Hi,

It looks as if you have a fairly well established stand of crabgrass there, along with some common blue violets. Crab grass is a summer annual grass species and can typically be easily controlled with a weed preventer, as you mentioned, but greater effectiveness is achieved when you are maintaining turf. The presence of crabgrass in the lawn indicates that you may have some underlying issues with how the lawn is being managed.

The best defense against weeds in the lawn is a healthy stand of turf. Turf is healthiest when mowing heights are kept high, over 3 inches, and when the lawn is adequately fertilized. If you have not done a soil test in the past, I'd highly recommend doing one to address any nutritional issues you may have.

https://www.canr.msu.edu/resources/dont_guess_soil_test_get_your_home_lawn_and_garden_soil_test_kit_today

https://www.canr.msu.edu/resources/mow_high_for_weed_and_grub_control

That said, you'll still want to apply some crabgrass control to prevent the plants you currently have from dropping too much seed into your lawn for the remainder of this summer. "Summer annuals germinate in the spring, grow through the summer and die with the first hard frost. These plants produce a tremendous amount of seed in the mid- to late summer when the day length starts to shorten. These seeds ensure next year’s crop of weeds but can also remain dormant in the soil for several years before germinating. It is likely that if you have crabgrass in your lawn, it will be there next year, too. “One year's seeding equals seven years weeding,” as weed scientists like to say."

https://www.canr.msu.edu/resources/crabgrass-control-in-home-lawns

Some information on how to best time your weed preventer applications for next spring: https://www.canr.msu.edu/news/timing_crabgrass_pre_emergence_applications

The common blue violets, Viola spp., are a broadleaf perennial that spread by underground stems called rhizomes. It can be somewhat difficult to control, but with correctly timed herbicide applications, you can reduce it with time. Many people choose to leave it in their lawns these days, since it's a native plant that provides benefits to pollinators.

Here's some information regarding control of that plant: https://extension.psu.edu/lawn-and-turfgrass-weeds-wild-violet

If all of this sounds like too much to manage, it's okay to turn to a licensed lawn care company to help get your lawn back in better shape. 

What to look for in a lawn care provider: https://ohioline.osu.edu/factsheet/hyg-4025-88

Once these issues have been adequately addressed, it should be easier to maintain a more weed-free lawn as long as you provide adequate fertilizer, watering, and keeping your mowing height higher.