Three-cornerd leek

My garden is being overgrown by Three-Cornered Leek (Allium trriquetrum) which grows from a white bulb and produces long linear leaves from the base and a cluster of white flowers. It seems to spread by growing more tiny bulbs which produce new plants, but it may also spread by seeds from the flowers. I am trying to dig up the bulbs but many are in amongst the roots of plants I want to keep.  I am told that a systemic weed killer (Glyphosate) might be effective and I have found a version (Roundup) in a gel form for wiping on leaves in the hope it will not kill the entwined wanted plants. Does someone have advice to give on eradicating this invasive and unwanted plant.