"Certainty" by Monsanto claims to kill it without killing Kentucky bluegrass. I started this new post because quackgrass is a huge problem with no good solution, and it seems nobody else on this site is aware of it. (if you try & it works, you owe me a six-pack) Check Monsanto's website for how & when to use it. LESCO sells it. It came on the market late last fall, so little is known in field trials. Basically -- spray the quackgrass when it's actively growing (spring or fall). Follow-up treatments may be needed. It may also yellow out the bluegrass for a short time. It comes as a granular product similar to "Manage" in a small plastic bottles. Mix it with water as well as a spreader/sticker. I'm thinking the quackgrass must be tall, then use a fine mist when you spray it (just like nutsedge). Call your local LESCO dealer, and also see Monsanto's website. I'm gunna try it soon. 30 years in the lawn care industry. I hope soon to become a senior lawn site member. Good luck.