Vintners and growers may go their separate ways.

At stake in balloting starting this week is the future of Winegrowers of California, which united the two groups to enhance wine promotion. Vintners and growers vote separately; unless both approve the 2-year-old program, it will die June 30. The program assesses growers and vintners to raise a promotional budget--$20 million so far. But the marriage has not been happy, and the prestigious Napa Valley Vintners Assn. has strongly attacked the joint effort.