point. If nutrients don't turn up anything, look to other possibilities. Another good thing to think about is herbicide drift.
Back to petioles. Ideally you would collect 75 to 100 petioles next spring and submit them to a lab for nutrient analysis. If that isn't feasible, fewer petioles would be okay but try to get at least 30. Be sure to take them opposite of flower clusters. Timing is also very important since interpretation keys for grape nutrition are based specifically on nutrient levels during bloom; the closer to full bloom the better. Outside of that time window and doing petiole analysis is like giving a dead man an enema. It won't hurt, but it sure won't do any good. Don't send them in a plastic bag. That holds in moisture and the petioles rot on the way to the lab.