You need to understand that pre-emergent herbicides have NO effect on any existing weeds. These will either need to be removed manually or treated with a post emergent herbicide like RoundUp or any lawn weed killer. Pre-emergents only prevent seeds from germinating or fully developing after germination. And different pre-emergents typically address different types of plant seeds.

One of the most effective pre-emergents for crabgrass control are herbicides that contain pendimethalin as the active ingredient. Or look for dithiopyr (Dimension) which offers both pre-emergent and some post emergent crabgrass and broadleaved weed control. Trifluralin is also registered for Bermuda grass, so that is an option as well.

Follow directions on the label as to rates and frequency of applications. You may not have sufficient time for three applications before you plan to replant but the good thing about pre-emergents is they will have no impact on fully developed plants you will be including in September. So completely safe (except the dithiopyr) to apply after planting or later in fall or next spring.

gardengal48 Thank you for that informative post.

So it sounds like I dont need Roundup as the lawn with all its weeds were dug out. I know have dirt only with some stringy grass roots or weed roots. I'm thinking of tilling the dirt as it is very compacted and sifting out the roots (because will they grow again?).

I will apply a pre emergent with a dithiopyr for the crabgrass now. You mentioned that it was not safe after planting. Does this mean that it will kill my perennial plugs? How many applications does it usually require? Then I will spray Trifluralin later if the bermuda shows up. It isn't very much so I think I'll just wait. I'm putting down 4 inches of arborist chips so hopefully that does most of the work for me.