Pasture Risks on the Rise Weather extremes-flooding, drought, and overgrazing-are leaving Midwest pastures vulnerable to invasive toxic weeds. According to Shelby Gruss, forage specialist with Iowa State University Extension, opportunistic weeds like poison hemlock and wild parsnip are proliferating along roadsides and in thinned pastures, threatening livestock health.

"These weeds aren't just unsightly," Gruss explains. "They're toxic, and livestock may unknowingly graze them when other forage is scarce."

10 Toxic Weeds to Watch For Here's a detailed guide to ten of the most dangerous toxic plants currently found in Iowa and much of the Midwest:

Poison Hemlock (Conium maculatum)

• Toxic Part: Entire plant

• Risk: Extremely toxic to all livestock; fatal in small doses

• ID Tips: Fern-like leaves, purple-spotted stems, umbrella-shaped white flowers

• Management: Avoid mowing during flowering to prevent seed spread

Wild Parsnip (Pastinaca sativa)

• Toxic Part: Sap

• Risk: Causes skin burns (phytophotodermatitis); potential photosensitivity in livestock

• ID Tips: Yellow flowers, celery-like leaves, hairy stems

• Management: Wear protection when handling; mow before seed set

St. Johnswort (Hypericum perforatum)

• Toxic Part: Entire plant

• Risk: Photosensitization in light-skinned animals; severe cases can cause blindness

• ID Tips: Yellow flowers with black dots, translucent-dotted leaves

• Management: Control in overgrazed, low-fertility pastures

Common Milkweed (Asclepias syriaca)

• Toxic Part: Leaves and stems

• Risk: Contains cardiac glycosides; can affect cattle and sheep

• ID Tips: Thick leaves, milky sap, pink flower clusters

• Management: Monitor forage availability to discourage consumption

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

• Toxic Part: Wilted leaves (Cherry); regrowth and frost-damaged tissue (Johnsongrass)

• Risk: Cyanide poisoning; rapidly fatal

• ID Tips: Shiny leaves, white blossoms (Cherry); tall, midribbed grass with purple panicles (Johnsongrass)

• Management: Avoid grazing after frost; restrict access to wilted debris

White Snakeroot (Ageratina altissima)

• Toxic Part: Entire plant

• Risk: Milk sickness in humans; toxic to cattle, horses, goats

• ID Tips: Triangular leaves with toothed edges, white flower clusters

• Management: Remove early from shaded pasture edges

Horsenettle (Solanum carolinense)

• Toxic Part: Berries and leaves

• Risk: Contains solanine; neurological and digestive harm

• ID Tips: Spiny stems, star-shaped purple flowers, yellow berries

• Management: Spot spray or remove physically

Cocklebur (Xanthium strumarium)

• Toxic Part: Seeds and seedlings

• Risk: Especially toxic to pigs, sheep, cattle; causes liver damage

• ID Tips: Sandpaper leaves, hooked burs, dark-spotted stems

• Management: Minimize overgrazing to limit seedling exposure

Nitrate Accumulators (Pigweed, Lambs Quarters, Thistles, Johnsongrass)

• Toxic Part: Entire plant

• Risk: Nitrate poisoning; prevents oxygen transport in blood

• Management: Test forage after drought or fertilization before grazing

Field Horsetail (Equisetum spp.)

• Toxic Part: Entire plant

• Risk: Contains thiaminase; neurological symptoms in horses

• ID Tips: Hollow, jointed stems; resembles bottlebrush

• Management: Improve drainage, restrict livestock access

Best Practices for Pasture Safety "The first step to weed management is proper identification," Gruss advises. When unsure, producers should consult local field specialists. Most livestock will avoid toxic plants when better forage is available, but eliminating toxic species and managing pasture health is key.

Use herbicides with care and always follow label restrictions for grazing intervals. Preventing overgrazing and maintaining thick, healthy pasture growth will help suppress opportunistic weeds.