I sprayed my lawn with roundup . a week later i tilled ,raked and seeded . and installed a irregation system. It did not kill the crabgrass. my lawn is about 60 percent crab grass . approx 3/4 acre . can you please give me a step by step and when i should apply .
We are happy to help.
You don't mention the timing of when you did all that work. The timing is pretty important for success. The best time to seed your lawn is in late summer into fall.
There is a second window, not quite as good in the March/April timeframe. This is not as successful because that is the same time that crabgrass (which is an annual that dies in winter but re-seeds each year) gets going.
Crabgrass is best controlled by using a spring application of pre-emergent herbicide which stops germination. The timing to put that down is when the yellow forsythia bushes bloom. That said, some years, because of weather conditions, a second application may be needed.
Here is our page on Crabgrass and it's control: https://extension.umd.edu/hgic/topics/crabgrass
and here is our page on Lawn Renovation: https://extension.umd.edu/hgic/lawns/lawn-renovation
the very best step-by-step information on Lawn overseeding and renovation is found here (which is the first resource link on the page above):
So i should seed in the fall and use a pre emergent in the spring
The HG102 publication linked above has step-by-step instructions for best results.