The Collaborative International Dictionary of English v.0.48:

Defoliate \De*fo"li*ate\, Defoliated \De*fo"li*a`ted\ a.
   Deprived of leaves, as by their natural fall.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

defoliate \de*fol"i*ate\, v. t. [LL. defoliare, to shed leaves;
   L. de- + folium leaf: cf. F. d['e]foliation.]
   to cause (a plant) to shed its leaves.
   [PJC]

WordNet (r) 3.0 (2006):

defoliate
    adj 1: deprived of leaves [syn: defoliate, defoliated]
    v 1: strip the leaves or branches from; "defoliate the trees
         with pesticides"