I plan on planting imperial whitetail clover this fall. I have heard you need a cover crop the first year (maybe 2?) until the imperial establishes well. What cover crop would you go with: Crimson clover, wheat, oats, other?

I would use cereal rye at about 75-100lbs/acre. I've planted imperial whitetail clover and its some good stuff, but I've found that if I plant my regular fall mix and mix in durana that it does extremely well. Imperial clover is high dollar stuff. Once established, you can top sew cereal rye and brassica's into it the following fall.

I’m assuming we’re talking abouse a nurse crop...

Like blumsden said, cereal rye is good. I tend to like triticale for a nurse crop in clover too. Seems to be a little shorter when it matures. Doubt there’s a measurable gain/loss there though. Just me being me.

Kill the plot as soon as you can before it goes to seed if there is any wild rye grass, that stuff will suppress the heck out of clover.

To me, rye gets too high and the deer don't eat it as well, thereby leaving you with a lot of competition for your clover come spring. I'd go with wheat or triticale.

How about iron clay peas or lab lab?