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March 2014

Invasive Watch: Houndstongue (Cynoglossum officinale)

Houndstongue is a biennial plant that measures from 8 to 48 inches tall. The plant’s first-year growth is strictly vegetative, and flowering occurs only in the second year. The first year, it forms a deep taproot and basal rosette. The dark-green basal leaves are oblong, very pubescent and rough, measuring between 6 and 8 inches long. The entire plant has soft, white hairs covering it.

A flowering stem develops in its second year, and leaves on the flowering stem are alternate, sessile and narrower toward the top of the plant. Houndstongue flowers typically bloom in June and July, and they are reddish-purple with a five-lobed corolla, producing four triangular, rounded seeds. Seeds are small, brown and about one-third of an inch in length, and contain barbs on the nutlets that easily attach to animals vehicles and humans, enabling them to spread and reproduce over long distances. Each plant is capable of producing up to 2,000 seeds a year before it dies after the second year.

Where It's Found
Houndstongue is native to Eurasia and prefers well-drained, relatively sandy and/or gravelly soils such as are found in riparian zones, coastlands, grasslands and along roadsides and agricultural areas. It’s considered toxic to grazing animals and has been reported as invasive in seven western U.S. states, including California, Washington and Wyoming. Once established, houndstongue quickly forms dense monocultures.

How to Treat It
To effectively treat houndstongue, apply Opensight® specialty herbicide at 2.5 to 3.3 ounces per acre to rosettes. As plant bolts, increase the rate to 3 to 3.3 ounces up to early bud stage. Add 1 quart of 2,4-D if treating after bud stage for greater control.