I found that picture online and it was identified as Creeping Buttercup 'ranunculus repens'.

But when i search other pictures of Creeping Buttercup the leaves look thinner and the plant doesn't seem to be growing from a central root like this one.

 

Thats creeping Buttercup, the other is tall Buttercup.

Was looking up Buttercups to see if its as massive as it is here. Our dairy cow fields are yellow with blooms. Extension suggests the 2 4 d herbicide which is what the Speedzone is.

If its a small area or isolated plants, dig them up. The seeds can stay viable for 20 years so farmers riding over the plants are just replanting.

 

http://www.kingcounty.gov/environme...ment/animalsAndPlants/noxious-weeds/weed-identification/creeping-buttercup.aspx

Sure looks like the picture. This reference suggests a product containing MCPA. Repeat treatments usually needed. Lesco Eliminate contains mainly MCPA.

Speedzone is mainly Trimec plus carfentrazone. No MCPA. Its on the label but I doubt that the carfentrazone adds much, fast acting, but it attacks mostly young annual weeds.

 

I found out its not the Ranunculus repens (Creeping Buttercup) I thought it was, it is Ranunculus bulbosus (Bulbous Buttercup) the roots don't have runners, each plant has a single root like this.

http://en.wikipedia.org/wiki/Ranunculus_bulbosus (Bulbous Buttercup)
http://www.ct-botanical-society.org/galleries/ranunculusbulb.html (Bulbous Buttercup)

Bulbous Buttercup is not listed on the Speedzone label, but Creeping Buttercup is.

Any ideas on control, without harming turfgrass?