This is definitely a broadleaf weed and its heart-shaped leaves suggest it is wild violet. This weed is very difficult to control, especially this time of year.

The most effective approach would be to use the vegetation killer glyphosate (Round-Up). Dab it on the leaves. Some people use a paintbrush or sponge for this. Do not get this chemical on your lawn grass or it will kill those grass plants.

The most effective time to kill this, and other perennial weeds will be in mid to late September. These weeds start to move their nutrients down into their roots at that time. If you spray a herbicide on a perennial weed at that time it will naturally channel the weed down into its roots.

Wild violets will have purple flowers. Did you see them earlier this year? Maybe you can GOOGLE wild violets and look at the internet images to see if it matches with your weed. I usually do not see much wild violet in our part of the state. It is more likely found in shady, forested areas.

Violet or not, this is clearly a broadleaf weed. You can kill it with glyphosate as mentioned above. Another option is to spray it with a broadleaf weed killer, such as a Trimec formulation. Weed-B-Gon Plus Crabgrass Killer is one such product. These broadleaf weed sprays can be sprayed on the lawn and will not kill the grass.

You will get a much better kill if you wait until September. We generally frown on using broadleaf weed killers at this time of year because the lawn is under stress now from heat and there is a risk of the herbicide drifting to nearby gardens and trees.

Trimec is generally a very effective weed killer, but violets are especially hard to kill. That is why I started our discussion with glyphosate.

Let me know if you have any other questions.

Regards,
Tom Kalb, Extension Horticulturist, NDSU
e-mail: <personal data hidden>