The picture content is not available but looking at your zone, the grass most often confused with crabgrass is dallisgrass. When you write back, tell us where you live.

First contact your local office of the Clemson USDA Cooperative Extension Service and the can help identify that and can also help you get a good, reliable soil test which might do as much to control this as anything else. Many "weeds" grow in soils that are not good soils for turf grass and turf grass most often needs a good, healthy soil or it will not grow well. At the same time dig in with these simple soil tests, Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top. 2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up. 3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart. 4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell. 5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy. to learn more about the soil you have and what yo need to do to make that soil into something that will grow a good, healthy turf. Here is a link that might be useful: Clemson CES

It kills those particular weeds permanently. However there may be seeds that germinate afterwards and grow. It kills the weed plants but not the seeds. If the weeds have dropped seed before they're killed, you will get more weeds when the seeds sprout. Or seeds can be blown in from elsewhere. It seems like if there is bare earth anywhere, weeds will take over. I use Weed B Gon and Weed B Gon CCO, usually just once a year in late spring. They are different and kill different weeds but together take care of most. They do not hurt the grass. They will hurt ornamental plants and trees so you have to be careful to spray when the wind is not blowing and when the air temperature is not too hot. Read the directions. If you have crabgrass, pre emergent will keep it from sprouting. You put it down when the forsythia blooms. Broadleaf killers don't kill crabgrass.

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.