Dalmatian toadflax (Linaria
dalmatica (L.) P. Mill. ssp. dalmatica) FamilyFamily: Scrophulariaceae Description and VariationDescription and Variation: Dalmatian toadflax is an erect, short-lived, perennial herb, 0.8 to 1.5 m tall. The plant is hairless and glaucous, growing from a woody, branching base. The light green, waxy, alternate leaves are heart-shaped and clasp the stem. The flowers are bright yellow, tinged with orange, and resemble snapdragon flowers. The petals have two lips; the upper lip is two-lobed while the lower one is three-lobed. Individual flowers are nearly sessile, occurring in long, terminal racemes (USDA-ARS 1971; Morishita 1991). Economic ImportanceEconomic Importance: Beneficial - Because of its showy flowers, Dalmatian toadflax has been cultivated as an ornamental (Alex 1962). Detrimental - Mature Dalmatian toadflax plants are strongly competitive. Studies indicate that plots without Dalmatian toadflax may produce two and a half times as much grass as plots with toadflax (Robocker 1974). Mature plants are especially competitive with shallow-rooted perennials and winter annuals. Because of its competitive ability, Dalmatian toadflax is a concern in pasture and rangelands, as well as in natural areas, where it may outcompete more desirable, native species. Geographic DistributionGeographic Distribution: In its native habitat, Dalmatian toadflax occurs from the Dalmatian coast of the former Yugoslavia to Romania, Bulgaria, Albania, Greece, Crete, Turkey, Azerbaijan, Syria, Iran, and Iraq. Its Old World latitudinal range is roughly 35° N to 47° N. In North America, the species is known from at least 15 states and six Canadian provinces, with a latitudinal range of 35° N to 56° N (Alex 1962). HabitatHabitat: In North America, Dalmatian toadflax occurs in a variety of habitats, including: roadsides, pastures, rangelands, and waste areas. It has spread most extensively west of the 100th meridian, occurring primarily on coarse-textured soils, ranging from sandy loams to coarse gravels (Alex 1962). History: Because of its showy flowers, Dalmatian toadflax has been cultivated since the 16th century and has subsequently become widely distributed throughout the world. Dalmatian toadflax was probably introduced to North America in the late 1800’s as an ornamental. The first records of the species in Washington date back to the 1920’s, when the species was collected near Spokane (1926) and Bingen (1927) (Alex 1962). Because of its showy flowers, Dalmatian toadflax has been cultivated since the 16th century and has subsequently become widely distributed throughout the world. Dalmatian toadflax was probably introduced to North America in the late 1800’s as an ornamental. The first records of the species in Washington date back to the 1920’s, when the species was collected near Spokane (1926) and Bingen (1927) (Alex 1962). Growth and DevelopmentGrowth and Development: Dalmatian toadflax is a short-lived perennial. Seedlings generally germinate in the spring. After germination, a primary stem emerges, which may be joined by one to three adventitious stems that develop from the hypocotyl of the seedling; both types of stems can produce flowers. Prostrate vegetative stems also develop adventitiously from the crown and roots of the seedling. The prostrate stems persist over winter and then die when the floral stems begin to develop. Plants produce one to 25 floral stems in the spring, flowering in May. The average life span of a Dalmatian toadflax plant is three years, during which time the plant may produce half a million seeds (Robocker 1974). ReproductionReproduction: Dalmatian toadflax is a perennial species that spreads by horizontal or creeping rootstocks and by seed. A mature plant can produce up to 500,00 seeds, which are primarily dispersed by wind. The seeds may live up to ten years in the soil (Robocker 1974; Morishita 1991). Most seedlings emerge in the spring when soil temperature reaches 8° C at 2.5 cm. Germination in the fall is probably limited by soil water content, as well as possibly seed dormancy (Robocker 1974). Response to Cultural MethodsResponse to Cultural Methods: Intensive clean cultivation can effectively control Dalmatian toadflax. A successful approach includes at least a two year effort, with eight to ten cultivations in the first year and four to five cultivations in the second year (Morishita 1991; Butler and Burrill 1994). Cultivation should begin in early June and be repeated so that there are never more than seven to ten days with green growth visible (Butler and Burrill 1994). Since Dalmatian toadflax seedlings do not compete well for soil moisture against established winter annuals and perennials, control efforts should include attempting to establish and manage desirable species that will compete with toadflax (Morishita 1991; Butler and Burrill 1994). Response to HerbicidesResponse to Herbicides: Picloram, picloram + 2,4-D, and dicamba all provide effective control, although repeated applications of dicamba may be necessary to achieve complete control (Ferrell and Whitson 1988; William et al. 1996). Bio-Control PotentialsBio-Control Potentials: Calophasia lunula, a defoliating moth, is well-established in Washington and reportedly provides good control (William et al. 1996). Rationale for listing: Mature Dalmatian toadflax plants are strongly competitive, especially with shallow-rooted perennials and winter annuals. Because of its competitive ability, Dalmatian toadflax causes negative impacts in pasture, rangelands, and natural areas, where it may outcompete natives or other desirable species. Dalmatian toadflax is still of limited distribution in many parts of Washington. By listing Dalmatian toadflax as a Class B noxious weed, it becomes possible to require control in designated areas, thus preventing its continued spread and decreasing its economic and environmental impacts. References: *Alex, J.F. 1962. The taxonomy, history, and distribution of Linaria dalmatica. Canadian Journal of Botany 40: 295-307. *Butler, M.D. and L.C. Burrill. 1994. Yellow toadflax and Dalmatian toadflax. Pacific Northwest Extension Bulletin 135. Oregon State University, Corvallis, OR. *Dennis, L.J. 1980. Gilkey’s Weeds of the Pacific Northwest. Oregon State University Press, Corvallis. *Ferrell, M.A. and T.D. Whitson. 1987. Evaluation of herbicide treatments for Dalmatian toadflax (Linaria genistifolia ssp. dalmatica (L.) Maire & Petitmengin) control. Research Progress Report, Western Society of Weed Science, Boise, ID. *Ferrell, M.A. and T.D. Whitson. 1988. Herbicide evaluation on Dalmatian toadflax. Research Progress Report, Western Society of Weed Science. *Gaines, X. M. and D.G. Swan. 1972. Weeds of Eastern Washington and Adjacent Areas. Camp Na-Bor-Lee Association, Davenport, WA. *Harris, P. and A.C. Carder. ... Linaria vulgaris Mill., yellow toadflax, and L. dalmatica (L.) Mill., broad-leaved toadflax (Scrophulariaceae) Biological Control Programmes against Insects and Weeds in Canada (1959 -1968), Tech. Communication No. 4. Commonwealth Agricultural Bureaux, Farnham Royal Slough, England. *Hawkes, R.B., T.D. Whitson, and L.J. Dennis. 1985. A Guide to Selected Weeds of Oregon.Oregon Department of Agriculture, Salem. *Hitchcock, C.L. and A. Cronquist. 1973. Flora of the Pacific Northwest. University of Washington Press, Seattle. *Morishita, D.W. 1991. Dalmatian toadflax, yellow toadflax, black henbane, and tansymustard: Importance, distribution, and control. In James, L.F., J.O. Evans, M.H. Ralphs, R.D. Child, eds. Noxious Range Weeds, pp. 399-407. Westview Press, Boulder, CO. *Rizza, A. and P. Pecora. 1980. Biology and host specificity of Chrysomela rossia, a candidate for the biological control of Dalmatian toadflax, Linaria dalmatica. Annals of the Entormological Society of America 73: 95-99. *Rizza, A. and P. Pecora. 1984. Chrysolina gypsophilae (Coleoptera: Chrysomelidae), a potential biocontrol agent of Dalmatian toadflax, Linaria dalmatica (Scrophulariaceae). Annals of the Entomological Society of America 77: 182-187. *Robocker, W.C. 1974. Life history, ecology, and control of Dalmatian toadflax. Technical Bulletin 79. Washington Agricultural Experiment Station, Pullman, WA. *Tucker, G.C. 1987. Additions to the flora of Connecticut. Rhodora 89: 217-219. *USDA-ARS. 1971. Common Weeds of the United States. Dover Publishing, Inc., New York. *William, R.D., D. Ball, T.L. Miller, R. Parker, K. Al-Khatib, R.H. Callihan, C. Eberlein, and D.W. Morishita. 1996. Pacific Northwest Weed Control Handbook. Washington State University, Pullman, WA.
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