Why is it Important to Identify Toxic Species?

Poisonous or toxic plants can pose an economic loss to livestock. Understanding the effects, identifying the threat, and effectively removing poisonous plants can offer the best success to warding off costly issues. Below you will find information on poisonous weed species that affect livestock and humans. Plants usually have different levels of toxicity during different stages of their growth, although some are toxic in all stages. Poisoning can have varied effects depending on the species and weight of the animals, along with the quantities and duration of consumption. Many species of thistle and other plants with spines, although not toxic, can cause sores in grazing animals' mouths, or eyes, causing discomfort, potential for infection, and loss of appetite. If you need any assistance in exterminating these pests please contact us.

Common Fiddleneck

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Mostly toxic to cows and horses. Sheep, goats, and chickens have lesser reactions to this species.

☢️ Toxin: Pyrrolizidine Alkaloids.

Symptoms include: neurological symptoms, liver disease, wandering disease, hard liver disease, protein poisoning. Most commonly poisonings occur when contaminated hay is fed over the course of days to months.

Yellow Starthistle

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Horses are mainly affected.

☢️ The exact toxin is unknown.

Symptoms include: Nigropallidal Encephalomalacia or chewing disease, fatigue, tongue flicking, involuntary chewing movements, inability to eat or drink, leading to eventual starvation or dehydration. It affects the part of the brain that controls fine motor movements. Effects are cumulative, horses must consume 50-150% of the animal's weight in dry matter over the course of 1-3 months to see effects.

Purple Cudweed

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Under stressful conditions this plant can develop an excess of nitrates, this can be lethally toxic to cattle.

☢️ Toxin: Nitrates.

Symptoms of nitrate poisoning include: muscle tremors, weakness, and frequent urination. Conditions that induce nitrate production include: mowing down, herbicide that stunts but does not kill the plant, drought, or overly saturated soil.

Creeping Woodsorrel & Buttercup Oxalis

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Under stressful conditions this plant can develop an excess of nitrates, this can be lethally toxic to cattle.

☢️ Toxin: Nitrates.

Symptoms of nitrate poisoning include: muscle tremors, weakness, and frequent urination. Conditions that induce nitrate production include: mowing down, herbicide that stunts but does not kill the plant, drought, or overly saturated soil.

Buttercup Oxalis

Creeping Woodsorrel

Creeping Woodsorrel

Buttercup Oxalis

Other species that are toxic, but less common in the Central Valley:

• Buttercup

• Chokecherry

• Horsetail

• Western Hemlock

• Big Periwinkle

• Russian Knapweed

• Common Crupina

• Houndstongue

• Heliotrope

• Fixweed

• Halogeton

• Western Brackenfern

• Castorbean

• Deathcamas

• Larkspur

• Roughseed Buttercup

• Cutleaf Groundcherry

• Horsenettle

• African Rue

• Field Horsetail

• Scouringrush

• Foxglove

Works Cited

• Doll, Jerry. “Do You Have Poisonous Weeds in Your Pastures and Forages?” Team Forage, fyi.extension.wisc.edu/forage/do-you-have-poisonous-weeds-in-your-pastures-and-forages/. Accessed 8 Dec. 2023.
• DiTomaso, Joseph  M., and Evelyn  A Healy. Weeds of California and Other Western States. Univ. of California, 2007.
• “Oxalis Corniculata.” Oxalis Corniculata (Creeping Woodsorrel) | North Carolina Extension Gardener Plant Toolbox, plants.ces.ncsu.edu/plants/oxalis-corniculata/. Accessed 8 Dec. 2023.