The Collaborative International Dictionary of English v.0.48:

Weed out \Weed out\, v. t.
   to selectively remove; same as weed[2], v. t.; -- of things
   that are useless or harmful.
   [PJC]

WordNet (r) 3.0 (2006):

weed out
    v 1: remove unwanted elements; "The company weeded out the
         incompetent people"; "The new law weeds out the old
         inequities" [syn: weed out, comb out]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "weed out":
   abstract, avulse, backset, cast off, cast out, chuck, clear,
   clear away, clear out, clear the decks, cultivate, culture, cut,
   cut out, delve, deport, deracinate, dig, dig out, dig up,
   disentangle, dispose of, draw, draw out, dredge, dredge up, dress,
   eject, elide, eliminate, eradicate, evolve, evulse, excavate,
   excise, exile, expatriate, expel, exsect, extract, extricate,
   fallow, fertilize, force, get out, get quit of, get rid of,
   get shut of, gouge out, grub up, harrow, hoe, liquidate, list,
   mine, mulch, outlaw, pick out, plow, pluck out, pluck up, prune,
   pull, pull out, pull up, purge, quarry, rake, rake out, remove,
   rip out, root out, root up, spade, strike off, strike out,
   take out, tear out, thin, thin out, throw over, throw overboard,
   till, till the soil, unearth, unravel, uproot, weed, withdraw,
   work, wrest out