I'd just kill it dead, using Oust and then again with atrazine and gly but plant it at a low rate. In theory you should have a thin enough stand that nature will fill in the voids and you'll have room to plant some shrubs or trees if you want to speed it up. I went the nuked seedbed route and had deer bedding the very first year. The following years I had undesirables start to join in. This year I mowed all my Kanlo and CIR at probably 3.5' tall because I couldn't stand to see the Canada thistles in it. The thistles hated being mowed and I'm really happy with how the switch looked this year... nice and clumpy and just has that "deer" look to it. Even after being mowed the switch still grew more than tall enough. I'll enclose a pic of how it looked yesterday. I can't use fire where I'm at, just a mower. Here's a new and improved version of Cave in Rock if anyone wants to give it a try. Says it can do well in WI and MI.
https://alseed.com/product/rc-big-rock-switchgrass/?v=a4e19ce04d72
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