Answer: It is difficult to control water hemlocks, but with persistence it can be done. The best way is to dig the plants up, roots and all. The only herbicide effective against water hemlock is Round-Up (glyphosate) Timing is important, though, so apply Roundup just as the plant comes into flower, but before seed set. Glyphosate also kills grass, and any other plant it comes in contact so spot treat with care.
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