After receiving the DexNav update for your PokéNav Plus, you can go west from Oldale Town to Route 102.
In this area, you can catch Seedot (in Omega Ruby) or Lotad (in Alpha Sapphire), Zigzagoon, Poochyena, Surskit, Ralts, and Wurmple.
Explore the Route
Go southwest west and you will encounter a pokémon trainer. The first time a pokémon trainer sees you, he or she will challenge you to a pokémon battle. In this case, the trainer is Youngster Calvin, who has a Zigzagoon.
West from Youngster Calvin, you find Bug Catcher Rick, who has a Wurmple.
To the northwest, you encounter Youngster Allen, who has Poochyena and Taillow.
To the right of Allen, you find a couple of berry trees. Be sure to get the berries from each tree, then plant more in the soft soil.
Go west from the berry trees and you will encounter Lass Tiana. She has a Zigzagoon.
South of Tiana, you can find a Potion next to the tall grass.
Go west from Tiana and your neighbor will meet up with you. You will notice a few Beautifly flying past. Your neighbor will continue on to Petalburg City, where your Dad is the Gym Leader. Afterward your DexNav will detect the nearby Beautifly, adding them to your pokédex.
When you are ready, go west to reach Petalburg City.