Exterior wood - treatment

[Jupiter01]

I've ordered in a custom sized capping for my featheredge infill as seen in the picture. The timber merchant has advised that the wood will no longer be treated as it's being cut from all directions. I will eventually give everything a coat of ronseal.
Q. do I need to so something first with this untreated capping?

 

[opps]

I'd be inclined to give it a coat of solvent based wood preservative first.

Just be aware that sawn timber and planed timber absorb finishes at different rates.