While I can’t definitively identify the weed from these photos, the fact that Weed B Gon had no effect points directly to a grassy weed. Products like Weed B Gon only target broadleaf weeds, leaving grassy species like quackgrass or nimblewill untouched.

Unfortunately, homeowner options for selectively killing perennial grassy weeds without harming the surrounding lawn are minimal. The most reliable fix is patch renovation: spot-treat the area (including a few inches past the edge of the patch) with a non-selective herbicide, then reseed or sod once it dies off.

If you prefer not to use glyphosate, your best alternatives are:

Hand Digging: Dig up small patches thoroughly and reseed, though surviving underground roots can cause it to sprout back.

Hiring a Professional: Licensed lawn care providers have access to specialized selective herbicides not sold over the counter.

So, in practical terms: if this is spreading in patches or by creeping stems/rhizomes, there usually isn’t a good over-the-counter “spray and save the lawn” product for it . The best remedy is often patch renovation rather than whole-lawn treatment.

If you can share a close-up photo of the leaf blades or seedheads, I can help narrow down the exact species.

Note: Herbicide information is for general guidance. Always check product labels and follow local regulations before applying chemical controls.

Below are hyperlinks to ISU Extension and Outreach materials directly related to your question.

How do I control perennial grassy weeds in the lawn?

How to Create a Pollinator Lawn

How to Manage Perennial Grassy Weeds in the Garden and Lawn

How to Manage Perennial Broadleaf Weeds in the Garden and Lawn

This close-up appears to be Nimblewill (Muhlenbergia schreberi), a fine-textured perennial grass.

IDENTIFYING FEATURES VISIBLE: 

Short, Flat Blades: The leaves are short (1 to 2 inches long), flat, narrow, and taper to a point, growing at distinct right angles to the stem.

Wiry, Branching Stems: The stems are thin, tough, and sprawling, creating a dense, tangled, mat-forming patch in cool-season turf.

KEY CHARACTERISTICS & CONTROL NOTE: 

Nimblewill is a warm-season perennial grass that spreads by creeping stolons (above-ground runners) and seeds. It turns brown/straw-colored early in autumn and stays dormant through early spring, often leaving bare-looking brown patches in Midwestern lawns during cool weather.

Because it is a perennial grassy weed (rather than a broadleaf or annual grass), standard over-the-counter weed killers won't touch it. For cool-season lawns (like Kentucky bluegrass or tall fescue), selective post-emergent options available to homeowners are very limited (such as herbicides containing Mesotrione / Tenacity), or, as discussed above, small patches can be spot-treated with glyphosate and reseeded.

Here is a ISU Extension & Outreach informational bulletin specifically on Nimblewill. 

https://yardandgarden.extension.iastate.edu/how-to/how-control-nimblewill-lawns