You will need Strength, Waterfall and Surf
Go to the victory road side of Route 22. There'll be a lass beside a river, surf down he river and down the waterfall.
Surf south of the waterfall a little, hen Hop off. Beat a couple of trainers and a Strength Puzzle and Voila. I think the TM is Earthquake and I know the berries are Tanga berries. Hf