Dalmatian Toadflax

Identification & Biology
Latin Name : Linaria dalmatica
Category : Terrestrial Plants
Description :
  • Creeping-rooted perennial
  • Grows from 0.5 to 1.2 m tall
  • Bright yellow “snapdragon-like” flowers
  • Leaves are waxy, light green and heart-shaped

Dalmatian toadflax reproduces by seed and vegetative propagation. Individual plants live up to five years. Toadflax plants begin emerging in the early spring, with flowering occurring from May-August. A mature plant can produce up to 500,000 seeds annually, and the seeds can remain viable for up to 10 years. Prostrate stems emerge in September; they are tolerant of freezing and are associated with floral stem production the following year. Root buds can form on fragments as short as 1 cm in length and as early as 2-3 weeks after germination. These buds can grow their own root and shoot systems, and become independent plants the next year. Look-a-likes: Yellow toadflax (L. vulgaris) grows only to 0.6 m tall and has leaves that are long, narrow and pointed at both ends. The flowers also have an orange spot on the lower lip.

Habitat

In British Columbia, Dalmatian toadflax occurs most frequently in the Southern Interior invading open, low-elevation, coniferous forests and adjacent shrub-steppe habitat. It is most commonly found on sandy or gravely soil on roadsides, railroads, pastures, cultivated fields, rangelands and clear cuts. While toadflax can rapidly colonize disturbed or cultivated ground, plants can also invade healthy native plant communities.

Impact & Risks

A persistent and aggressive invader, Dalmatian toadflax has expanded significantly in the western United States and western Canada during the last few decades. Toadflax displaces native vegetation, thereby altering the species composition of natural communities. It is a strong competitor, quickly colonizing open sites, and adapting to a wide range of environmental conditions. Once Dalmatian toadflax becomes established, it is particularly competitive with winter annuals and shallow-rooted perennials. Toadflax can reduce forage production for livestock and other ungulates. While it is generally considered unpalatable to livestock, some researchers claim that Dalmatian toadflax is toxic to livestock when consumed in significant amounts. Reports of livestock poisonings are rare.

Prevention & Mitigation

The most effective way to ensure that your lands do not become infested with Dalmatian toadflax is by prevention. Here are some recommendations to prevent invasion on your property:

  • Maintain your land in a healthy, vigorous condition to ensure a productive plant community
  • Regularly patrol your property for Dalmatian toadflax plants and immediately treat new patches.
  • Cooperate with adjacent landowners and encourage them to control Dalmatian toadflax.
  • Immediately re-vegetate disturbed, bare soils with a suitable seed mix that provides dense, early colonization to prevent weed invasion.
  • Clean vehicles and machinery of plant material and soil before leaving a toadflax infestation.
  • Follow a well-designed grazing plan; excessive livestock grazing reduces competition and favours invasive plants.
Treatment & Disposal

Individual plants and small patches of Dalmatian toadflax can be hand-pulled or hand-cut to prevent seed formation. Hand pulling is most successful where soils are sandy and/or moist, allowing for removal of as much root as possible. Hand-cutting toadflax stands to ground level in spring or early summer is an effective way to eliminate seed production and dispersal, but it will not destroy plants. Mechanical mowing might even be less effective on toadflax than cutting because it leaves several centimetres of stem above the soil surface that may allow plants to re-sprout more rapidly. Physical removal must be repeated annually for at least ten years to completely deplete the seed bank. Chemical control is also an option. Before applying herbicides, read the label for full use and precautionary instructions. Consult the most recent edition of the Alberta Agriculture and Forestry Crop Production Guide for the selection and application of chemicals to protect your crop. Biological control agents have been released in BC, the most successful being a black, stem-boring weevil, Mecinus janthiniformis. Adults of this bioagent feed on new shoots and create “shot holes” in the leaves, while larva feed from within the plant, damaging the internal growth tissues. Notable reductions have been observed in populations of Dalmatian toadflax throughout the Okanagan Valley as a direct result of attack by M. janthiniformis. Another agent that also feeds on toadflax leaves is Calophasia lunula, a pale to dark brown moth with white markings. It is most easily distinguished during its larval phase, when it is pearl-coloured with five yellow stripes along the back and sides. Another bioagent, Rhinusa antirrhini, is a weevil that feeds on seed capsules later in the summer.

Okanagan Distribution

Priority Level Definitions

Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.