Deck maintenance

Recently purchased a 1800 psi electric power washer and cleaned 1000 sq ft pine deck after 5 years of neglect with watewr only.
I was motivated by an astronomical bid from a local contractor and decided to invest $170 to determine if I could do it myself instead.
Power washer worked like a charm, removing grime and mildew in no time at all. Property is located in Blue Ridge section of North Carolina and winters can be harsh coupled with the fact I am surrounded by trees (keeps it cool but very little sun).
Now that I own the power washer, I intend to keep after the deck more diligently.
My question is- If I keep after the deck with the power washer regularly do I need to apply a wood preservative? The deck is 5 years old.
Would appreciate suggestions from those more knowledgeable. Thanks

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