Ok, I am a first time homeowner struggling with a serious bout of
crabgrass. I bought my house in November, and when the weather
started getting nice out, I spent a lot of time and money on my lawn
making it look nice, which it did, until about late May, when
crabgrass just overtook about 80% of my front yard and 60% of my
backyard.

This occured about 1-2 weeks AFTER I used Scott's Lawn Builder with
crabgrass preventer on it.

Did I not use the crabgrass preventer early enough? Most
documentation says that it should be used in early May. It mid-May
too late?

And now that my crabgrass is in full bloom, is there any way to kill
effectively? I tried spraying a ready-to-use Bayer product on it, to
no avail! Should I mow high, or low?

Thanks!