I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
It is best to kill the grass/weeds there first and then rototill the area and lay the new sod. Depending on the type of grass and weeds you have currently the need to kill them first will vary from slightly important to very important.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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