Roundup is a nice product for killing unwanted vegetation. An extension
agent once told me he'd rather eat a spoonfull of roundup than one of
salt. I don't think I'd go that far, but it is very safe. Breaks down
within a week, and the area sprayed can be planted to a more desirable
species. I have sprayed in front of active colonies with no apparent
damage to the bees. I only found one problem with it. When used to kill
grass in front of hives, it works great - but - once the grass is dead,
herbaceous plants like nettles, burdock, thistles, etc, grow in its
place. I would rather have grass growing in front of my hives. After
killing the vegetation in front of a colony, consider planting a low
growing grass, or something like "New Zealand" clover that grows low and
thick and chokes out the herbaceous plants.