Applied twice, one week apart, at recommended rate in late February on 1600sqft lawn. Located in Southern California. Temps ranged from 60degF to 70degF. Well established Poa showed signs of impact within 1 week of second application. No impact to St. Augustine. Some signs of impact to dwarf fescue. Fescue was already stressed due to fungus. Photo is of dying Poa (yellow grass in center) at week 4. Easily enough product for another 4-years of application if needed. Great value if Poa is an issue. Definitely recommend.

New Review (4 stars, 7/8 weeks after first application)
Kept my original 1 star review below as reference... About 6 weeks after my initial spray, long after I had given up on this product (and written the review below), I come home from work and noticed multiple brown patches developing where my quack was most fierce. It does seem to be working.. Every day the patches become more pronounced. I had spot sprayed pretty heavily so it does seem to also be rough on the immediate grass around the quack.. But this stuff does seem to work. If the quack I sprayed this fall is not around come late spring, I'll be logging in an changing my review to a 5... And buying more of it!!!! Another reviewer said "BE PATIENT"... He was right on the money.
I'd also really like to know if anyone has done general broadcast spray on an entire lawn and had success. Thanks!

Original Review below (1 star, about 4-5 weeks after first spray)

I don't like to give negative reviews, but I tried this product twice (with Southern Ag surfactant). On the second application, I had double the recommended concentration of Certainty (spot spraying only so wherever I sprayed got a HEALTHY dose of this mix). I don't see this product affecting the quack at all (as I hoped). More oddly, it didn't even seem to be working on more common broad-leaf weeds and thistle plants that were directly sprayed. I wanted it to work soooooooooo badly, but for whatever reason my bottle just is giving no results. Is it possible they made a bad batch of the stuff, as others have had such good results? Anyway, at nearly $100 per bottle, I just can't afford a second bottle to experiment.

Great product! A little expensive but worth the money. You only have to use a little amount and the container will last a long time.

Excellent product

The only product that selectively killed the weed in my grass.