I always carry a pair of pruning shears with me.

If I see poison hemlock I cut it. Here is what the foliage looks like

It blooms in May & June and can get 6' tall. Conium maculatum is the Old World plant which according to legend poisoned Socrates. This is a nasty plant, when ingested is toxic to both humans and livestock.

I first saw it on Lancaster Pike, Peach Bottom PA. It quickly spread to Cecil County MD. It has crossed the Susquehanna and is found in places never seen before. It is very noticeable when in bloom. It is biennial, I cut it with shears, it can also be sprayed with herbicide.