There are many different ways to catch Pokémon in Pokémon Brilliant Diamond and Shining Pearl, and one of them is by slathering honey on honey trees. Their gold leaves can recognize these. You will have to defeat Team Galactic in the Floaroma Meadows before gaining access to this.
This is also where you can get more honey in Pokémon Brilliant Diamond and Shining Pearl. The man you saved from Team Galactic will give you some honey for free and then sell it to you for 100 Pokémon Dollars. The other way to get honey is to have a Pokémon with the Honey Gather ability at your party.
Related: How to get Munchlax and Snorlax in Pokémon Brilliant Diamond and Shining Pearl
In Pokémon Brilliant Diamond and Shining Pearl, this Pokémon will be Combee. It can have the Honey Gather ability as one of its two abilities. This ability allows Combee to pick up honey at the end of a battle as long as it is not holding a held item already.
Slathering honey on honey trees is the only way to catch certain Pokémon, so it is worth it to do so if you want to complete your Pokédex. Fortunately, honey is quite cheap and easy to come by.
For more information on Pokémon, check out How to make a Secret Grand Underground Base in Pokémon Brilliant Diamond and Shining Pearl and Where to find the Quick Claw in Pokémon Brilliant Diamond and Shining Pearl on Pro Game Guides.