Are those aphids? In orchards, it is not recommended to use sevin for aphids. It kills too many aphid predators. Not sure if that is a concern for grapes.
Admire Pro provides excellent control of aphids in apples. It is used on grapes for control of phylloxera, leafhoppers, and asian lady beetle. Malathion is also commonly used to control aphids in other crops, and is labeled for use on grapes. Unfortunately, the pest control reference I use doesn't talk about aphids in grapes.
There are various formulations for organically controlling aphids in grapes, or any other crop. Most of them are mixtures of water and soap, with other amendments as desired, such as cooking oil. I have also seen references to adding rubbing alcohol, hot pepper and even peroxide. A standard recommendation coming from USDA is as follows:
liquid dish soap - 1 teaspoon + on cup of vegetable oil (shake vigorously)+ I quart of water,
You can also purchase and release predators, such as lady bugs, but this would probably be more practical for a larger vineyard rather than just one vine. You could also purchase Neem oil, or Safer brand insecticidal soap.