When replacing bluegrass with new fescue sod should I use a sod cutter or tiller to get rid of the old grass?
El Paso County Colorado
If your bluegrass lawn has any weedy grasses in it (bermudagrass, quackgrass, tall fescue and others), a sod cutter is likely to leave enough parts of these weedy grass plants behind....to regrow/reappear in your new fescue lawn.
A rototiller could injure tree roots or sprinkler lines under the existing bluegrass lawn. Further, "rototilling the bluegrass under" WILL leave plenty of bluegrass plants viable and close to the soil surface, ready to re-grow and become a problem in your new fescue lawn.
Your best option would be to spray glyphosate herbicide (Roundup and other trade names) on the entire bluegrass lawn when it begins growing rapidly (sometime in April). Wait 10-14 days, then reapply glyphosate to any still-green grasses or areas in the lawn. Wait another 10-14 days. This should kill all the bluegrass and most of any weedy grasses that might be in it (except bermudagrass - if you have any of that, it's a whole different ballgame!).
THEN, use a sodcutter to remove a fairly thin layer of dead grass and dead roots off the surface.
This leaves most of the topsoil intact and provides a good rooting medium for the new fescue sod.
As with any pesticide, read and follow herbicide product label directions carefully.