Now is the time to use Roundup or carefully dig the plants by hand. Don't rototill or you'll spread the little tubers all over! It can be gotten rid of (with persistence).

The small tubers/bulbettes of this very invasive plant are easily spread by rototilling, digging, transplanting and even dividing other plants where the tubers are growing side by side. March is the time to attack--I've been trying to control this plant on two separate properties (mine) over 15 years. It can be greatly reduced and in some cases eliminated through persisitance. I carefully hand pull the enemy from my garden beds. I will admit to doing little with it in the lawn--if you could call my spring melange of ajuga, lesser celandine, naturalized bulbs a lawn.

Lesser celandine is emphemeral and disappears in the heat at the end of May, so if you are going to continue to try and eradicate it, you have to mark where it is now...

I also have it and have been working to remove it for the past four years. In the beds I have carefully applied roundup and it's just about gone. In grass, I took a 1" piece of copper pipe and made a tool that looks like a soil probe and has a ground opening on the edge of the pipe. I have a cross handle drilled in the pipe made from a 1/2 inch dowel. I push the pipe over the plants in to a depth of a couple of inches and remove a plug that captures the tubers. I've done this the past two years and I can see progress, though it takes persistence.