Dealing with poison hemlock

Asked April 30, 2020, 5:06 PM EDT

We have an abundance of poison hemlock. After viewing several sources online, I'm certain of the type of weed I have. What is the best way to get rid of it? Is there any way to slow or prevent its growth?

Linn County Oregon

1 Response

Poison hemlock is a noxious weed in Oregon and can be managed with proper precautions to avoid exposure to the toxic compounds it contains. From OSU Extension:

"Mechanical treatment

Plowing or repeated cultivation will prevent poison hemlock from establishing. Digging poison hemlock can be effective when caught early and the plant population is small. Take care when digging or mowing poison hemlock. Wear rubber gloves and a mask when handling this plant. On a hot day, the plants’ toxins may be absorbed into the skin.

Do not burn the plant, as the smoke can contain deadly toxins.....


Treating poison hemlock with herbicides is most effective in late spring or early summer. Several combinations of herbicides are effective, including 2,4-D plus dicamba (2.5lb + 1 lb a.i./acre). Glyphosate and triclopyr have also been used with success. Herbicides should be used on seedlings or small rosettes and not on fully mature plants for ultimate success. To achieve complete eradication, repeated applications may be required until the seed bank has been depleted.

Please use caution; herbicides sprayed within 50 feet of a body of water can pose significant environmental hazards and typically require an aquatic herbicide. Be sure to contact your local weed control authority or OSU Extension for specific herbicide recommendations, and check the herbicide label for restrictions."

The active ingredients mentioned come in formulations for home gardens that are available from garden centers. Many will have a recommended application rate for hemlock.

I hope those tips are helpful, this is a difficult weed that will need multiple treatments, whichever methods you choose. Keep after it and you can reduce it over time.

Please reach out if we can assist further.