From The Collaborative International Dictionary of English v.0.48 :
Unfertile \Un*fer"tile\, a.
Not fertile; infertile; barren. -- Un*fer"tile*ness, n.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
unfertile
adj 1: incapable of reproducing; "an infertile couple" [syn:
sterile, unfertile, infertile] [ant: fertile]