Dalmatian toadflax [Linaria genistifolia (L.) Miller ssp. dalmatica (L.) Maire & Petitm.][LINDA] [CDFA list: A] Photographs Map of Distribution
Yellow toadflax [Linaria vulgaris Miller][LINVU] Photographs
SYNONYMS:
GENERAL DESCRIPTION:Herbaceous perennials, with creeping roots and showy yellow flowers, to 1.2 m tall. Plants are highly competitive for soil moisture with winter annuals and shallow-rooted perennials. Infestations often form large colonies, displacing desirable vegetation. On infested rangeland, livestock typically avoid grazing plants. Yellow toadflax was reportedly first introduced to North America from Europe, by a man named Ranstead, who accompanied William Penn to present day Pennsylvania in the late 1600s. Yellow toadflax has since widely escaped cultivation. Yellow toadflax has been used medicinally and as a dye and can harbor cucumber mosaic and broad bean wilt viruses. Numerous insects attack the toadflaxes; however, at publication time, none have been approved for use as biocontrol agents in California. Both species are native to the Mediterranean region.
SEEDLINGS:Compete poorly with established vegetation for soil moisture. Seedlings that have lost their cotyledons resemble new shoots from roots. Seedlings initially develop a taproot.
MATURE PLANT:Stems typically branched near the top. Leaves primarily alternate, but crowded and often appearing opposite or whorled, especially near the bases of stems. Leaf margins entire. Aboveground parts die back to the ground in fall.
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ROOTS and UNDERGROUND STRUCTURES:Plants develop an extensive system of vertical and creeping lateral roots that produce new shoots. Root fragments can produce new plants. Roots can associate with vesicular-arbuscular mycorrhizae. Dalmatian toadflax roots can penetrate soil to depths of 2 m or more. Lateral roots are typically 5-20 cm below the soil surface and can extend outwards to 3.5 m in all directions. Acclimated roots of yellow toadflax can survive temperatures as low as –15º C (5º F).
FLOWERS:May-September. Flowers showy, yellow, snapdragon-like. Corolla two-lipped, 5-lobed, with a long, +/- straight, downward pointing spur near the base of the lower corolla tube. Stamens 4, in 2 pairs. Self-incompatible. Insect pollinated.
FRUITS and SEEDS:Capsules +/- round, 2-chambered, opening by irregular slits at the apex to release numerous black to brown seeds.
POSTSENESCENCE CHARACTERISTICS:Stiff stems with attached seed capsules containing seed can remain erect for an extended period during the winter.
HABITAT:Disturbed open sites, fields, pastures, degraded rangelands, roadsides, agronomic and perennial crops. Both species tolerate a broad range of climatic conditions and soil types.
DISTRIBUTION:Both species grow throughout California, except the Great Basin and desert regions. To 1000 m (3300 ft). At publication time Dalmatian toadflax is not known to occur in the following counties: Amador, Fresno, Imperial, Kings, Marin, Mariposa, Orange, Riverside, San Benito, Santa Clara, Santa Cruz, Stanislaus, Sonoma, Sutter, Toulumne, Yuba. Counties with previous infestations now eradicated: Alameda, Contra Costa, Los Angeles, Napa, San Luis Obispo, San Mateo, Santa Barbara, Solano, Tulare, Yolo.
PROPAGATION/PHENOLOGY:Reproduces by seed and vegetatively from creeping lateral roots. Most seed falls near the parent plant. Some seed disperses short distances with wind and to greater distances with water, soil movement, and by clinging to the feet, fur or feathers of animals. Seed production and viability is highly variable, depending on out-crossing and presence of pollinators. Seeds germinate in spring and fall when conditions become favorable. Germination occurs on the soil surface and to a depth of 3 cm. Plants can rapidly colonize a site by vegetative reproduction from creeping roots. Dalmation and yellow toadflax can hybridize.
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Overgrazing, soil disturbance, or removal of established perennial vegetation enhances survival, especially of seedlings. Occasional cultivation can disperse root fragments. Mowing or burning before flowers mature can prevent seed production, but does not prevent spread by creeping roots or affect buried seed. Intensive cultivation for at least 2 years (every 7-10 days the first year and 4-5 cultivations the second year) and planting competitive perennial and annual grasses discourages survival.
SIMILAR SPECIES:Other ornamental toadflaxes that have escaped cultivation in California include purple toadflax [L. purpurea (L.) Miller], Morocco toadflax [L. maroccana Hook f.], clovenlip toadflax [Linaria bipartita Willd.], and pineneedle toadflax [Linaria pinifolia (Poiret) Thell.]. These species are easy to distinguish from Dalmation and yellow toadflax as they all typically have red to purple flowers. Morocco toadflax is often a component of commercial wildflower seed. These species occasionally grow on disturbed sites in the Central-western (CW) and/or Southwestern (SW) regions to 500 m (1700 ft). All are native to the Mediterranean. Refer to the table below for distinguishing characteristics. In addition, oldfield or blue toadflax [Linaria canadensis (L.) Dum-Cours.][LINCA] is a native species that may be confused with escaped ornamental toadflaxes. It is usually not considered a weed in California and is included in the table below for identification purposes only. Oldfield toadflax occurs on sandy sites in the North Coast, North Coast Ranges, Central Valley, Sierra Nevada foothills, Central-western region, Transverse Ranges, and Peninsular Ranges; to 1800 m (5900 ft).
flower color
& length
light purple
15-18 mm
variable, usually purple
20-38 mm
reddish-purple
18-20 mm
purple
southern
CW
purple to blue
10-24 mm
CONTROL METHODS:
Prevention: Dalmation toadflax is an invasive perennial from Southern Europe. It was brought to California as an ornamental in the late 1800's due to its showy yellow flowers. It quickly escaped cultivation, and is now found throughout the state. Dalmation toadflax is adapted to a wide range of soil and environmental conditions, but thrives on coarse textured well-drained soils in open areas along roadsides and in rangelands and some cropping systems. Disturbance appears to be closely related to the invasion potential of dalmation toadflax. Initially, seedlings are poor competitors and establishment is difficult where competitive vegetation is present. However, established plants compete very strongly for limiting resources. Dense stands reduce grazing capacity and may displace native plants. Seeds are very small and are adapted for wind dispersal.
Mechanical: Grubbing or hand pulling may be effective for controlling small infestations, but must be repeated several times a year for many years. Dalmation toadflax has an extensive underground network of lateral roots with numerous dormant root buds. Complete removal of the root system is generally infeasible. Mowing generally provides very limited control of dalmation toadflax. Mowing may prevent seed production, but does not appear to significantly deplete root carbohydrate reserves. Mowing also reduces the competitive effects of surrounding vegetation. Mowing should not be used if plants have set seed, as this will facilitate seed dispersal. Intensive cultivation may be utilized on arable land where dalmation toadflax is a problem. Eradication has been accomplished by cultivating every 7-10 days during the growing season for two years. However, this strategy is generally economically and environmentally unacceptable. Cultivation may also bury seed, which may be viable in the soil for over ten years. Tillage equipment should also be thoroughly cleaned after being used in infested areas, as seeds and root segments may be carried to new areas.
Biological: Two insects active on dalmation and yellow toadflax were accidentally introduced into the United States in the early 1900's. The toadflax flower feeding beetle (Brachypterolus pulicarius) and the toadflax capsule weevil (Gymnetron antirrhini) are well established the Northwest. Establishment in California is uncertain. Both significantly reduce yellow toadflax seed production, but their effect on dalmation toadflax is unclear. Registration of a dalmation toadflax specific strain of G. anterrhini is expected in the near future. Although several other insects are currently being tested, the only registered biocontrol agent for dalmation taodflax is the toadflax moth, Calophasia lunula. This moth is highly active in the larval stage and will dramatically defoliate plants, reducing seed production and root carbohydrate levels. The moth is established in Idaho, Montana, and Washington, but is only readily available for redistribution in Washington. Larvae may be collected from plants, stored in cool cardboard containers with ample plants for food, and transferred to new locations for release. Larval feeding activity is in May and June. These moths may not establish in heavily shaded areas or in areas with heavy rainfall.
Chemical: Chemical control of dalmation toadflax has been highly variable. Picloram has been the most effective herbicide for toadflax control, but is not currently labeled in California. Rates range from 0.25 - 1.0 lb ae/A. Picloram efficacy may be reduced where heavy rains move it below the root zone, or where incorporation is limited due to a lack of moisture, and subsequent photodegradation occurs. Picloram will injure or kill most other dicots and some monocot seedlings. Fall applications have been more effective in Colorado and Montana. Optimal timing in California's Mediterranean type climate is uncertain. Dicamba may be effective at very high rates (4 lb ae/A) and 2,4-D alone is generally ineffective. Glyphosate may be applied as a spot treatment to plants in early bloom, but will also kill other vegetation it contacts.
Grazing and Burning: Although deer may occasionally browse dalmation toadflax, livestock will avoid it. It is known to be toxic to livestock, but reported cases are few, due to its unpalatable nature. Cattle numbers should be reduced on range infested areas to prevent overgrazing of the desirable vegetation. Cattle should also be removed from infested areas before seed production. Cattle may also facilitate dispersal as the tiny seeds easily catch in hair or fur, or pass through the digestive system. Good grazing practices combined with weed monitoring on rangeland may be the best preventative measure for invaders such as dalamation toadflax. There is little available information regarding toadflax control with fire. Fire may control seedlings and established plant topgrowth, but new shoots will rapidly emerge from lateral root buds if there is available soil moisture. These new shoots may proliferate in the burned nutrient rich environment, especially in the absence of competition. Additional research is needed in this area.
Integrated management: Dalmation toadflax readily invades disturbed areas where an open biological niche occurs. This was most apparent when it began to invade declining areas of Hypericum perforatum in the 1950's and 1960's. Filling these niches is essential to sustainable weed management. Establishing competitive vegetation such as perennial grasses is critical to prevent reinfestation.