The Collaborative International Dictionary of English v.0.48:

Plaga \Pla"ga\ (pl[=a]"g[.a]), n.; pl. Plag[ae]
   (pl[=a]"j[-e]). [L. pl[=a]ga a blow, a welt, a stripe.]
   (Zool.)
   A stripe of color.
   [1913 Webster]