Last year I thoroughly sprayed all my crotons with Bayer 3-in-1 before moving them indoors, but I still had spider mite problems...
At some point when I was able to move them all outdoors during some mild weather I sprayed them with Murphy's Oil Soap after which I saw no more mites for the rest of the winter...
Coffee - either sun coffee from old grounds or diluted leftover coffee (non of that instant crap) - kills all sorts of bugs and arachnids. Makes me wonder why I still drink the stuff (while sipping coffee as I key this in). I've also used it on interior plants with great success. Plus I like the price!
Peyton, if they were already infested, it may have required more than one application. The idea is to use more as a preventative so control (if required) is easier. If applied repeatedly, the insect does develop a certain level of tolerance so it's good to use something else in your spraying cycle.
Some info gleaned today from the cycad chat board:
Systemic miticides include the following: KONTOS, Safari, and Trilogy
One member who claims to have a collection of old and new world croton cultivars mentioned that Avid kills mites but results in some unsusual leaf shapes on crotons.
Not sure if any or all of this is available in Florida or if one needs a pesiticide license or whatever.