How to Kill Locoweed

Kill white locoweed with the herbicide spray picloram when the plant is young. Locoweed seeds can last as long as 50 years. Even after the plant is killed, it can reappear again years later. The type of locoweed known as woolly loco is harder to control, but picloram has been successful in controlling both of these species.

Spray metsulfuron on locoweed to kill and control it. metsulfuron can be applied aerially or through a ground spray method; use at least of 0.375 oz a.i. (active ingredient) per acre. This herbicide is good for all broadleaved weeds, (those that produce through seed), and won't harm other grasses.

Control locoweed with the herbicide clopyralid by applying it when the plants are young. Be sure this herbicide is approved for use in your area and that you follow the manufacturer's instructions. Move your livestock to another area where there isn't much locoweed before you spray, and move them back only after it and all traces of the insecticide are gone.

Cultivate the native insect known as cleonidius trivittatus, a root-feeding weevil. The insect is known to ranchers, and has lately been found in higher numbers throughout New Mexico. The insect larvae feed on the inside and outside of locoweeds, cutting off the roots; they're effective in killing woolly loco, but they don't attack white locoweed. A caterpillar called walshia miscolorella invades both white and woolly loco, but rarely kills the plants unless they are stressed in some other way, such as from drought

Wait for the right kind of weather before you apply any herbicide to locoweed, as this will make a difference in the herbicides effect. Don't apply any insecticide to locoweed when the soil temperature is less than 55 F at a depth of 6 inches, or if the soil is too dry. Herbicides will also have less effect if insects are attacking the plant or just before a rain, as this will wash most of the herbicide off of the plant.