I'm not an expert, but I think this is fairly typical. Unless any of that wood is actively rotting (which would indicate a larger moisture issue that needs to be addressed), using old ugly boards to stabilize and level cabinets and countertops would seem to me like the appropriate approach during installation.

It looks like this was a remodel? If so, they definitely wouldn't have bothered to make anything look pretty if it's going to be hidden behind cabinets.

In other words - it's probably not as bad as it looks. If it ain't broke, don't fix it.

The photo does not show any signs of obvious rot. Maybe add a moisture barrier underlayment before completing the floating flooring, the install your new cabinets.

This is some minor water staining in an unseen area that's been around for a long time. Ain't nobody used that color green in 50 years.

_maybe _ there is a bit of.rotnon the bottom right wall but can't tell from this.

Are you just planning on putting a dishwasher back in the hole ? What's your goal? Because this is fine and honestly I wouldn't do any of what you are thinking unless part of a much bigger project

Pull up everything rotting and replace. Not fun but might as well do it right.

My house looks like this. I laid flooring not new cabinets. The builders laid flooring under the cabinets. I used some off cuts to fill the gap to let the dishwasher be level.

Mine basically looks like that behind the dishwasher as well ,70s house ! I love finding stuff like that.

Not the rot but the old paint and flooring

That bottom layer of wood, likely your subflooring, looks pretty solid.

That thin layer on top of it might be vintage linoleum, which can contain asbestos.

It's not doing much harm under the other layers of flooring, but be careful if you're determined to remove it, and consider professional help.

Otherwise, it's an area that will be hidden under the new dishwasher, and whatever other cabinets you fill the rest of the under-cabinet space with.

All you really have to worry about is making sure the dishwasher has a relatively level surface to rest its adjustable feet on.

Since you have the area exposed, you might also consider replacing the water stained drywall at the bottom. It might help make the kitchen smell less musty.

Or not. Again, it will be hidden.

Back in the day, kitchens were one of two colors; harvest gold and avocado green. Looks like yours used to be avocado green, congrats.

Looks like that wood panel on the left expired on 05-03-0941. Thats at least 1085 years of spoil. Does it smell rotten?

Pour a can of anti-fungus liquid on these boards, cover with a piece of linoleum or some waterproof rug, install your dishwasher, and leave further remodeling to your grandchildren.

Doesn’t look too bad!! If you can check underneath if there’s a crawlspace or something that’s where you could really find damage. You’d want to look for water damage to floor joists or mold growth. Doesn’t look like there will be any but always good to do a thorough check.