Somewhat ironically... actually using an Alcubierre drive has been theorized to...

...well, basically, when you 'come out of warp speed', turns out you've been accumulating, and energizing, a whole bunch of exotic particles and radiation along the threshold of your 'warp bubble'...

... so when you uh, decelerate/stop fucking spacetime so hard... you spew out an immense amount of exotic particles and radiation.

https://arxiv.org/pdf/1202.5708

So you wouldn't even have to nuke it from orbit.

You just have to come out of warp right next to your target planet, and that'd probably boil off a good portion of its atmosphere, and give everything biological on the side facing you lethal radiation poisoning.