Brassica spp (white mustard, yellow mustard, wild mustard, charlock, black mustard, indian mustard); Erysemum cheiranthoide (wormseed mustard); Raphanus raphanastrum (wild radish); Thlaspi arvense (fanweed, field pennycrest); Barbarea vulgari (yellow rocket, wintercrest).
These weeds rarely are eaten unless they are included in hay. Several toxins have been proposed and various syndromes have
been associated with Brassica ingestion. However, the only proven toxicity is related to toxic isothicyanates and subsequent thyroid disturbances. As a
result, possible clinical signs are variable, but most are related to digestive-tract irritation that causes repeated mild
colic. Most animals recover if they are removed from the source.
Hypericum: Hypericum perforatum (St. Johnswort, Klamath weed, goat weed, amber, goat's beard, Tipton weed, Eola weed, Pennyjohn, Raisin Rose, Herbjohn, Commock
— Photo 7).
Photo 7: Hypericum perforatum (St. John's wort) is an erect perennial introduced weed that grows up to 1 m tall. The woody
stem has opposite branches. Leaves are opposite, sessile and oblong (2 cm to 3 cm long) with small, translucent glands on
the bottom. Flowers are yellow and the petals may have black, glandular dots on the margins.
Fagopyrin: Fagopyrum saggitatum (buckwheat).
Furocoumarins and psoralens
Ammii majus (Bishopsweed), Cymopterus watsonii (spring parsley) Lomatium spp., Thamnosma texana and T. montana (Dutchman's breeches)
When mature, these plants are rarely eaten, but young plants are more palatable and when eaten cause toxicity. Because they
contain a primary photodynamic toxin (hypericum, fagopyrin, furocoumarins or psoralens), they induce photosensitization or
sunburn. This is seen clinically as skin redness (erythema), edema, blisters, crusting, sloughing and secondary bacterial
The eyes especially are sensitive. Animals develop severe keratitis and conjunctivitis that is seen as tearing and photophobia.
Animals will recover if the source is removed and they are allowed time to clear the toxin. Treatment should include protection
from sun and standard wound care for burned areas.
Vicia villosa (hairy vetch), V. lavenworthii (lavenworth vetch — Photo 8)
Photo 8: Vicia villosa (hairy vetch), V. lavenworthii (lavenworth vetch) are European legumes introduced for pasture improvement.
These vetches have become established as weeds, found in waste areas and along roadsides in much of North America. Hairy vetch
is a prostrate or climbing annual that can get up to 2 m long or tall. Leaves have 10 to 20 leaflets that are 2.5 cm long,
and there are tendrils at the leaf ends. Flowers are purple to red with 20 to 60 flowers on one side of the flowering spike.
The flowers form 2-to 3-cm seed pods that contain small, hard seeds.
Hairy vetch, an introduced European plant, grows across North America. It becomes a problem when animals are poisoned in late
spring and midsummer.
The toxin has not been identified and the development of disease is poorly understood.
Poisoning generally affects black animals (horses and cows) by introducing a multi-systemic granulomatous disease (most likely
an allergic or hypersensitivity disease).