Complete Guide to Texas Toxic Plants

Knowing the Plants That Can Kill Your Cattle

Texas rangelands are home to hundreds of plant species. Most make excellent forage, but dozens are toxic to cattle. Plant poisoning is a major cause of livestock death in Texas, with losses running into the millions of dollars every year. Knowing which plants pose the biggest threats, when they're most dangerous, and how to manage them can protect your herd and your bottom line.

This guide covers the most important toxic plants found on Texas ranches, their identification, toxicity levels, and prevention strategies.

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Understanding Plant Poisoning in Cattle

Why Do Cattle Eat Toxic Plants?

Cattle don't instinctively avoid all poisonous plants. They may consume toxic species when:

• Overgrazing - Good forage is depleted, forcing consumption of less palatable plants
• Drought conditions - Toxic plants may remain green when grasses dry
• Early spring - Toxic plants often emerge before preferred forages
• Hay contamination - Dried toxic plants in hay lose bitter taste but retain toxicity
• Curiosity - Young or newly introduced cattle may sample unfamiliar plants
• Increased palatability - Some plants become more palatable after frost or herbicide application
• Hunger - Stressed, hungry cattle are less selective

Types of Plant Toxins

The Top 20 Toxic Plants in Texas

Tier 1: Most Dangerous (High Toxicity, Common)

#### 1. Locoweed (Astragalus and Oxytropis species)

• Compound leaves with small leaflets
• Purple, white, or cream-colored pea-like flowers
• Distinctive inflated seed pods
• Weight loss despite eating
• Staggering, high-stepping gait ("locoism")
• Visual impairment
• Difficulty swallowing
• Abortion in pregnant cows
• Permanent brain damage with prolonged consumption
• Herbicide control (picloram, tebuthiuron)
• Biological control with locoweed weevil in some areas
• Maintain adequate forage to reduce consumption

#### 2. Oak (Quercus species) - Buds, Leaves, and Acorns

• Acorns with distinctive caps
• Most problematic: shinoak, blackjack oak, post oak
• Dark, tarry feces
• Reduced urination, then no urination
• Dehydration
• Kidney failure
• Death within 3-10 days of heavy consumption
• Supplement with high-quality hay during high-risk periods
• Calcium hydroxide (hydrated lime) at 10% of diet may reduce absorption
• Maintain stocking rates that ensure adequate grass

#### 3. Nightshade (Solanum species)

• Buffalo bur: spiny stems and leaves, yellow flowers
• Black nightshade: oval leaves, white flowers, black berries
• Diarrhea
• Weakness
• Difficulty breathing
• Paralysis
• Sudden death with large doses
• Avoid overgrazing
• Most common in disturbed areas—reduce soil disturbance
• Don't include contaminated hay

#### 4. Oleander (Nerium oleander)

• Leathery, narrow leaves in groups of three
• Showy pink, white, or red flowers
• Found near homes, abandoned homesteads, roadsides
• Colic
• Bloody diarrhea
• Cold extremities
• Trembling
• Sudden death, often within 8-24 hours
• Never dump yard waste in pastures
• Fence around existing oleanders
• Alert neighbors to danger

#### 5. Jimsonweed (Datura stramonium)

• Large, trumpet-shaped white or purple flowers
• Spiny, golf ball-sized seed pods
• Strong, unpleasant odor
• Dilated pupils
• Dry mouth
• Restlessness, then depression
• Constipation
• Difficulty swallowing
• Bizarre behavior
• Death from respiratory failure
• Herbicide control (2,4-D, dicamba)
• Avoid contaminating hay fields
• Most common in disturbed soils

Tier 2: Significant Danger (Moderate-High Toxicity)

#### 6. Cocklebur (Xanthium strumarium)

• Distinctive spiny burs
• Two-leaf seedling stage most toxic
• Depression
• Nausea, vomiting attempts
• Spasms and convulsions
• Death within 24 hours
• Mow or spray before maturity
• Fence off low areas after flooding

#### 7. Pigweed/Carelessweed (Amaranthus species)

• Alternate leaves
• Dense, bristly flower spikes
• Very common in disturbed areas
• Chocolate-brown blood
• Weakness
• Staggering
• Sudden death
• Abortion in pregnant cows
• Don't graze stressed pigweed stands
• Wait 7-10 days after frost before grazing
• Control with herbicides before stress occurs

#### 8. Perilla Mint (Perilla frutescens)

• Square stems
• Opposite, serrated leaves with minty smell
• Purple or white flower spikes
• Often found in shaded areas
• Open-mouth breathing
• Grunting
• Frothy fluid from nose
• Death within 1-3 days
• Mow before flowering
• Herbicide control (2,4-D)
• No effective treatment once symptoms appear

#### 9. Sorghum and Sudan Grass (Sorghum species)

• Includes grain sorghum, sudan grass, and johnsongrass hybrids
• Regrowth after cutting or grazing
• Drought-stressed plants
• 3-5 days after frost
• New growth after rain following drought
• Difficult breathing
• Bright red blood (early), then cherry-red mucous membranes
• Convulsions
• Death within minutes
• Wait 7-10 days after frost
• Avoid grazing during drought stress
• Test before grazing if concerned
• Ensiling reduces (but doesn't eliminate) toxicity

#### 10. Bitterweed/Bitter Rubberweed (Hymenoxys odorata)

• Narrow, finely divided leaves
• Yellow daisy-like flowers
• Strong bitter smell
• Very common in overgrazed pastures
• Green-stained muzzle
• Bloat
• Frothing at mouth
• Death in severe cases
• Provide supplemental feed during high-risk periods
• Herbicide application (2,4-D) when plants are small
• Good range management is best prevention

Tier 3: Localized or Seasonal Threats

#### 11. Water Hemlock (Cicuta maculata)

• Compound leaves with sharply toothed leaflets
• Small white flowers in umbrella-shaped clusters
• Chambered root with yellow oil
• Careful eradication (entire plant must be removed)
• Do not leave pulled plants where cattle can access

#### 12. Milkweed (Asclepias species)

• Pink, orange, or white flower clusters
• Distinctive pods with silky-haired seeds
• Labored breathing
• Rapid, weak pulse
• Dilated pupils
• Bloat
• Check hay for contamination
• Herbicide control where dense

#### 13. Texas Mountain Laurel (Sophora secundiflora)

• Compound leaves with glossy leaflets
• Purple, fragrant flower clusters
• Red seeds in thick pods
• Remove fallen pods during drought
• Generally not consumed unless forced

#### 14. Threadleaf Groundsel (Senecio longilobus)

• Thread-like leaves
• Yellow daisy flowers
• Common in West Texas
• Wandering, circling
• Pressing head against objects
• Jaundice
• Death weeks to months after consumption
• Maintain good forage availability
• Animals may consume small amounts over months before showing signs

#### 15. Rayless Goldenrod (Isocoma pluriflora)

• Narrow, sticky leaves
• Yellow flower clusters lacking ray flowers
• West Texas and Trans-Pecos region
• Weakness
• Difficulty swallowing
• Death from heart failure
• Provide supplemental feed
• Toxin passes into milk (historical cause of "milk sickness" in humans)

Additional Notable Toxic Plants

Seasonal Risk Calendar

Spring (March - May)

• Oak bud and young leaf emergence
• Cocklebur seedlings after floods
• Larkspur emergence (where present)
• Nightshade new growth
• Limited grass forces consumption of toxic plants
• Ensure adequate forage or supplementation
• Restrict access to known problem areas
• Watch for locoweed addiction signs

Summer (June - August)

• Jimsonweed flowering
• Perilla mint approaching peak toxicity
• Nitrate accumulation in pigweed during drought
• Water hemlock in wet areas
• Sudan grass and sorghum if stressed
• Monitor for drought stress in susceptible species
• Fence wet areas with water hemlock
• Provide water to reduce consumption of toxic plants

Fall (September - November)

• Perilla mint at maximum toxicity
• Post-frost sorghum danger
• Post-frost nightshade palatability increases
• Rayless goldenrod consumption increases
• Monitor acorn consumption
• Provide supplemental feed during mast years
• Scout for perilla mint in shaded areas

Winter (December - February)

• Bitterweed on overgrazed pastures
• Oak consumption if browse is limited
• Hay contamination issues (year-round accumulation)
• Locoweed remains toxic under snow
• Prevent overgrazing
• Maintain body condition to reduce forced consumption
• Scout for bitterweed infestations

Prevention Strategies

Pasture Management

• Cattle rarely eat toxic plants when good forage is available
• Prevent overgrazing at all times
• Provide supplemental hay during drought
• Map locations of toxic plant populations
• Note when plants emerge and flower
• Track year-to-year changes
• Mechanical removal for small infestations
• Biological control where available
• Reseeding with desirable forages after control

New Cattle Precautions

• Native cattle often learn to avoid local toxic plants
• Introduced cattle may not recognize dangers
• Monitor new cattle closely for first season
• Avoid placing new cattle in high-risk pastures

Hay and Feed Safety

• Inspect hay for toxic plant contamination
• Purchase from reputable sources
• Store hay properly to maintain quality
• Never buy moldy or unknown-source hay

Responding to Suspected Poisoning

Immediate Actions

• Remove cattle from pasture - Prevent further consumption
• Identify the plant - Critical for treatment decisions
• Call your veterinarian - Specific treatments vary by toxin
• Document everything - Photos of plants, symptoms, affected animals
• Collect samples - Plant samples, rumen contents from dead animals

When to Call Emergency Vet

Call immediately if you observe:

• Multiple animals affected simultaneously
• Sudden death with no warning
• Severe respiratory distress
• Seizures or convulsions
• Muscle tremors after exertion
• Staggering in multiple animals

Information for Your Veterinarian

Prepare this information before calling:

• Number of animals affected
• Symptoms observed (be specific)
• Time symptoms were first noticed
• Recent pasture or feed changes
• Plants found in pasture
• Weather conditions (frost, drought, etc.)
• Pregnant animals affected?

Diagnostic Resources

Texas Veterinary Diagnostic Laboratories

• Branch: Amarillo, Center, Gonzales
• Website: tvmdl.tamu.edu
• Can analyze stomach contents and tissues

Extension Resources

• Texas A&M AgriLife Extension county offices
• Texas Parks & Wildlife plant identification
• USDA-NRCS plant identification resources

Smartphone Apps

• iNaturalist - Plant identification
• PlantNet - Photo-based identification
• Texas Invasives app - Includes many toxic species

Bottom Line

• Prevention beats treatment - Most toxic plant poisoning cases are preventable through good management
• Maintain adequate forage - Hungry cattle make poor choices
• Know your pastures - Scout regularly, especially in spring and fall
• Respond quickly - Early removal from toxic pasture improves survival
• Season matters - Same plant may be safe or deadly depending on conditions
• Young cattle and new arrivals are vulnerable - They lack learned avoidance
• Hay can kill - Dried toxic plants lose taste warnings but retain toxicity
• Document and learn - Each incident teaches you about your specific ranch

Related Resources

• Locoweed: Identification and Prevention
• Oak Poisoning in Cattle
• Nightshade Species on Texas Ranches
• Seasonal Poisoning Calendar
• Pasture Walk Inspection Guide

References

• Knight, A.P. & Walter, R.G. (2001). A Guide to Plant Poisoning of Animals in North America. Teton NewMedia.
• Texas A&M AgriLife Extension. (2024). "Toxic Plants of Texas."
• Burrows, G.E. & Tyrl, R.J. (2013). Toxic Plants of North America. Wiley-Blackwell.
• USDA Natural Resources Conservation Service. (2024). Plants Database - Texas.
• Texas Veterinary Medical Diagnostic Laboratory. (2024). "Plant Poisoning Submissions."
• Hart, C.R. et al. (2000). "Toxic Plants of Texas: Integrated Management Strategies." Texas A&M Publication B-6105.
• Ralphs, M.H. (2002). "Ecological Relationships Between Poisonous Plants and Rangeland Condition." Journal of Range Management.

"Knowing your plants is knowing your protection"