I have used roundup for a number of years in all my apiaries for total weed
control.Nature abhors a vacuum and as soon as the ground is bare vegetation
tries to reastablish  so repeated applications are needed(1 or 2 per year in
southern England). Some years ago I read of some Australian research where
Roundup had been fed to bees in syrup with little or no ill effect but I
dont have a reference for this. Even so I have always sprayed at night
taking care not to spray hives more than absolutely necessary and have never
had any problems. To kill the thistles but  not the grass there are
selective herbicides available but seek professional advice from a qualified
agronomist regarding bee safety and which products are passed by the
pesticide regulatory people in your area.
      An alternative" organic" approach which works on English creeping
thistle--Cirsium arvense ---is to mow the plants off just as they are about
to flower when reserves of energy in the plant are at their lowest. This may
take 2 or 3 seasons to be totally effective.
      Lastly thistles are a wonderful source of nectar for our little
friends and in England Gold Finches love to feed on thistle seeds.
 
Peter and Barbara Dalby, England
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