nucci60-
If you do this regularly, say, mid-summer and again in early fall, you should be fine. Arrow does grow a dense web of tough rhizomes, so don't get lazy and let it go some years. As for spading, that will work with a sharpened one if the ground is not too hard and rocky. I often simply use a long-handled set of pruners as the runners aren't very deep. I uncover the rhizome, open the pruners, put them in place, step down to push the jaws completely down around the root, and cut. Then I grab the cut end and pull out the rhizome. If the rhizome is hard to get out, just slip the sharp end of a pickax under the severed rhizome and pop it out using leverage on the handle.

I have seen some pretty nice groves of Japonica online in pics and in person that the only control they have had is regular mowing, resulting in a nice, tight hedge.