'weedkiller injecting'

Not every day you see people in hazmat suits in the park!
Have seen them here for the past few days. When I first saw them I thought it was some people playing a role-playing game, until I saw the warning signs advising that there were 'weedkiller injecting' works in progress.
I can only assume that they’re trying again to get rid of the American Skunk Cabbage.