The photo is not very distinct but it looks like there is more than just a single weed species there. Any broadleaved weed killer listed for lawns should work. My preferred product for this purpose is Bayer's All in One Lawn Weed and Crabgrass Killer. It is a liquid, comes in a ready to use spray or in concentrates (various sizes) that can be mixed and applied with a sprayer for broader coverage.

Is the Bayer product a pre emergent or post emergent?

It is a post emergent herbicide, which is what you need. Otherwise, you would need to pull or somehow remove all existing weeds before applying a pre-emergent.

In some climates (like mine) these two grow year round so relying on the Summer to kill them may not work. Even if it dies down, Chickweed will already have dropped a million seeds and the Glechoma will just be lying doggo.

Marc, where in the world are you? Since you are planning on spraying something in February you must be somewhere south. There are several plant poisons that can be sprayed to temporarily kill off those unwanted plants, but that also means spraying again and again.

The best way to keep unwanted plants (often called weeds) out of the lawn is to grow a good healthy lawn and that starts with the soil the grasses grow in.

What is that soils pH?

How much organic matter is in that soil?

How well does that soil drain?

How well does that soil retain moisture?

What kind of life is in that soil?

kimmq is kimmsr

I'm in north Alabama (where healthy crabgrass will take over pets, small children, and low flying planes). At the moment, I'm waiting on the soil temperature to come up closer to 50 degrees, so as to apply Scotts® Halts Crabgrass & Grassy Weed Preventer at the opportune time.

I completely agree with your statement about growing a healthy lawn, which is why I'm taking steps to prevent the crabgrass and eliminate existing weeds. Since I'm on step 1 (application of crabgrass preventer), I don't have the soil pH info, nor the organic matter content (yet). Drainage is fine.

That being the case, what would be the best approach to eliminating existing chickweed? I really haven't had much luck with big box herbicides. I haven't tried the Bayer brand, though the ones I've tried seem to hurt the weed's feelings for a few days and that's about it.

Chickweed is a prolific seeder and those seeds are spread about by birds. Most of the time when unwanted plants lie Chickweed are killed off any new growth is from seeds delivered by birds. so repeat spraying with those poisons is necessary unless you can find the source of the seeds and eliminate those plants as well.

I do not have personal experience with any of the common plant poisons but am told that any containing 2,4,D and Dicambra is effective at controlling existing Chickweed. Where Chickweed, I find hand pulling unwanted plants such as Chickweed, Purslane, Knotweed, Black Medic to be as effective, and less environmentally problematic, than spraying poisons.

kimmq is kimmsr