Managing Houndstongue in Natural Areas


(Cynoglossum officinale) 


Houndstongue is a biennial or short-lived perennial plant that was introduced to North America in contaminated cereal grain. It is found throughout the southern Canadian provinces and all but seven states in the U.S.

Houndstongue forms a rosette in its first year of growth and produces a stem, flowers, and seeds during the second growing season. The majority of houndstongue plants die after producing seed; however, some plants regrow for several years.

The rosette leaves resemble a hound’s tongue and emerge from a thick, dark, woody taproot. Flowers are reddish-purple and produced on stalks that can be up to four feet tall (Photo).

Houndstongue seed spreads long distance by barbs, which attach to clothing, shoes, and fur/hair on domestic animals and wildlife (Photo inset). Individual plants produce up to 2000 seeds. Houndstongue contains an alkaloid that is toxic to grazing animals, especially cattle and horses, and is most problematic in contaminated hay.


Houndstongue often grows in a complex with other weeds, such as spotted knapweed and Canada thistle. Growth regulator herbicides, such as Milestone® herbicide (aminopyralid), provide excellent control of knapweed and thistle, but have less activity on weeds such as houndstongue. In contrast, metsulfuron-methyl provides good control of houndstongue, but poor control of knapweed and thistle. Application of Opensight® herbicide, which combines aminopyralid and metsulfuron-methyl in a dry, water-dispersible granule formulation, effectively controls a complex of houndstongue, knapweed, thistle and many other broadleaf weeds with one application.

Apply Opensight at 2.5 ounces of product per acre (oz/A) to houndstongue rosettes in spring, increasing the application rate to 3.3 oz/A at bolting to early-bud growth stage. Add 1 quart of 2,4-D to Opensight at 3.3 oz/A after the bud stage, to reduce flowering and seed production.

Individual houndstongue plants can be controlled by digging or hand pulling. The upper two to three inches of the taproot must be removed to stop the plant from re-growing from the root crown.

Research on biological control of houndstongue is ongoing through efforts at University of Idaho and the Centre for Agriculture and Biosciences International (CABI) in Switzerland.


Published September 2017; Revised June 2019

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Milestone and Opensight are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details.

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