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.
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