Poisonous Plants for Horses: Identification, Signs & Prevention
A barn-tested guide to the worst offenders, how to spot them, what signs to watch, how to lock down your pasture and hay, and exactly what to do if your horse gets into trouble.
Identification by Region & Season
Use these quick IDs as a field checklist. Add photos on your blog build (use the alt text ideas above) to create a visual guide for riders.
Red Maple (wilted leaves)
NE/Mid-Atlantic • Late summer–fall (wilted leaves)Leaf: 3–5 lobes, reddish petioles; wilted brownish leaves are highest risk.
Seeds: Paired samaras (“helicopters”).
Signs: Dark urine, lethargy (hemolysis).
Yew (Taxus spp.)
Landscaping near barns • Year-roundLeaf: Flat, dark-green needles; red arils (fleshy “berries”).
Signs: Sudden collapse, cardiac issues—extreme emergency.
Oleander
South/West landscaping • Year-roundLeaf: Long, leathery; Flower: white/pink/red clusters.
Signs: Cardiac arrhythmias, colic, weakness.
Ragwort / Groundsel
PNW/Northern states • Summer (also in hay)Flower: Yellow daisy-like; finely lobed leaves.
Signs: Weight loss, photosensitivity (liver damage).
Alsike Clover
Cool, moist pastures • Late spring–summer (in hay too)Flower: Pale pinkish heads; leaves lack watermark of white clover.
Signs: “Big liver” photosensitization, slobbers, oral irritation.
Water Hemlock
Wet areas/ditches • Late spring–summerStem: Hollow, often purple-streaked; Flower: white umbrella umbels.
Signs: Tremors, seizures—fatal fast.
Poison Hemlock
Roadsides/fields • Spring–summerLeaf: Fern-like; Stem: purple blotches; mousey odor.
Signs: Salivation, ataxia, respiratory distress.
Johnsongrass / Sorghum / Sudan
Many regions • Late summer–drought stressSeedhead: Open panicles; Leaves: midrib prominent.
Risk: Cyanogenic glycosides → sudden respiratory signs.
Bracken Fern
Wood edges • Spring–fall (and in hay)Leaf: Triangular fronds; Signs: Thiamine deficiency → neuro signs, weight loss.
Nightshade (Solanum)
Fencerows • Summer–fallFlower: Starry purple/white with yellow center; Fruit: green→black berries.
Signs: GI pain, depression, neuro signs.
Perilla Mint
SE/Midwest • Late summer–fallLeaf: Purple-tinged, serrated; square stems; mint smell.
Risk: Respiratory distress (toxic ketones).
Hoary Alyssum
Upper Midwest • Summer–fall (in hay)Flower: Small white; Seed: flat pods; greyish foliage.
Signs: Limb edema, fever, laminitis risk.
Black Walnut (shavings)
Bedding contaminant • Any timeID: Dark heartwood; juglone in shavings.
Signs: Sudden laminitis when used as bedding.
Tip Plants change appearance across growth stages. Re-ID at seed-head and after frost—risk often rises with stress, wilting, or in baled hay.
Clinical Signs & When to Call the Vet
- GI: drooling, mouth ulcers, colic, diarrhea/constipation, decreased appetite
- Neuro: depression, ataxia, tremors, seizures, abnormal behavior
- Cardiac/respiratory: weakness, arrhythmias, rapid breathing, collapse
- Photosensitivity: sunburn-like lesions on white/pink skin (muzzle, pasterns)
- Emergency now: suspected yew/oleander/water-hemlock ingestion; sudden collapse; severe neuro signs; dark urine; uncontrolled colic
Vet First Call your veterinarian immediately. Early intervention saves lives and reduces long-term damage.
Prevention: Pasture, Hay & Hygiene
Pasture Program
- Walk fields weekly—flag and remove weeds (roots and all) before seed set
- Rotate grazing to avoid overgrazing; rest and reseed bare spots
- Mow/brush-hog before seed heads mature; dispose of pulled plants safely
- Fence off high-risk zones (wet ditches, wood edges) during peak seasons
Hay Sourcing & Storage
- Buy from reputable growers; ask about weed control and cutting timing
- Crack open random bales—look for plant diversity and odd odors/discoloration
- Store dry, off the ground, with airflow; first-in, first-out rotation
Hygiene & Insect Pressure
- Keep feed/tack zones clean. Use SuperClean™ Stall & Trailer Cleaner as part of routine wash-downs to cut organic build-up around feeders and walls.
- Reduce biting insects that aggravate plant-related skin issues and nuisance pressure: Citraquin® 32oz and the full Citraquin® collection—see the How-To Guide for application patterns.
Repellents and cleaners do not neutralize plant toxins; they support a cleaner, lower-stress environment as you manage pasture & hay correctly.
Emergency Protocols (If Ingestion Is Suspected)
- Remove access—pull the horse from the area; fence or stall off the source.
- Collect evidence—take clear photos and a small plant sample in a bag (and note where found).
- Call your veterinarian immediately for instructions; provide weight, time since exposure, and signs.
- Do not force exercise, induce vomiting, or administer oils/meds unless directed.
- Offer water and keep the horse calm, shaded, and monitored pending care.
- Save hay tags/lot info if contamination may be from a bale—others may be at risk.
Aftercare For photosensitization-related dermatitis, stable during peak sun, use fly gear, and protect recovering skin per your vet’s plan (see product tie-ins below).
Product Tie-Ins (Real-World Use)
Reduce Insect Pressure
Citraquin® Environmental Defense Spray — 32oz • Natural, water-based spray riders use against flies, mosquitoes, and ticks as part of a layered program. See the How-To Guide.
Clean feed and wall surfaces regularly with SuperClean™ Stall & Trailer Cleaner to reduce grime that draws pests.
Skin/Hoof Support During Recovery
- Rapid Relief Restorative Cream—thin, water-resistant barrier for intact skin around healed areas, per veterinary approval.
- Silver Hoof EQ Therapy®—supports hoof bulbs/coronary band moisture when skin near the hoof is recovering; do not apply inside open wounds.
These products don’t treat poisoning—they help protect skin/hoof environments while your vet addresses the medical issue.
Poisonous Plants — FAQ
Do horses “know” not to eat toxic plants?
Not reliably. Hunger, boredom, overgrazing, or curiosity can override instincts—especially when plants are baled in hay or wilted (which can increase palatability and risk).
Is mowing enough to control weeds?
Mowing helps before seed heads mature, but many species regrow from roots. Uproot, spot-treat, or fence off stubborn patches and re-seed bare areas to outcompete weeds.
What about photosensitization?
Some plants cause primary photosensitization (e.g., St. John’s wort). Others damage the liver (e.g., ragwort), leading to secondary photosensitization. Stable during peak sun and work with your vet on liver support and skin protection.
Can toxic plants be in “good” hay?
Yes. Inspect random bales from every lot. Keep supplier info, harvest dates, and lot numbers so you can trace problems fast.
Educational note: This article provides general information and is not a substitute for veterinary diagnosis or treatment. Always follow your veterinarian’s guidance for suspected poisoning and skin recovery.
