it's definitely not nutsedge, which has a different and distinctive look. first question to ask yourself:is it the exact same grass as the rest of your lawn? if it is, then extra water or fertilizer in that area is producing extra fast growth. If it's definitely a different plant, then you have a weed grass in there. I've had that. Big mess. Hard to get rid of. Good luck

Agree. The very best time of the year to seed a northern lawn is in the early fall. Every day after that is worse than the previous day. Once you get past late winter, the results are MUCH less satisfactory headed into spring, late spring, and summer. The later it is seeded the faster it dies out and the faster the crabgrass takes over. At this point all you can do is sit it out. You can practice good lawn care management for the next couple of months and plan to renovate it in late August. Here's what to do until then. Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall. Mulch mow at the mower's highest setting. Fertilize now with an organic fertilizer like soybean meal, alfalfa pellets, corn meal, corn gluten meal at a rate of 15 pounds per 1,000 square feet. Don't use any chemical fertilizers, herbicides, or insecticides until later. By allowing the weeds to grow you will be developing the soil and putting roots down into it. These roots are important for your soil to develop the right structure. Then in August do this: Change your watering practices to every day, 3x per day, for 5-15 minutes each time. Do that to sprout all the weed seeds in the soil. After a week of daily watering, spray everything with Round Up to kill all the living stuff. Continue with the daily watering for another week and spray again with RoundUp. This process should clear everything out. Rake up all the dead stuff and you can seed right onto the top of that soil. Roll the seed down or walk on every square inch of it. Then continue watering daily 3x as before to germinate your new grass seed. This approach will give you a pure stand of grass almost guaranteed. When you get 80% germination on your grass seed, start to back off on the watering frequency. Mow when the grass is tall enough to mow at 5 inches or so. At that point look to see if the grass is uniformly dense across the yard. You still will have time to add more seed in the thin areas.

May is the third worst month to seed northern grasses in your area. Only July and June are worse. So that is part of the reason you have so many weeds. To someone's credit, though, I would have expected far more weeds than grass by this time of year. You're doing something right!! The garden center that sold you the seed in May should be off your list of future purchases, because they don't give good advice. Based on that I also question the quality of their recommended seed. You have plenty of time to overseed this year. Fall is the time to seed. New York is a big state. If you live in the north then start with the herbicide now to seed in early Sept. If you live in the south then you can wait a week or two and seed later in Sept. Seeding early in the fall gives the new grass time to come in and for you to evaluate whether you need to thicken it up with more grass seed. Go back and reread gardengal's first post in this topic. She has a very good way of explaining those concepts. There are many Weed-b-Gon products. "Basic" WBG is a 2,4-d product, at least in my neighborhood. A slightly different product is Weed-b-Gon Chickweed, Clover, and Oxalis Killer. That one has Triclopyr (longer wait period). Formulations for these products may vary from state to state as different regulations apply. I would suggest you read more here on this forum to see what you can learn about lawn care. You can't rely on TV ads to tell you when to do things. Here are some general concepts that have become common knowledge on this and other lawn forums. New seed (northern grasses) should be applied in the fall. Weed n Feed products rarely work as advertised. Spot spray herbicides work better. Deep and infrequent watering is the way to go. Frequent watering leads to shallow roots and general brownish appearance. Spring fertilizer should go down late, not early. Wait until May or late May. Fall winterizer goes down after the grass has stopped growing but before total dormancy (before you have regular freezes). For most this is around the end of November. Mulch mow always. The clipped grass returns valuable organic material to the soil. Mow most grasses at your mower's highest setting. This leads to deeper rooting. Deep roots take advantage of moisture and nutrients deeper in the soil.

Photo is pretty indistinct but possibly violets. And violets tend be one of the more persistent lawn weeds to control. You can try Trimec, Spurge Power, Ortho Weed-B-Gon Chickweed, Clover and Oxalis Killer or anything with triclopyr as an active ingredient or whatever lawn weed herbicide that lists "wild violets" as a weed that is controlled. Follow directions carefully and be prepared to make multiple applications.