08/12/2025
W**d management is an important part of being a horse owner. Even if it's not your land.
This week we will focus on St John's Wort.
This w**d is highly toxic to horses particularly those with white skin. It spreads like wildfire ๐ฅ so it's very important we remove it as soon as we see it.
Removal can be done manually by pulling it out and spraying with herbicide chemicals such as glyphosphate.
St. John's Wort (Hypericum perforatum) is toxic to horses, causing photosensitization (severe sunburn/skin irritation on light-colored areas) due to the toxin hypericin, leading to redness, swelling, and discomfort, especially with sun exposure; ingestion can also cause digestive upset, weight loss, and lethargy, requiring removal from pastures and prompt vet care. Horses usually avoid it, but it becomes a risk when other forage is scarce, and controlling the w**d and providing shade are crucial to prevent poisoning.
Dangers to Horses
Photosensitization: The main risk; hypericin in the plant causes extreme sensitivity to sunlight, leading to painful skin reactions (blisters, redness) on unpigmented (white) skin, often on the muzzle, legs, and belly.
Digestive Issues: Can cause loss of appetite, weight loss, dullness, and sometimes diarrhea or constipation.
Behavioral Changes: Horses may become lethargic, weak, and reluctant to move.
Identification & Risk
Appearance: Yellow flowers with five petals, often with black dots on edges; leaves have tiny translucent spots (oil glands) visible when held to light.
Risk Times: Most dangerous when young or when it dominates pastures, especially during dry spells when palatable feed is lacking.
Hay: The toxin remains potent in contaminated hay.
What to Do if Your Horse Eats It
Remove from Sun: Immediately move the horse to a shaded area or bring them indoors.
Call Your Vet: Consult a veterinarian for diagnosis and treatment plan.
Remove the W**d: Control and remove St. John's Wort from all horse pastures.
Prevention
Maintain healthy, competitive pastures to reduce w**d establishment.
Ensure horses have access to shade.
https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/193075/St-Johns-wort.pdf