I am seeding my large back yard with blue grama - 30-45 minutes of almost daily hand weeding for two months keeps me from falling too far behind on the green foxtail, bindweed, elm tree seedlings, pigweed, ragweed etc etc --- yet it's getting rather boring and tiring - now I am developing several pesky sections of annual bluegrass - is there a post emergent that can knock these sections back until I can use a preemergent in the fall and spring?
Alas, you are facing the Gardener's Dilemma-you prepare a large area with ideal conditions for plants to grow and then the wrong plants come up. The standard response to this is that a weed is just a plant in the wrong place. But that's not what you want to hear. And you also don't want to hear that hand weeding is the most effective and earth-friendly way to remove said unwanted plants. Blue grama is an excellent choice for a native lawn grass and is most effectively planted by seeding. In your climate and elevation in Southeastern Colorado it should form sod and be a perennial. Like its near relative, Bouteloua gracilis (buffalograss), often planted with blue grama, it is a high maintenance lawn, especially in the early stages. As you water and fertilize those seeds, many opportunistic weed seeds are waiting in the soil for the same tender loving care.
While herbicide intervention may be possible for some of the plants that are dicots or broad-leaved plants, the bluegrass is a grass, just as your blue grama is, and herbicides can't differentiate between two grasses. Since you are planning to use this as a lawn, rather than a grazing area, you might mow it two or three times a year to try to keep the annual weeds from reseeding.
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