I don't know what it is, but I have to commend you on taking some excellent photos. Those are great.

Crabgrass!

Not crabgrass.

It's annual bluegrass, aka Poa annua.

I'm ignorant on grasses but I'm not totally convinced the two are the same species.

the one flowering is most likely Poa annua, the other without flowers looks like Poa pratensis, the ends of the blades are grown together like a canoe, when so fltten them with your finger, there a little funnelshaped gap between the tips, it is common in european lawn seed mixtures( and probably spread around the globe)

Looks like Poa annua to me, especially the one with flowers. The other one could be Poa pratensis. You can tell by the boat-shaped tips on the blades—if you press them flat, there’s a small gap in the middle. It’s pretty common in lawn seed mixes. I’ve dealt with Poa annua a lot, it usually shows up in early spring and dies off in the summer heat. Once it thins out, it’s easy to pull by hand.

Hahahahaha! Bot! Bot! Bot! Looks like it trained off of your post, @linaria_gw

Being a Lawn Care Specialist, That looks like annual bluegrass, commonly called Poa annua. The seed heads and the lighter green color compared to zoysia are good indicators.

For control right now, a selective post emergent labeled safe for zoysia such as products with foramsulfuron or trifloxysulfuron can help, but timing matters. These work best when the weed is actively growing and temperatures are moderate. Avoid spraying during extreme heat to prevent stress on your lawn.

That looks a lot like young rescuegrass or possibly annual ryegrass rather than a broadleaf weed. The clumping growth habit and narrow blades are the giveaway. The good news is zoysia is fairly tough, but grassy weeds are always trickier to selectively remove than broadleaf weeds.

If it’s only scattered patches like that, honestly the easiest and safest option is to dig the clumps out by hand before they seed. For chemical control in zoysia, products containing Celsius WG, Revolver, or Monument are commonly used for grassy weeds, but identification matters because some grassy weeds respond better than others. A spring pre-emergent like prodiamine or dithiopyr can also help prevent new germination next season without hurting established zoysia.

One thing I’d avoid is using generic “grass killer” sprays unless the label specifically says safe for zoysia lawns. You should just use plant identifier https://botanapp.com/ to check this plant faster next time - all that you need is mobile phone in your right hand.

Yeah, that's crabgrass creeping into a thin spot in your zoysia — pretty classic, I see this constantlyin the lawn. Easiest move right now: just pull those clumps out by hand while they're small, roots and all, takes two minutes. Come spring, before it warms up, lay down a pre-emergent like prodiamine so you're not fighting this same patch again next year.

Looks like nutgrass or wild garlic. Make sure whatever you use is safe for Zoysia's active growing season.

That does look like Poa Annua based on the leaf texture and growth pattern, but from the photos it could also be a mix — the broader blades in the third photo look a bit more like annual bluegrass going to seed, which behaves slightly differently and can be trickier to catch with just one treatment.

For Zoysia specifically, the good news is you have more options than people with Bermuda or St. Augustine. Zoysia handles certain selective herbicides pretty well when applied correctly.

For pre-emergent, Prodiamine or Pendimethalin applied in early fall before soil temps drop below 55°F is your best window for stopping Poa Annua before it germinates. Most people miss this timing and then wonder why their spring treatment didn't hold.

For post-emergent on an existing problem, Tenacity (Mesotrione) works on Poa Annua in Zoysia without causing damage — but you need two to three applications spaced about two to three weeks apart. One shot rarely does the job cleanly.

The bigger issue people overlook is that Poa Annua thrives when turf density is low. Even after you knock it back chemically, if your Zoysia isn't thick and healthy going into fall, the weed just comes right back the following season. Thin lawns are basically an open invitation. That's why weed control works best when it runs alongside a proper fertilization schedule — the two together close off the gaps weeds need to establish.

Hope that helps narrow it down. What does the root system look like when you pull one out?