Figure 1: Poison hemlock stem, notice the purple coloring along the stem. Photo courtesy of Meaghan Anderson.

Poison Hemlock (Conium maculatum)

• Toxic Part: Entire plant, especially leaves and stems
• Risk: Highly toxic to all livestock (and humans); small amounts can be fatal
• ID Tips: Finely divided, fern-like leaves; purple-spotted stems; umbrella-shaped white flower clusters
• Notes: Often found in ditches and low-lying areas. Do not mow when flowering - can release toxins and spread seeds.
• Common look-a-like: Queen’s Anne Lace/wild carrot

Figure 2: Yellow, umbrella like flower cluster of wild parsnip. Photo courtesy of Meaghan Anderson.

Wild Parsnip (Pastinaca sativa)

• Toxic Part: Sap causes skin irritation when exposed to sunlight (phytophotodermatitis)
• Risk: Mainly a risk to humans (and pets) through skin contact; generally avoided by livestock, but ingestion can cause photosensitivity, and severe sunburn
• ID Tips: Yellow umbrella-shaped flowers; hairy and grooved stems; leaves look like celery or parsley
• Notes: Wear gloves and long sleeves when handling. Mowing before seed set helps control.
• Common look-a-like: Queen’s Anne Lace/wild carrot

Figure 3: St. Johnswort flower, notice the black specks on the petals margins. This Photo by Unknown Author is licensed under CC BY-SA.

St. Johnswort (Hypericum perforatum)

• Toxic Part: Entire plant
• Risk: Contains hypericin, which causes photosensitivity (sunburn-like skin damage) in light-skinned livestock such as sheep, cattle, goats, and horses. Severe cases can lead to skin sloughing, blindness, or death.
• ID Tips: Upright perennial with small flowers, flowers have five bright yellow petals that often has black dots on the petal margins; leaves are opposite, oval, and have translucent spots when held up to light; woody base; grows 1–3 feet tall in clumps
• Notes: Becomes more problematic in overgrazed or low-fertility areas. Most toxic when flowering. Often avoided unless forage is limited.

Figure 4: Milkweed growing in a bunch. Notice the large, pink flower clusters. Photo courtesy of Shelby Gruss.

Common Milkweed (Asclepias syriaca)

• Toxic Part: Leaves and stems
• Risk: Contains cardiac glycosides; toxic in large amounts, especially to cattle and sheep
• ID Tips: Thick oblong, opposite arranged leaves; milky sap; large round pink flower clusters; stems covered with dense pubescence
• Notes: Generally unpalatable unless forage is scarce. Monitor pasture for adequate forage growth.

Figure 5: Johnsongrass growing in a bunch, notice the branched seed heads. This Photo by Unknown Author is licensed under CC BY-SA.

Black Cherry (Prunus serotina) / Johnsongrass (Sorghum halepense)

• Toxic Part: Wilted leaves (Black Cherry); young regrowth and frost-damaged tissue (Johnsongrass)
• Risk: Both produce cyanide (prussic acid), which can be fatal within minutes
• ID Tips (Cherry): Tree with shiny leaves, dark bark, and white flowers;
  (Johnsongrass): Tall grass with prominent midrib, purple panicle seeds, spreads rhizomatous.
• Notes: Do not allow livestock access to wilted branches or frosted regrowth. Delay grazing after frost or drought.
• Common look-a-like (Johnsongrass): Sorghum species

White Snakeroot (Ageratina altissima)

• Toxic Part: Entire plant
• Risk: Causes “milk sickness” in humans through milk from affected cattle; toxic to cattle, goats, horses
• ID Tips: Opposite triangular leaves with serrated edges (sharply toothed) with three main veins; White flowers in flat-topped clusters;
• Notes: Common in wooded pastures or shaded edges. Control early; avoid grazing densely infested areas.
• Common Look-a-like species: bonesets, other snakeroots

Figure 6: Horsenettle seedling. In lower photo, notice the spines on the underside of the leaf. Photo courtesy of Shelby Gruss.

Horsenettle (Solanum carolinense)

• Toxic Part: Berries and leaves
• Risk: Contains solanine; can affect the nervous system and digestive tract
• ID Tips: Spiny stems and leaves; small, star-shaped purple flowers; yellow berries when ripe
• Notes: Toxic when consumed in large amounts. Spot spray or dig out to reduce spread. Berries are particularly toxic.

Figure 7: Cocklebur seedling. Photo courtesy of Meaghan Anderson.

Cocklebur (Xanthium strumarium)

• Toxic Part: Seeds and seedlings
• Risk: Toxic to pigs, sheep, and cattle; seedlings especially dangerous
• ID Tips: Rough stems with darks pots; sandpaper-like, triangular leaves with serrated leaf edges; hooked burs that cling to fur and clothing
• Notes: Can cause liver damage. Avoid overgrazing, as seedlings are more likely to be eaten when forage is limited.

Nitrate Accumulators
Some plants can accumulate toxic levels of nitrates, especially after drought or heavy fertilization:

• Common culprits: Pigweed, lambs quarters, Johnsongrass, and thistles.
• Risk: Nitrate poisoning reduces oxygen transport in blood—can be fatal
• Management Tip: Have suspect forages tested before grazing or feeding. Elevated risks following fertilization, and following drought breaking rains.

Figure 8: Field horsetail in both images. Photo courtesy of Shelby Gruss.

Horsetail (Equisetum spp.)

• Toxic Part: Entire plant
• Risk: Contains thiaminase; can cause neurological symptoms, especially in horses
• ID Tips: Hollow, jointed stems; no true leaves; resembles a bottle brush
• Notes: Grows in poorly drained soils and along ditches. Improve drainage and limit access.