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You should wait seven days prior to overseeding after Roundup application to ensure thorough translocation of the herbicide. Roundup will kill all desirable turfgrasses so it should be used only for spot treatment or where total renovation is desired. Please read: Weed Control Strategies When Overseeding at this link: https://archive.lib.msu.edu/tic/mitgc/article/1990123.pdf

You may also want to read this: Avoid applying herbicides this spring, i.e., no fertilizer plus crabgrass preventer or weed-and-feed products. Young seedlings don’t tolerate herbicides very well and the guideline is usually to wait for three "real" mowings before applying any herbicides or in some cases at least 60 days. Real mowings mean you’re actually cutting grass, not just running over the area to trim down any weeds. Check out: Tips for reseeding lawns in spring - Kevin Frank, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences - April 20, 2018 - Spots of your lawn may need reseeding this spring. At this link: https://www.canr.msu.edu/news/tips_for_reseeding_lawns_in_the_spring