Rate seems really high?

here is the lable: http://www.kellysolutions.com/erenewals/documentsubmit/KellyData/OK/pesticide/Product%20Label/10404/10404-88/10404-88_Lesco_Stonewall_020__Plus_Fertilizer_007_Mini_Fertilizer___701080__7_5_2013_12_04_19_PM.pdf

max rate is 17.2 lb/1k sqft per year.

But my question is if the info the guy from SiteOne is correct, will it kill my existing grass like they said it would.

I don't understand your reasoning. If you have a box of pain killers that says maximum of 8 pills a day, do you take 8 pills every day whether you have a headache or not just because it says max 8 pills?

I have bad crabgrass and dallisgrass i am trying to get rid of. The pre emergent didn't keep all of the weeds out and I just want to ensure that I don't get a 2nd round of them coming up after treating with my post emergent. That is why I am asking here what is recommended. If I have pain I can feel it and would know when to take the medicine, but with weeds I can't see what is going on below the ground and if I am going to have them come up, so I just assumed that it is best to put the whole allowable amount down. This is my first year at using a pre emergent. When the label shows 4 different recommended settings how am i supposed to know which to go with?

Where are you located? What kind of grass do you have?

North Texas just north east of Dallas. It is a bermuda grass.

thanks, that makes sense. I was trying to do the pull/dig thing last year when I started trying to get the yard looking better but the crabgrass and dallisgrass took off where they already had a good amount of ground taken due to me trying to get the soil right. I have been following a plan from Morph based on my LL test and it has really improved the grass, soil...and the weeds :). That is what got me to start with the pre emergent and post emergent control. I happened to find a bottle of MSMA that I had bought right before the ban so I put that down and it is killing a lot of them. I plan to follow up with another round of MSMA in a couple of weeks.

Our weed season is long up here too, so I might just stick to the quarterly thing as well. I would love to hear what others do around my area too. Also, has anyone ever heard of Prodiamine being a "root clipper" as the guy at the store said?

Most preM would be considered root & shoot inhibitors. Established Bermuda will just sluff off the affected stolons & get a little thatchy for a week. Those spots are easily fixed with a little light raking or one of those step aerator jobs from the box store to break up the dead matter & stimulate the Bermuda. It likes abuse.

:) thanks. I appreciate all the help here!

I'll give my 2 cents since I have bermuda and this is the exact pre-emergent I use.

I did the calculations in the past as I believe the bag rate is in annual applications per acre and I thought it was closer to 12.9 lbs/1000 sq. ft. I could be wrong. Either way, I think your logic is right. I have read to do split applications of stonewall. So for the sake of making the math easy, we'll use your number round down to 16 lbs/1000 sq ft and divide by 4. You want 4 applications at 4lbs/1000 sq. ft. You'll want to do one in the spring and the 2nd app about 8-10 weeks later. Same thing in the fall. As you somewhat hinted at, the goal is to make sure any weed that germinates later then expected will be caught by the 2nd application. I don't put down anything in the summer months as my grass is thick enough and I really don't have to worry about weeds. As long as you don't over apply or spill it, it will not kill your grass. I spilled some near my fence a few years ago and even though I cleaned it up as best as I could, nothing has grown back since then. 8.5 lbs for one application sounds like too much so I would discourage that. Lastly, this product has worked well with grassy weeds but not so well with broadleaf weeds. I have zero crabgrass or poa and I had some horrible poa a few years back. I spot spray the broadleaf weeds and my lawn looks fantastic. Hope this helps.

sherm, thank you!