Pull it now, before it sets seed and drops a jillion seeds to provide you with years of future "crops."

Pull it or trim it? there must be 500 hundred plants there. I pulled some, I think it spreads through rhizomes. I have to bend like 50-100 times to pull them all and my back hurts :-)

Well, if it spreads by rhizomes, cutting won't do anything to slow it down.

Show us an entire plant, including the roots.

Looks like spreading chervil, Anthriscus sylvestris. A known invasive.

If so, not rhizomatous. Start pulling before the seeds drop.

It looks a bit too loose and airy for Anthriscus sylvestris, which lines miles of our roads in May. A view of the whole plant and some shots of the larger leaves at the base of the plant would help.

To avoid all the bending use a garden fork to loosen the roots and lift the plant. Or work from a kneeling/crouching/sitting position.