The issue: Water hemlock

Water hemlock (Cicuta douglasii or Cicuta maculata), a perennial, is the most poisonous native North American plant. All parts of the plant are poisonous to warm-blooded animals. The plant typically grows in wet areas of pastures, ditch banks, and swamps. The plant tissues are still toxic in silage or dried hay.

Water hemlock grows three to seven feet tall; it has bi- or tri-pinnately compound leaves, leaflet margins are entire and toothed, leaflet veins extend to the notch rather than the tip of the teeth; the white flowers are borne in umbrella-shaped clusters. Stems may have a purple tint to them. The stem base/root top has compressed chambers which exude a highly toxic fluid. The plants have roots and tubers (an underground stem structure).

Water hemlock reproduces by seed and tuber sprouts. Killing the root and eliminating seed production is essential for control. The seeds only remain viable for two to three years in field conditions. Seeds may spread through water, soil, equipment or animal movement.

Integrated pest management options:

· Prevention: Keep ditch banks free of seed-producing weeds; identify and control new weed infestations; feed weed-free hay; clean farming, recreational, and construction equipment and machinery between fields.

· Mechanical: Hand-pull, removing as much root as possible. Dispose of all plant parts. Wear gloves and eye protection.

· Cultural: Don’t overgraze pastures; manage land to provide good competition from desirable plants; drain swampy areas if possible.

· Biological: None.

· Chemical: Late spring or early summer before seed formation; 2,4-D, glyphosate, or picloram (restricted use). Be sure the weed and landscape or crop situation are listed on the label. Always read and follow herbicide label directions.

Combine them:

Combine different IPM options over a period of years to help improve the effectiveness of your efforts.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County.

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