Allium canadense can be controlled with a three-way weed killer such as Trimec, Weed-out or Weed-B-Gon.

If you only have a few, digging them out is a good answer as well.

hortster

This post was edited by hortster on Sat, Apr 5, 14 at 12:12

You can spend a lot of money on poisons that may work for a time and will need repeat applications or you could take a good look at the soil they grow in and correct them which will result in long term control.
In my experience both the garlic and onion grow in poor soils the limit grasses ability to grow.