How Can I Control Poison Hemlock?

Do you have a small infestation?

Do you want to control poison hemlock by repeated cultivation or mowing?

Do you want to try preserving natural enemies of poison hemlock?

Do you want to control poison hemlock chemically?

Hand removal is recommended for small infestations. When pulling the plants, the entire taproot should be removed to prevent regrowth. However, care must be taken with manual control to minimize soil disturbance that can encourage further germination of seeds at infested sites. Solid carpets of hemlock seedlings aren't uncommon following soil disturbance.

Plowing or repeated cultivation of newly germinated plants will prevent poison hemlock establishment. In areas where cultivation isn't practical or possible, repeated mowing once the plants have bolted but before they have flowered can reduce further seed production. Routine mowing reduces poison hemlock's competitive ability, depletes its energy reserves in the taproot, and prevents seed production. Close mowing has the additional advantage of reducing the amount of toxic leaf material available for livestock grazing.

The European Palearctic moth, Agonopterix alstroemeriana, is the main herbivore feeding on poison hemlock. This moth was probably introduced by accident, and poison hemlock is considered its only known host plant. The larvae live in conspicuous leaf rolls and feed on foliage, buds, and flowers in spring and early summer. The adult moths emerge in summer and can be found from June until March of the following year. Despite its widespread occurrence, the moth isn't an effective control agent for most infestations of poison hemlock.

Although several herbicides are available for controlling poison hemlock, herbicides should be used only on seedlings or small rosettes and not on fully mature plants. Herbicides like 2,4-D, triclopyr, and glyphosate, available to both residential users and small non-commercial operations, may be a more effective option than mechanical control only with larger infestations.

It is important to prevent a small-scale infestation of poison hemlock from becoming a more significant problem. This can be accomplished by periodically inspecting the area for newly established plants. Once identified, remove individual plants by hand pulling, hoeing, or spot application of an herbicide. Wear gloves to minimize direct contact with the toxic sap. It is essential to prevent isolated plants or a small cluster of plants from producing seeds. Don't burn plants or plant debris, because burning may release toxins into the air. Use certified weed-free hay to prevent poisoning livestock.