Common Names

The loco weed or stemless locoweed is known among stockmen as crazy weed, rattleweed, loco-vetch, and white loco.

Loco Weed

- Plate XXIII


It is a low silky-haired perennial with tufts of very short stems rising from a thick woody rootstock. The stems are so short that the plant is often described as stemless. The leaves are four to nine inches long, pinnately compound with nine to nineteen leaflets which are longer than wide and pointed. The flower stalks are longer than the leaves, the flowers, half to three-quarters of an inch long, vary in colour from purple and violet to yellow or yellowish-white; they are arranged in dense heads. The seed pods are incompletely two-celled, firm, leathery, and covered with silky hairs. The plants vary greatly as regards hairiness, size, and shape of leaflets, colour of flowers and size of pods. The plant is in bloom from April to August or later, according to locality.


The loco weed is common on prairies and dry plains from Saskatchewan to British Columbia and the Yukon.

Poisonous Properties

The toxic principles of the loco weed have not yet been determined, but its poisonous action upon animals has been fully established in Canada and the United States by field observations.

Animals Affected

Horses, cattle, and sheep may all form what is known as the loco-habit, and succumb sooner or later to its poisonous action. The greatest losses, however, in Western Canada have occurred chiefly among cattle. The world "loco" meaning "crazy", is derived from the Spanish, and is applied in reference to the peculiarities of movement shown by the affected animals.


The general symptoms of poisoning are awkwardness, trembling, loss of control of muscular movement, impaired eyesight and hearing. In extreme cases the animal becomes blind, loses all power of locomotion, refuses food, except loco weed, and dies usually in convulsive spasms.

E. A. Watson (Report Veterinary Director General, Ottawa, 1909) describes the effect upon horses as follows: "Mental derangement and inco-ordinate muscular action form the most constant and characteristic symptoms of the disease. The peculiar gait is at once remarked upon, locomotion being performed slowly and with deliberation, accompanied by overflexion and extension of the limbs. The head is carried low, the arm lifted high, so that the knee and chin are nearly horizontal and in close proximity. The animal appears to be walking over invisible obstacles, and if driven fast will frequently stumble and fall, though the ground be perfectly level. When the condition is very severe, it is almost impossible to force him out of a slow walk; if urged he becomes excited, moving the limbs up and down upon the same spot, "marking time" as it were, or moving forward only a few inches at a step. Visual errors are common. The loss of the sense of direction is well marked. When it is attempted to drive an animal in a particular direction he will tread in semi-circles and run into wire fences or gates. An animal is sometimes unable to locate a dish of oats placed before him, the attempts being often ludicrous."

Remedy and Means of Control: Give laxatives and supply good nutritious food. Strychnine has been recommended for cattle, and Fowler's solution for horses.

E. A. Watson says in regard to preventive measures: - " Very little can be advised in the way of medicinal treatment. But if the spread of the disease among healthy animals on a range where the grass and fodder conditions appear excellent can be accounted for by the loco habit largely acquired by imitation, it is obvious that affected animals should at once be removed from the healthy to a range or pasture free from the obnoxious weeds. Healthy animals on the range could be placed in charge of a herder and kept separate from locoed animals. Instances are reported where affected cattle, by early removal to a range free from loco plants, or taken and hand-fed, have so far recovered as to be profitably slaughtered, though such animals are always stunted and undersized."The loco-weed may be destroyed by cutting off the roots well below the crown, that is at least three inches below the surface of the soil. This should be done with a very heavy sharp and narrow steel hoe when the plants are in flower, or even before, to prevent the scattering of seeds. Plants that have been so cut off will not sprout again, but seeds already in the soil may germinate. By destroying the young plants before they reach maturity, the land will be freed from the weed in a season or two at far less cost than that caused by the death of live stock.

Symptoms 33