If the berry seller in join avenues rank is 10. Even if it is ,the only stat reducing berries are spec A ,spec D ,and speed. The berries also reduce 10 Evs per use. You would be better off training a new Pokemon unless you can get your hands on more stat reducing berries. Although you could also get a rank 10 grooming shop to reduce Evs to 0 but if your friendly with your Pokemon, they will refuse to groom it. Either way it's could be expensive.