Bees HATE weed eaters.  GUARANTEED!!!  They aren't fond of lawn mowers
either, but they HATE weed eaters.  Another alternative is to mulch around
your hives to keep the weeds and grasses from growing.  As any organic
gardener will tell you, a thick mulch will keep the vegetation from
growing and eliminate the need for close trimming.  Mulch will retain
water, hence encourage wood rot, so a good strategy is to have your hives
on an inorganic stand (cinder blocks are ideal), mulch heavily around
the stand (a bale of staw or lawn clippings or even a sheet of cardboard
works well) and no grass will grow, eliminating the need for weed wacking.
 
I use a combination of mulch and the lawn mower.  I used to use a combination
of lawn mower and weed eater for close trimming, but my bees convinced me
that mulch was the way to go.  Wanna buy a slightly used weed eater? ;)
 
As always, your results and/or preferences may vary.
 
Aaron Morris - I think, therefore I bee!