Flies, Lures and Baits:
The following classes of lures are authorized for use, except where restricted.
Natural and scented baits—A natural fish food such as bait fish, crayfish, frogs permitted as bait, grubs, insects, larvae, worms, salmon eggs, cheese, corn and other food substances not containing any ingredient to stupefy, injure or kill fish. Does not include flies or artificial lures. Includes dough bait, putty or paste-type bait, any substance designed to attract fish by taste or smell and any fly, lure or bait containing or used with such substances.
Soft plastic bait (unscented)—Synthetic eggs, synthetic worms, synthetic grubs and soft plastic lures.
Artificial Lure—A lure constructed of any material excluding soft plastic bait and natural and scented bait defined in (A) or (b)above.
Fly—An artificial lure constructed on a single-point hook, using any material except soft plastic bait and natural and scented bait as defined in (A) or (b)above, that is tied, glued or otherwise permanently attached.
I assume a or b refers to 1 or 2 but it is from the MDC definitions. Rubber is not a soft plastic.
http://mdc.mo.gov/about-us/about-regulations/regulations-and-permits-definitions