One example of a successful protest tactic used by the United Farm Workers in the late 1960s was a boycott of

One example of a successful protest tactic used by the United Farm Workers in the late 1960s was a boycott of:

table grapes grown in the Delano fields.

Explanation:

By using "the Delano grape strike" as the most notable for the effective implementation and adaptation of boycotts, the United Farm Workers were able to forge the unprecedented partnership between the Filipino and Mexican farm workers which eventually unionized farm labor.  The result was the creation of the UFW labor union.  Through its singular and innovative efforts and examples, the UFW revolutionized the farm labor movement in America.