The white flowers develop into green, ridged seed capsules which turn brown when the seeds mature. Poison hemlock must be removed. Do not allow this weed to go to seed. Wear gloves when handling it. Don't put it into the compost.
Dead stalks can remain poisonous for two or three seasons.
The herbicide 2,4-D applied to the early stages of growth will kill it. If you need more help identifying this or other weeds, contact your local Noxious Weed Control Board. They will help with photos and information about getting rid of the weed.