I'm trying to identify a weed in my garden. I don't remember seeing this weed before - or if I did, it certainly wasn't in this quantity. The leaves are long, narrow, lightly fuzzy, and slightly toothed. The roots are sometimes a single, long root, and sometimes a long vining root with the plants rising from it. I'm attaching photos. Any help you can give would be greatly appreciated!
Mesa County Colorado weeds invasives
I'm sorry to say that it appears that you have white top, aka hoary cress, Cardaria draba. It can be a challenge to control. It does respond to herbicides, but one treatment will not be sufficient - it will take persistence, probably for several years.
Both glyphosate (Round-Up and many other brands) and 2,4-D will provide some control - the choice has to do with where the weed is growing. In the lawn, 2,4-D won't harm the grasses, but in a garden it's more of a problem. You may have to find a way to isolate the plant (such as removing the bottom of a can to form a tube, placing it over the weed and spraying into the can.)
One of the most effective chemical treatments is to combine glyphosate and 2,4-D. Mix these chemicals according to the label directions, but put them into the same gallon of water. Be careful with this mix - it's potent and will affect any plants it contacts!
The timing for chemical treatments for white top (and other flowering perennial weeds) is when the plant is in bud - which here on the Mesa County fairgrounds is right now. Fall is also a good time.
Unfortunately, non-chemical management practices such as pulling or mowing will do little to control this plant - you'll just have to keep repeating this process. Since white top is an aggressive seeder, you will definitely want to prevent it setting seed by removing the flowering tops.
Good luck with it!