The Story of Houndstongue

Houndstongue, a plant native to Western Europe to central Asia, is highly invasive in character outside of its native range. Present throughout much of North America and now a common rangeland, pasture, forestland and riparian area weed across Montana, houndstongue was likely first introduced as a contaminant in cereal seed.

Houndstongue spreads locally by seed attached to the hide, hooves and paws of wildlife, livestock and other domesticated animals as well as on just about anything associated with humans such as clothing, recreational equipment and modes of transportation.

Houndstongue infestations are often associated with disturbed sites such as trails, roadsides and logging areas. Accidental introductions occur when seeds disperse as contaminants of crop seeds or soil, are transported internationally in wool, fleece, and animal fur or attached to live introduced stock. Its presence reduces the availability of forage, is poisonous to livestock and wildlife if ingested in sufficient quantities and has been reported to cause dermatitis when handled.

Cynoglossum officinale is the accepted scientific name of the weed commonly referred to as houndstongue. No subspecies of officinale have been reported.

The genus Cynoglossum belongs to family Boraginaceae (Borage family). The common name houndstongue may be derived from the shape of the leaves or from the belief that a leaf worn in the shoe could ward off dog attacks.

A long history of folklore associates houndstongue with various medicinal and practical uses. Root extracts were said to cure fever, chest and respiratory ailments, eczema, acne, and hemorrhoids. The leaves were used as a mole repellent in gardens and for protection of stored vegetables and fruits from rodents and as an ingredient in an ointment that cures baldness.

Houndstongue is an herbaceous (i.e. non-woody) biennial or short–lived perennial plant that produces single or sometimes multiple erect hairy stems, generally ranging in height from eight to 30 inches, and has a thick taproot that can reach depths greater than three feet in one year. Its deep root system gives it a competitive advantage over grasses and other native or desirable vegetation, in particular under moisture stress conditions.

It has rough, hairy, leaves that are arranged alternately along the main stem of mature plants. Leaves are generally seven to 11 inches long, 0.75 – 2.75 inches wide and lanceolate to oblong in form, or shaped like a hound's tongue, with prominent veins.

The lower leaves that emerge as seedlings in spring to early summer have short petioles, or stalks, that attaches the leaf to the stem and are arranged in rosettes, a circular arrangement that sits near the soil.

The upper leaves clasp directly onto the stem. Leaf margins, or outer edges, are entire, or smooth, and both the leaf surfaces are covered with hairs.

The flowers are dull reddish-purple in color with five petals, and emerge from axils, or the area between the upper leaves and the stem. The inflorescence is a raceme, a flower arrangement in which individual flowers are attached vertically along the main stem, with the oldest flowers at the base opening first.

Houndstongue flowers are self-pollinating and seed production does not rely on insects or require pollen from other plants. Repeated flowering has been reported to occur in some houndstongue plants in the second, third and even fourth year. In the majority of cases, however, plants die after flowering once.

Houndstongue plants produce seed clusters that consist of three or four nutlets, or small fruits, similar to a nut. A mature houndstongue plant can produce 2000-4000 seeds.

Fruits are indehiscent, not opening at maturity in a pre-defined way, and dependent on predation or decay to open. The seed coat is dark brown to black with a white embryo inside, and have a barbed, spiny husk.

Seedlings emerge in both spring and fall, and the rosettes bolt, or produce the flowering stems from which seeds are produced, in the second year.

Nutlets remain attached to the mother plant after maturation for up to three years or more. Seeds attached to the mother plant can remain viable for two to three years, whereas buried seeds rarely retain the ability to germinate for more than one year.

Seeds do not disperse long distances naturally unless attached to animal fur or another vector. Approximately 75 percent fall to the ground within a four-foot diameter surrounding mother plants.

Houndstongue seeds exert an allelopathic influence on neighboring species. Decoated seeds release a substance that significantly inhibits seed germination, seedling growth and root elongation of several grass and broadleaf plant species but does not affect houndstongue itself.

Research into biological methods of control of houndstongue has included testing of several insects as well as fungal pathogens. The root weevil Mogulones cruciger (released in Canada in 1997) and the flea beetle Longitarsus quadriguttatus (released in Canada in 1998) are well established in British Columbia and Alberta. The root-mining weevil released and utilized in Canada as a biological control agent has been shown to be effective but is not approved for release in the U.S. because it feeds on native species in the same plant family as houndstongue. The weevil has spread and is present in Montana but intentionally moving it to new locations may result in severe penalties. Research is currently being conducted in both Canada and the U.S. on other Mogulones weevil species that may not impact native Borage family species.

Control by hand pulling, digging or tillage may be practical for small houndstongue populations and an effective preventative measure on new infestations prior to seed formation. At least one to two inches of the taproot must be severed below the soil surface. Removing foliage by mowing, cutting or other means is not effective, as taproots often store enough nutrients for flowers and seed production to continue.

Herbicides including metsufuron (Escort or Cimarron), chlorsulfuron (Telar) and 2,4-D can be used to manage houndstongue. Application rates, application timing, grazing and harvesting restrictions and safety information are listed on the herbicide labels that accompany each product.

In general, spring treatments provide better control than fall, as well as application at the rosette growth stage. Due to the hairy nature of houndstongue leaves, adding a surfactant to the herbicide tank mix to increase plant penetration and uptake is recommended.

Houndstongue may be confused with blueweed (Echium vulgare) but the latter is separable by its narrow, more distinctly hairy rosette leaves and conspicuous blue flowers rather than reddish-purple. It may also be confused with common mullein (Verbascum thapsus) though this species has rosette leaves that are more hairy and have less conspicuous venation than the rosette leaves of houndstongue.

While short-term management of houndstongue infestations may be challenging, correct identification, an understanding of its life cycle and a working knowledge of effective treatment strategies will increase suppression. This will reduce potential negative impacts on producers, recreationalists and human and animal heath in the long run.