Big, ugly, tomato-killing larva

[HudsonValley]

Went away for a few days and came home yesterday to find a badly wilted Cherokee Chocolate plant. Yanked the plant today, since it seemed hopeless, and found that an enormous larva had eaten half the roots! I'm guessing it's a cicada larva; I found a maroon-colored casing nearby.

Any idea how to kill its friends before they take out the rest of my plants? BT? GrubEx?

Here's a photo of the nasty critter, taken just before I sliced it in two (). The straw mulch at the top of the photo offers a sense of scale...