Well it's a fungicide, developed bythat also kills worms so I don't like it already. Apparently you can't kill a rat with it but if you feed them a lot for a long time it may get a liver problem so it is not really that directly harmful. There have been some links with problems with development of the optic nerve in unborn children which lead to it being banned in Australia. Apparently it is still widely used for celery and grapes and flowers.
It has been know to cause allergic reactions in workers who are exposed. It is slightly toxic to Birds and very toxic to Fish so that does not sound to good.
All in all it's not likely to do you any direct harm but will kill most of the wildlife surrounding the field!
Think of the worms. Don't use it.
http://www.apvma.gov.au/chemrev/benomyl.shtml http://www.pesticideinfo.org/Detail_ChemUse.jsp?Rec_Id=PC32865 http://extoxnet.orst.edu/pips/benomyl.htm http://www.pan-uk.org/pestnews/actives/benomyl.htm