Marshall TrimbleWhat is locoweed?

Vic Perry

Moncton, New Brunswick, Canada

Locoweed comes from the Spanish word for crazy or mad. It is a toxic plant (of various types) that produces swainsonine, a phytotoxin harmful to livestock. It can come from any number of plants and is fairly widespread in the Western mountains. Blossoms on locoweed might be blue, purple, yellow or white. Livestock that eat the weed can become lethargic, emaciated and lose their sense of direction.

Marshall Trimble is Arizona’s official historian, board president of the Arizona Historical Society and vice president of the Wild West History Association. His latest book isArizona’s Outlaws and Lawmen; History Press, 2015.

If you have a question, write: Ask the Marshall, P.O. Box 8008, Cave Creek, AZ 85327 or e-mail him at

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