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Houndstongue identification and control: Cynoglossum officinale

Houndstongue identification and control

Cynoglossum officinale, Boraginaeae Family

Houndstongue - Cynoglossum officinale - Click for larger image

Houndstongue is a toxic biennial plant introduced from Europe, likely as a contaminant in cereal seed. Like other members of the Borage family, houndstongue is rough in texture and produces flowers in long, coiled stalks. In addition to poisoning animals who ingest it, houndstongue also produces prolific amounts of irritating bur-like seeds that cling to animals and clothing like Velcro.

Houndstongue is found throughout the United States and Canada and is considered a noxious weed in many western states. In King County, Washington, houndstongue is only present in a few locations, so we are actively looking for it and working to eradicate it where we find it.

Legal status in King County, Washington

Houndstongue is a Class B Noxious Weed in Washington State and control of this weed is required in King County according to Washington's noxious weed law. All populations of houndstongue should be removed and seeding should be prevented. For more information, see Noxious weed lists and laws.

Identification (see below for more photos)

    Houndstongue - Cynoglossum officinale - click for larger image
  • Biennial in the Borage family
  • First year plants form a rosette of long, rough, hairy, tongue-shaped leaves
  • Second year plants are 1 to 4 feet tall with stout, upright stems, usually branched above
  • Entire plant covered with long, soft hairs
  • Plants have several narrow flower clusters, slightly coiled
  • Flowers dull reddish-purple, drooping slightly along slender stalks, about 1/3 inch wide
  • Leaves alternate, long and narrow, smaller higher up the stem, 1 to 3 inches wide, rough, hairy, lacking teeth and lobes, with distinctive veins
  • Lower leaves up to a foot long and resemble a hound's tongue, broader at the tips and tapering to a petiole (leaf stalk) at the base; upper leaves are reduced, narrower, and lack petioles (stalks)
  • Plants have a thick, black, woody taproot that can reach 3 feet deep
  • Houndstongue - Cynoglossum officinale - click for larger image
    Each flower produces four nutlets (seeds), about 1/3 inch long, that break apart at maturity and cling to clothing and animals
  • Nutlets are brown to grayish-brown, rounded triangular in shape, and covered with short, hooked bristles

Habitat and impact

Usually found in pastures, along roadsides, forest rangelands, abandoned fields and disturbed habitats. It is uncommon west of the Cascades, but widespread in the interior of Washington State and British Columbia. Houndstongue causes a loss of pasture and range for grazing animals, increases cattle marketing costs, and reduces fitness in livestock. In addition to being a nuisance to recreationists due to its bur-like seeds, houndstongue is toxic and has the potential to poison domestic animals and wildlife that might graze on this plant or eat it mixed in with hay. Plants become more palatable when dry or after herbicide treatment. Animals are most likely to consume houndstongue in contaminated hay.

Like tansy ragwort as well as other members of the Borage family such as viper's bugloss and comfrey, houndstongue contains toxic pyrrolizidine alkaloids, which cause liver cells to stop reproducing.

Houndstongue - Cynoglossum officinale - click for larger image

Animals may survive for six months or longer after they have consumed a lethal amount before succumbing. Sheep are more resistant to houndstongue poisoning than are cattle and horses. Horses may be especially affected when confined in a small infested area lacking good forage. Houndstongue remains toxic when dry, and cattle and horses have died in the U.S. from eating hay contaminated with houndstongue.

Symptoms are varied but may include digestive disturbances, restlessness, lack of coordination, convulsions and coma. Symptoms may develop anywhere from a few days to several weeks or months after animals have eaten the plants. Once symptoms are obvious, an animal may die within a few days. There is no specific treatment, just supportive treatment for the symptoms and removing the source of poisoning.

Houndstongue - Cynoglossum officinale - click for larger image

When livestock are exposed to houndstongue, the seeds attach to the animal. In addition to creating a nuisance by getting into wool and fur, the burs can become embedded in the eye or eyelids and cause eye damage in animals. This can increase the cost of raising livestock as well as reduce their overall health and value.

Houndstongue prefers forest sites and thrives especially well in forest openings cleared by logging operations and road construction. Houndstongue is shade-tolerant and not tolerant of drier grassland areas with less than 12 inches of annual rain. In regions with low rainfall, houndstongue tends to grow in wetter grasslands and moist draws. Most infestations are found on coarse, gravelly to sandy alkaline soils up to 9,000 feet elevation.

Growth and reproduction

Houndstongue - Cynoglossum officinale - click for larger image

Houndstongue is a biennial to short-lived perennial that spreads by seed. First year plants do not produce flowers. Second year plants produce a flowering stalk in May to July, go to seed and then usually die. Some plants may persist for a few years. Seeds are produced in 4-parted nutlets that break apart at maturity and disperse mostly by being carried on the fur of animals and other carriers such as clothing, machinery, and vehicles. Houndstongue produces more than 600 burs per plant, and up to 2,000 seeds. Over-grazing and disturbance further encourages the spread and growth of houndstongue.


Houndstongue - Cynoglossum officinale

Don't let houndstongue go to seed. Hand pull or dig up isolated plants and small patches and remove as much of the root as possible. If the soil doesn't allow for effective digging, spot treat with herbicide. Cutting second year plants, by conventional mowing if practical or with weed-eaters, reduces seed production and spread. If plants are cut close to the ground, many plants will not re-grow, although some will and may flower and seed later in the season or the following year. Do not mow plants that are already in seed as this will likely disperse the seeds and possibly get moved on the mowing equipment to un-infested sites.

In infested areas, it is important to re-seed disturbed or bare soil with a competitive species as soon as possible after disturbance to avoid it getting infested with houndstongue, or other weeds in the area. Clean burs from animals, clothing, shoes and equipment before leaving infested areas. Houndstongue does not withstand regular cultivation and is less competitive in areas with healthy grass cover.

For larger infestations, chemical control may be more cost-effective than manual removal. Adding a surfactant will improve results. Metsulfuron (Escort) at 1-2 ounces per acre is effective on houndstongue any time the plant is actively growing (but apply only to pasture, rangeland and non-crop sites). First year rosettes can be controlled with 2,4-D at 2 pints per acre in spring, but second year plants are not controlled well with 2,4-D. For more information or a site-specific recommendation in King County, Washington, contact the noxious weed program. For information in other locations, contact your local weed board or extension office or refer to the recommendations in the Pacific Northwest Weed Management Handbook. Whenever using an herbicide, carefully follow all directions given on the label and follow any local or state requirements for herbicide use at that location.

Additional information on houndstongue

What to do if you find this plant in King County, Washington

Please notify us if you see houndstongue growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because houndstongue is not established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as houndstongue in order to help us and others locate new infestations in time to control them.

Houndstongue photos

Houndstongue flowering stem
Houndstongue flowering stems
Houndstongue plant on I-90
Houndstongue on I-90
Houndstongue nutlets
Young houndstongue plant
Closeup of houndstongue nutlets
Young and old houndstongue
Last year's houndstongue
Houndstongue plant
Closeup of houndstongue stem

Report houndstongue in King County, Washington

Locate houndstongue in King County, Washington

Related information

Related agencies

Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).