The Collaborative International Dictionary of English v.0.48:

Devitalize \De*vi"tal*ize\, v. t.
   To deprive of life or vitality. -- De*vi`tal*i*za"tion, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

devitalization
    n 1: the act of reducing the vitality of something [syn:
         devitalization, devitalisation]