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Species Abstracts of Highly Disruptive Exotic Plants

at Scotts Bluff National Monument

Cynoglossum officinale

Park: Scotts Bluff National Monument (SCBL)
Species: Cynoglossum officinale L.
Common Name: Hound's tongue, dog bur, gypsy flower
Urgency Ranking: High
Overall Ranking: 7
Significance of Impact: 53
A. Current impact: 21
B. Ability to be a pest: 32
Feasibility of Control: 36

Taxonomic Description:
Hound's tongue is an erect (30-120 cm) biennial or short-lived perennial forb with a thick, black, woody taproot. Initial growth is in the form of a basal rosette with a single flowering stem produced the second year. This stem is unbranched below the inflorescence and leafy throughout. Basal and lower cauline leaves are petiolate, elliptic to oblanceolate (15-20 cm long and 2-5 cm wide) and tapering at the base. Upper leaves are alternate, numerous, not reduced or larger, acute to obtuse, and sessile or clasping. All leaves are pubescent on upper and lower surfaces. Flowers are perfect and in racemosely arranged cymes axillary to the leaves or on terminating short branches, pedicellate, crowded at anthesis, less crowded in fruit. The calyx (4-6 mm long in flower, enlarging to 1 cm in fruit) consists of five sepals with triangular lobes fused in the shape of a star. The corolla is a dull reddish-purple with five lobes fused at the lower part into a cylindrical tube (5-6 mm long) and not exceeding the calyx. The throat of the corolla bears five hairy scales. Five stamens are inserted into the upper part of the tube. The pistil consists of a deeply lobed ovary and simple style. Fruit is indehiscent and consists of one to four nutlets. Nutlets (5-7 mm long) are brown or grayish brown, rounded-triangular, dorsally flattened, and covered with short, barbed prickles.

Hound's tongue is native to Eurasia and was introduced to North America as a contaminant of agricultural seed. It is now found over much of North America. It grows on rangeland, pastures, abandoned cropland, roadsides, and waste places. It is most abundant in areas with more than 10% bare ground. It colonizes easily and quickly forms dense monocultures on disturbed habitats. It can become established on rangelands and retard the reestablishment of valuable range species. It is one of the noxious weeds receiving control measures by the Forest Service in the Intermountain and Rocky Mountain Regions.

This plant possesses several features which contribute to its success as a weed. The prostrate rosette of the first year resists mowing and grazing. The rosette withstands drought stress enabling the plant to survive water deficits and delay flowering until conditions are favorable. Hound's tongue also produces a thick, deep tap-root that enables it to extract water and nutrients from the lower soil strata. Nutrient reserves of the tap-root acquired during the first year are sufficient for normal seed production the following year, even if the plants are completely defoliated early in the spring. The large nutrient reserves in seeds of hound's tongue allow rapid seedling root growth. This allows the plant to become well established before drier weather begins. Barbs on the seeds promote long-distance dispersal by becoming entangled in the hair of passing animals.

Hound's tongue is a biennial or short-lived perennial species reproducing by seed. It forms a rosette in the first year and usually flowers in the second year. Flowering occurs from May through July, and seeds mature from July through August. Although the fruit usually consists of four nutlets, an average of fewer than three has been reported. Most plants have one or two stems, although plants with up to eight stems have been reported with a single stem producing up to 300 seeds. Estimates of total seed produced per plant range from 50 to more than 2000. Nutlets remain attached to the parent plant for several months before falling to the ground, generally within a radius of 2 m from the parent plant.

Newly ripened seeds exhibit innate dormancy which is released by a period of vernalization. Most of the seed overwinters in the soil, although some may remain attached to the parent plant. Seed burial depth, ambient temperature and moisture, soil fertility, and light have been found to affect seed germination in hound's tongue. Maximum germination occurs at 1 cm soil depth; seeds buried 5 cm deep germinate but do not emerge. Seeds on the soil surface desiccate and do not germinate. Seed germination has been found to be stimulated by low (0-10°C, 12% soil moisture) and alternating (8.5/2.5°C) temperatures. Hound's tongue does not produce a large, persistent bank of buried seeds. Research has found that when buried in the soil, no seeds survived 1 year after burial. A persistent seed bank, however, may result from seeds overwintering on the parent plant. Seeds remaining on the parent plant throughout the winter cannot undergo chilling in a moist strata, and, thus, dormancy must be overcome the following year.

An intermediate number of populations of hound's tongue occur at Scotts Bluff National Monument (SCBL) combining to cover an area of 5 to 10 hectares. They are found on sites disturbed within the last 10 years. Populations are concentrated near the canal and in the bottom areas along the North Platte River. Several plants were also found in the northwest area of park. Hound's tongue has the potential to delay the establishment of native species in disturbed areas and poses a threat to the areas' primary resources. Also, it has a major negative visual impact on the vegetation of SCBL.

An important consideration in controlling hound's tongue is that seeds are readily dispersed and have the potential to remain viable for 2-3 years, if they remain on the parent plant. Also, prior to using any control it is important to determine if enough desirable plants are present to replace the controlled species. If desired vegetation is scare or absent control will be of little value.

Research indicates that mowing second-year plants during flowering dramatically reduces seed production. Sixty percent of plants cut 0-7 cm above ground failed to regrow. Seed production of the plants which resumed growth (16.5 cm average height compared to 75 cm for unclipped plants) declined to approximately 25 seeds per plant compared to 364 seeds per plant in the unclipped controls.

Many herbicides are not specific to hound's tongue or may not be specifically licensed for this use. It is important to read and follow all label directions. In Montana, research indicates that 2,4-D amine applied at a rate of 1.12 kg/ha applied in May controlled up to 97% of the first-year hound's tongue plants. Application at flowering controlled up to 77% of the second-year plants. It has also been found that seed production of second-year hound's tongue plants in Montana was most sensitive to 2,4-D applied when the bolted plants were 28 cm tall. Glean (chlorsulfuron) gave complete control when applied any time beginning with the rosette stage until the bolted plant had attained 28 cm in height. In British Columbia, Tordon (picloram), Glean (chlorsulfuron), and Banvel (dicamba) applied at rates of 0.56-1.68 kg/ha, 0.04 kg/ha, and 1.12 kg/ha, respectively, applied either in spring or fall provided excellent control of this weed.


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