Houndstongue is a biennial, poisonous herb native to Eurasia. The plant is a member of the Borage family, which includes more commonly known plants such as Virginia bluebells, forget-me-nots and the fiddlenecks. Houndstongue tends to be a nuisance weed rather than a noxious plant unless infestations grow to become large patches. The plant contains alkaloids that are especially toxic to cattle and horses. The plant rarely is eaten in the green state unless desirable forage is short; however, animals will eat the dried plant in hay. Fatal liver disease in horses has occurred following two weeks of feeding hay with as little as 6 percent houndstongue.
Houndstongue forms a rosette the first year of growth and bolts and flowers the second season. The leaves are oblong, very pubescent and rough, which resemble a hound's tongue. Flower clusters range in color from red to burgundy and produce three to four nutlets, which are flat and teardrop-shaped with a very hard seed coat and numerous barbs. Houndstongue reproduces only from seeds, but can spread great distances because of the barbs on the seeds which cling to clothing, machinery and animals. Plants are generally found along trails and wooded areas where animals may rub the seeds off their coats. Most infestations have been found in the understory of trees and brush; however, infestation can occur in open rangeland where cattle bed down.
Control in non-crop lands:
Prevention is the best method to keep houndstongue from invading new lands. Checking livestock, horses, tack, clothing and vehicles for seeds when moving from areas with houndstongue is the first line of defense. Identifying houndstongue plants in pasture and rangelands early and controlling the infestations by removing mature seed bearing plants by hand is very effective.
Chemical: Applying herbicides to rosettes is the most effective method to control houndstongue. 2, 4-D applied in the spring (late May to mid June) easily control the rosettes. Escort (metsulfuron) can be applied throughout the growing season to rosettes. Plateau (imazapic) will control houndstongue both pre- and post-emergence, but grass injury is likely.
Biocontrol: A root weevil, Mogulones cruiger, has been released in Canada. The insect has become well-established in Alberta and has greatly reduced the houndstongue infestation in that province. However, this biological control agent has not been approved yet or release in the U.S. Several other insects are being evaluated; however initial results re not nearly as promising as those of the root weevil.