Locoweed, also known as “loco” or “crazyweed,” encompasses various Astragalus and Oxytropis species. These plants challenge land managers and gardeners, impacting healthy ecosystems and gardens.
Understanding Locoweed
Locoweed, part of the pea family (Fabaceae), includes hundreds of Astragalus and Oxytropis species. Its name comes from the Spanish “loco” (crazy), referencing neurological effects on animals that consume it. Only a subset of these species produce the “locoism” toxins.
Typically perennial herbs, some annual locoweed species grow in tufts or clumps 8 to 30 centimeters high. They thrive in semi-arid regions, foothills, plains, and disturbed soils, adapting to various environments. Their early spring emergence, when other forage is scarce, contributes to their spread.
Identifying Locoweed in Your Garden
Locoweed in your garden has distinct features. Its leaves are typically pinnately compound, with leaflets arranged along a central stem, creating a feather-like appearance. Leaf hairiness varies from smooth to densely covered in silvery hairs.
Locoweed flowers are pea-like, displaying white, purple, yellow, or pink. Each flower has a top petal (banner), two side petals, and a keel. A key difference between the two genera is the keel: Oxytropis species have a pointed keel, while Astragalus species have a blunt one. After flowering, plants produce legume pods of various shapes, often containing numerous seeds.
The Dangers of Locoweed
Locoweed’s danger comes from swainsonine, an indolizidine alkaloid. This toxin, produced by a fungal endophyte within the plant, passes through its seeds. Swainsonine inhibits enzymes, disrupting cellular function and causing sugar accumulation.
Livestock (horses, cattle, sheep, goats) are susceptible to locoweed poisoning, with symptoms appearing after weeks of continuous ingestion. Affected animals may show neurological damage like depression, lethargy, irregular gait, tremors, and erratic behavior. Other effects include weight loss, reproductive issues, and congestive heart failure. Domestic pets and humans are also at risk; protective clothing is advised when handling the plant.
Managing and Removing Locoweed
Managing locoweed in a garden requires persistent effort. For smaller infestations, manual removal is effective. Hand-pulling or digging ensures the entire plant, including its root system and seeds, is removed. This is best done when soil is moist, making extraction easier and preventing resprouting from root fragments.
Mechanical control, like mowing, can prevent seed production, especially at full bloom. However, mowing may not be effective for all perennial species with deep taproots. Chemical control is another option, with broadleaf herbicides like picloram plus 2,4-D, metsulfuron, and clopyralid proving effective. Herbicides work best when applied in spring during the vegetative or early bloom stage, on healthy, actively growing plants, and under suitable weather conditions. Always adhere to product label instructions.
Preventing Locoweed Infestations
Preventing locoweed infestations involves proactive measures. Improving soil health and fertility promotes desirable plant growth, which outcompetes locoweed for resources. Maintaining healthy, dense plant cover discourages locoweed establishment.
Regularly monitor your garden for new locoweed seedlings, especially in disturbed areas. Promptly remove young plants before they establish a strong root system or produce seeds. Preventing seed dispersal is key; locoweed seeds remain viable for 50 years or more, so clean gardening tools and avoid contaminated soil or hay to limit new introductions.