That spiky bright green stuff you see sticking up in the middle of the photo? That’s summer’s version of wild onions–yellow nutsedge. And just like with wild onions or wild garlic, control is difficult to near impossible. In fact, we and most of our neighbors do not even try at this point, and here’s why.
This is not a grass or a weed; it is a sedge. A sedge is a particular type of plant–you’ll often see ornamental varieties of them being sold in the garden centers with the grasses. But because of this, neither herbicides nor broadleaf weed killers are going to work to kill them. So things like Round-Up (glysophate) and even the pre-emergents are not going to have any effect on this plant.
To make matters even worse, it grows from a bulb-like structure underground, so hand pulling is going to be difficult. If you try when the plants are young, it may be possible. By the time the plants are this mature, it is all but futile. This information sheet from the University of Vermont extension service shows all stages of the plant including its bulb-like structures and the mature fruiting bodies that give it the name “nutsedge.”
There are a few herbicides that do work on this plant but they are not commonly available to the homeowner and as such I surely cannot recommend them. Should you have a nutsedge invasion, I would advise you to work with a professional to carefully control it since it is a perennial weed and it will be back next year.