The KBG probably won't choke out the fescue, but it will fill in bare spots. However, KBG spreads via rhizomes rather than stolons. Rhizomes should be below ground. You may want to take some of the weedy grass (including some roots) to your extension service to your extension service to get an accurate ID. I've seen blades of grass from the same plant get identified as two different grasses from pictures. It can be very difficult to ID grass from pictures. Many grass seed mixes have fescue and KBG in them. I think some types of fescue may mix better with KBG, but K31 grows much faster and has much wider blades, so I think a mixture of KBG and K31 fescue tends to look somewhat patchy. Where in WA are you? You may be better off seeding in the fall. It may not matter as much if you're in the Seattle area, since it rains so often there, but if you're inland where it gets hot and dry in the summer, a fall seeding will give the grass more time to establish before the hot dry weather hits.

This area of the lawn is composed of 100% of the Tif-type grass. The scalping is more evident. All of the pictures were taken yesterday after I mowed. Due to recent rain I had to remove 40 - 50% of the blade or raise the deck height.

I have these in my yard, they seem to be perennials. Amenable to being mowed, digging out the taproot is needed to remove. Mowing often enough so that new seeds are not formed/dropped will stop the spread of new plants, and this one does bloom again quickly after being mowed. Your post does not include your location but your "lawn" looks similar to those in my area. The "weeds" provide better ground coverage than the vine-like grasses that constitute a lawn in this area like Bermuda, St. Augustine, torpedo, bahiagrass, centipede. If your interest lies merely in having some kind of soft greenery instead of bare ground on which to walk and play, there is no need to be concerned about the non-grass plants within the mowed areas. There is a lawn forum here if it is your desire to try to cultivate a monoculture of grass.

That's not nutsedge, so don't spend any money on anything yet. Nutsedge is deeper green, shiny blades, ribbed blades, and has a triangular stalk. Also at that height it would have developed seed heads by now. Do you have any pictures where the weed has put up a seed head? The bermuda is too long, but it could be thin because of the weird weather we're getting. There's a lawn or two in San Antonio that are v e r y slow to awaken this spring. It has more to do with how it was treated last fall and the really cold weather (12 degrees in Austin) we had. My St Augustine died back and did not return in some spots. Now it is horse herb in those spots. How did you water it last fall and have you been watering so far this year? How often and for how long do you water? I watered my south facing slope for the first time (Bandera location) this week. With this ultra arid air we've had for a week, and no rain, I'm about to water the front.