How to Kill Nimblewill
To kill nimblewill, pull it out of the ground by hand or use a shovel to dig up the roots. You can also till compost into the soil so it drains better — nimblewill struggles in well-draining soil. To make it harder for nimblewill to get the nutrients it needs, spread new grass seed over your lawn and wait for it to grow — the new grass will take away water and nutrients from the nimblewill so it can't survive.
Use a selective herbicide if you do not want to kill surrounding plants. Selective herbicides are designed to kill certain weeds without harming other nearby plants. There is only 1 type of selective herbicide available for nimblewill, called Tenacity, which you can purchase online. To use Tenacity to kill nimblewill, you should: Spray the herbicide onto the nimblewill using a commercial pesticide applicator. Follow the instructions on the label to know how much herbicide to use. Apply the herbicide 3 times, waiting 3-4 weeks in-between applications. Do these applications in the summer when your grass is actively growing. If the nimblewill turns white, it means the herbicide is working. Use a non-selective herbicide for a more cost-effective solution. Unlike selective herbicides, non-selective herbicides kill any plants they come into contact with. However, non-selective herbicides are more affordable, so they are a good option if you are willing to regrow the plants around the nimblewill. To kill nimblewill with a non-selective herbicide, like Roundup, you should: Spray the herbicide onto the nimblewill using a commercial pesticide applicator. Wait until the summer when the nimblewill is actively growing to apply the herbicide. Wait up to 4 weeks for the herbicide to fully kill the nimblewill. Plant seeds where the nimblewill was so new grass and plants grow in its place. Apply a preemergent herbicide so the nimblewill does not come back. Preemergent herbicides prevent weeds from growing in the first place. You can find this kind of herbicide online or at your local gardening center. To use a preemergent herbicide, you should: Mix the herbicide in with the fertilizer you are adding while planting in the spring. Apply more herbicide during the summer after it is been a few months since the initial application. Wait for a clear, wind-free day to apply the herbicide. Herbicide application works best when there is not any inclement weather. Rain will wash away the herbicide before it absorbs into the nimblewill, and wind can cause it to spread to unintended areas. Put on protective clothing and eyewear before handling the herbicide. Herbicides can be dangerous if they get on your skin or in your eyes. Wearing a long-sleeve shirt, long pants, closed-toe shoes, gloves, and safety glasses will help prevent the herbicide from getting on you. Take a shower and wash your clothes separate from the rest of your laundry after applying herbicide to remove any traces of it. If you accidentally get herbicide on your skin, wash the area immediately with soap and water for 15-20 minutes. If you accidentally get herbicide in your eyes or mouth, call Poison Control. Read the application instructions on the herbicide label carefully. Using an herbicide incorrectly can be dangerous and it could damage your lawn or garden. Always follow the instructions on the label to see how much herbicide you should use and how it should be applied. Pull out the nimblewill by hand. Nimblewill can easily be pulled out of the ground by hand. However, you must pull up all of the roots so the nimblewill does not grow back. You may want to use a shovel to dig all of the nimblewill's roots out of the ground so there is less of a chance it will grow back. Improve the drainage of the soil the nimblewill is in. Nimblewill thrives in wet, poor-draining soil. Improving the soil drainage will make it harder for the nimblewill to survive. There are several ways you can make a soil drain better, like: Grading the soil so it is more level if it is located at the base of a slope. Tilling 2–3 inches (5.1–7.6 cm) of compost into the soil so it is more porous. Avoiding over-watering. If you are using an automatic sprinkler system, make sure it is not providing too much water to your grass and plants. Overseed the grass surrounding the nimblewill. Overseeding is the process of spreading grass seeds over grass that is already grown. Overseeding makes lawns and beds of grass more dense and lush, which makes it harder for nimblewill to compete for nutrients. To overseed a lawn or bed of grass, you should: Spread your desired grass seed over the lawn or bed of grass in late summer or early fall. Wait until the following growing season for the new grass to grow in and out-compete the nimblewill. 
Use a selective herbicide if you do not want to kill surrounding plants. Use a non-selective herbicide for a more cost-effective solution. Apply a preemergent herbicide so the nimblewill does not come back. Wait for a clear, wind-free day to apply the herbicide. Put on protective clothing and eyewear before handling the herbicide. Read the application instructions on the herbicide label carefully. Pull out the nimblewill by hand. Improve the drainage of the soil the nimblewill is in. Overseed the grass surrounding the nimblewill. 