Dalmatian Toadflax Spp.
Linaria dalmatica / Linaria genistifolia
Class A Noxious Weed
This plant is new to the state and has been designated a Class A Noxious Weed by the New Mexico Department of Agriculture.
Agricultural Threat
This plant threatens our state's food security and economy by reducing agriculture yields and/or degrading soil resources.
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Livestock Hazard
This plant presents a threat to the health and/or quality of livestock.
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Commercially Available
Despite being classified as a noxious weed, this plant is still widely sold in stores! Keep an eye out, and remember that it is illegal to plant and transport noxious weeds in the state of New Mexico.
QUICK FACTS
- Dalmatian toadflax originates from the Mediterranean. It was introduced to North America in 1874 as an ornamental plant and now thrives in the U.S. and Canada, particularly in semiarid climates and disturbed areas.
- It reproduces prolifically via seeds and creeping root buds, displacing native plants, reducing forage diversity, and harming rangelands and crops. Once established, its extensive root system makes it difficult to eradicate.
- Prevention through strong native ground cover and re-vegetation is key. Manual removal, targeted grazing, and combined strategies are effective, but eradication requires persistence over several years.
1. Overview
A sneaky, slow-growing nuisance.
This tenacious invader, with its bright yellow flowers and silvery-green leaves, may look like it wandered off the set of a children’s fairy tale, but don’t let its charm fool you. Brought to the United States in the late 19th century as an easy-to-grow ornamental, it quickly escaped to become the agricultural nightmare we know today. Unfortunately, this weed is still sold on the market today, as many are fooled by its unique and numerous flowers, which last all summer.
History of Dalmatian toadflax
Dalmatian toadflax hails from the Mediterranean region, where it has adapted to frequent agricultural disturbances. It gets its name from the Dalmatian district it calls home, which contains the countries of Croatia, Bosnia, Hercegovina, and Yugoslavia. It has been propagated as an ornamental throughout Europe since the 1600s. In about 1874, the plant appeared in North America as the plant was sought after for European-style flower gardens. Its bright yellow pigment (along with that of the similar yellow toadflax) was valued for fabric dyes and contributed to its spread. [1,5]
Today, it is widespread across the United States and Canada and continues to be sold as an ornamental for “low-water use landscapes.” The largest infestations exist in Colorado, Utah, Nevada, Wyoming, Montana, Idaho, Oregon, and California. [1,2]
2. ID Guide
What does it look like?
Toadflaxes are perennial, creeping, woody plants with very similar attributes. In the United States, three toadflax species are listed as noxious: Dalmatian toadflax is divided into broadleaf (L. dalmatica) and narrowleaf (L. genistifolia) varieties. There is also yellow toadflax (Linaria vulgaris), which is similar to the Dalmatian toadflaxes but can be distinguished by smaller, whiter flowers and globe-shaped fruit. Yellow toadflax is also a bit shorter (1.5-3 feet), while Dalmatian toadflax is usually taller (3+ feet). Dalmatian toadflax tends to have thick, heart-shaped, waxy leaves, while yellow toadflax leaves are linear and soft. It is possible for Dalmatian toadflax to hybridize with yellow toadflax. Dalmatian toadflax mainly propagates via seed germination with success rates of about 75%, while yellow toadflax primarily spreads by creeping roots, with only a 10% seed germination rate. [1,2,3]
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Key Features
- Plant: Dalmatian toadflax grows up to 5 feet tall with a rough, woody base and mostly dies back in winter (with the exception of prostrate stems) while the roots remain alive underground. New stems emerge from both seed and shoots in April through May. The plant’s form is narrow and upright, with multiple stems growing from a single base (up to 25 stems in its first year). [1,3]
- Roots: There are extensive roots. The vertical roots are rough and large, somewhat branching, and extend down 6 feet or more. The lateral roots branch off from the vertical roots and can extend 10 feet or more and remain close to the soil surface. Buds that develop on the lateral roots quickly produce new shoots. [1]
- Leaves: The heart-shaped (cordate) leaves are alternate, with a dense, waxy-rubbery feel, and have a pale blue-green color. Leaf shapes can be broad or lanceolate (L. genistifolia leaves are narrower). Margins are smooth, and leaf bases clasp the upper part of the stem. [1,3]
- Flowers: The flowers are snapdragon-like and bright yellow-tinged with orange. They are 1 to 1.5 inches long with two lips and a long spur. Flowers, buds, and seed pods can be present simultaneously. Flowers start as clusters at the tip of the stem and become more spaced out further down. The plants have a long flowering period, usually from May to late August. [1,3]
- Seeds: Mature plants can produce up to 500,000 seeds, which remain viable in the soil for up to 10 years. The black, sharply angled seeds begin to appear in late June or early July and may continue until early October. Each seed capsule (fruit) contains a highly variable number of seeds, ranging from 10 to 40. [1]
Bonnie Million, Bureau of Land Management, Bugwood.org
The flowers are snapdragon-like and bright yellow-tinged with orange. They are 1 to 1.5 inches long, with two lips and a long spur.
thurmanjohnson, inaturalist.org
New stems emerge from both seeds and shoots in April through May.
Keath Flint, inaturalist.org
The plant mostly dies back in winter (with the exception of prostrate stems) while the roots remain alive underground.
K. George Beck and James Sebastian, Colorado State University, Bugwood.org
The heart-shaped leaves are alternate, with a dense, waxy-rubbery feel, and have a pale blue-green color.
Young, inaturalist.org
Dalmatian toadflax grows up to 5 feet tall with a rough, woody base. The plant’s form is narrow and upright, with multiple stems growing from a single base (up to 25 stems in its first year).
D. Walters and C. Southwick, USDA, Bugwood.org
Mature plants can produce up to 500,000 seeds, which remain viable in the soil for up to 10 years. The black, sharply angled seeds begin to appear in late June or early July.
3. Infestation Basics
“Dalmatian toadflax has no value as a forage crop. Its danger lies in its ability to crowd out valuable forage, thus reducing range carrying capacity.”
-Rex Warren, 1962
Where does it grow, and how does it spread?
Dalmatian toadflax spreads primarily through its seeds. The plant is weak in its early stages, and eradication requires action during the first weeks of its life.
Due to its high genetic variability, Dalmatian toadflax thrives in various environments, including roadsides, pastures, residential areas, cemeteries, gravel pits, well-drained riparian areas, and waste areas. While it flourishes in disturbed areas, it can also establish itself in undisturbed habitats. This plant often colonizes naturally occurring open spaces within sagebrush ecosystems, ponderosa pine forests, and other woodland or parkland areas. Dalmatian toadflax prefers cool, semiarid climates and is commonly found in sunny locations with well-drained, coarse-textured soils with a neutral pH. It typically grows at elevations ranging from 5,000 to 6,000 feet. [1,6]
Though not long-lived, Dalmatian toadflax grows slowly, investing early energy into its roots. By early autumn of its first year, it sends out lateral stems from the rosette, storing nutrients for overwintering. In the spring of its second year, upright floral stems emerge. These can produce flowers from June through October, but only if the plant has experienced dormancy [1].
Within four weeks, the roots become more established, allowing the plant to aggressively compete with nearby vegetation. Vertical roots can reach 20 inches deep by nine weeks after germination, and adult plants may send roots as deep as 10 feet. Vegetative buds can form as deep as six feet, with most found 2–8 inches below ground on lateral roots, which may extend up to ten feet outward [1,3,4].
Seed production begins on the lower stems while the upper portions may still be flowering. Dispersal starts in early July and can continue into winter, though dry seed capsules can linger on plants for up to two years. With dormancy lasting over a decade and a germination rate around 75%, seeds mostly fall within 18 inches of the parent plant unless water carries them farther [1,3].
Key takeaway: The best preventative measure is to recognize and eliminate the plant within the first few weeks of its spread. Competition from well-established ground cover will strongly discourage the invasion of Dalmatian toadflax.
Why is it so invasive?
Once established, Dalmatian toadflax easily outcompetes native plants and crops by aggressively sequestering available water. In large quantities, the plant can be poisonous to cattle.
Dalmatian toadflax contains quinazoline alkaloids, which are potentially toxic to livestock if ingested in large quantities. While there have been few reported cases of livestock poisoning, it’s worth noting that goats and sheep have been observed consuming these plants with little to no negative impact. [1]
Wildlife, including big game, can be negatively impacted by the loss of diverse forage due to Dalmatian toadflax’s presence. The displacement of native plants primarily affects the economic value of wildlife habitats and rangelands. While individual plants typically live 3–5 years, they rapidly establish new generations. In favorable conditions, stands may persist for over 13 years. Infestations may seem to vanish for years, leading to mistaken conclusions of eradication, only to resurge later from dormant seeds or root buds. [1]
The plant is mildly allelopathic, particularly in low-nitrogen conditions, and it mainly affects grass species. This, in combination with a tendency to carry crop pathogens, makes Dalmatian toadflax a significant threat to crop fields and rangelands. [6]
Key takeaway: The presence of Dalmatian toadflax displaces native plants, reduces wildlife forage diversity, and harms the economic value of rangelands and agricultural fields..
Common risk factors for invasion
- Overgrazing: When livestock are allowed to graze in a single area for too long, they will rip through the existing vegetation and expose the top layer of soil. This creates an opening for Dalmatian toadflax, but this risk can be mitigated by practices that move cattle around more frequently.
- Areas of neglect: Dalmation toadflax needs time to establish and thus can target abandoned areas where it will not likely be disturbed. Events of no-till farming can enable the plant to take hold as frequent disturbance will often damage the root structure. Practices such as overgrazing, lack of crop rotation, and inadequate weed control increase vulnerability to invasion.
- Open spaces: Open sites with long days of full sunlight and little to no canopy, such as pastures, fields, open grazing allotments, south-facing slopes, etc., are at risk for particularly aggressive infestations.
Impacts
Economic
This weed will establish itself as a monoculture through aggressive seed production and vegetative growth. Aside from big game, it can reduce available forage for domestic livestock and, in rare cases, cause harm to cattle. The growth rate of grasses may be up to 2.5 times lower in areas densely infested with Dalmatian toadflax. Occasionally, the weed has been known to affect production in alfalfa fields and pine plantations. Dalmatian toadflax primarily affects wild rangelands and habitats, while yellow toadflax tends to be a greater threat to agricultural lands.[1,6,7]
Ecosystem Health
Dalmatian toadflax displaces native plants once established, leading to a significant loss of floral and faunal biodiversity. This can significantly impact game forage availability, particularly in winter months, and even alter migratory habits. While deer, sheep, some birds, and rodents may use Dalmatian toadflax as a food source, it is generally not considered good forage as most animals tend to avoid it. Some animals may use the plant for shelter, but this is usually in areas where more desirable shelter has been replaced by the very same. [1]
Native grass species seem to be most negatively affected by Dalmatian toadflax. When high groundcover-producing sod grass and bunchgrass are displaced, there is usually an increase in erosion, surface runoff, and sediment deposition. In areas of extreme loss of vegetation, Dalmatian toadflax can somewhat help stabilize the soil. While the weed is known to displace established native plant communities, there have been no reported instances of serious effects on biodiversity in large areas or for specific individual endangered species. [1,6]
Erosion
Dalmatian toadflax significantly increases the risk of soil erosion by outcompeting and displacing native bunchgrasses and groundcover. These native plants play a crucial role in stabilizing soil with their extensive root systems, which help bind the soil and reduce runoff. When yellow toadflax takes over, it replaces these stabilizing plants with its shallow, less effective root structure, leaving the soil more vulnerable to wind and water erosion. In areas where there is already little to vegetation, or in areas of primary succession such as mines, it is possible that toadflax species may help stabilize the soil until more favorable plant communities take over. [1]
4. Management Strategies
Dalmatian toadflax has difficulty settling in areas with well-established grass and forb communities. Promoting native plant development and healthy cover crops is the best first step to preventing the weed from gaining a foothold. Once Dalmatian toadflax has become a fully established monoculture, many management strategies used in conjunction may be necessary to fully eradicate the plant. [1]
One of the most successful management strategies is the successful re-vegetation of desirable plants. Competition from these plants will quickly crowd out potential invasions. While grazing typically increases the risk of infestation, targeted sheep and goat grazing may be beneficial for small patches or hard-to-reach areas. Mowing, grazing, and burning are generally considered ineffective methods due to their inability to target the weed’s extensive root system. Manual removal can be successful in small areas if repeated for 5-6 years. [1,7]
DO’s
- Identify the plant when it is young; young shoots are weak and die easily
- Be wary that this plant is currently on the market and could pop up anywhere!
- Out-compete the plant with well-established crops and native plant communities
DON’T
- Overgraze or frequently till fields and pastures, as this can allow the weed to gain a foothold.
- Mow, burn, or graze as these methods leave behind root fragments, further spreading the infestation.
- Let the plant become established; management becomes more difficult with time, especially after its first year.
** The following information is provided courtesy of the UC Weed Research and Information Center. The Taos Soil and Water Conservation District does not endorse the use of any particular product, brand, or application thereof. **
While grazing usually increases infestation risk, targeted grazing by sheep and goats can be beneficial in specific areas. Methods like mowing, grazing, and burning are generally ineffective due to the weed’s deep root system. However, manual removal can be successful in small areas if repeated over 5-6 years.
Hand-pulling |
Hand pulling is only effective on seedlings before plants become established and the extensive creeping root system develops. |
Mowing |
Mowing can prevent the plant from going to seed, but mowing also stimulates vegetative reproduction from the lateral roots and rhizomes. |
Cultivation |
Tilling on arable lands can be effective but tilling needs to be done every 7 to 10 days over the course of the season and repeated yearly for several years in order to eradicate resprouting root fragments. |
Grazing |
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Eight insects have been introduced and approved by the USDA-APHIS for release as biocontrol agents for both Dalmatian and yellow toadflax in the United States with varying success. Brachypterolus pulicarius, a shoot and flower feeding beetle, can reduce seed set on attacked plants by 74%. Gymnaetron antirrhini and G. netum, both seed-capsule feeding weevils, have been shown to impact seed production in these species. Calophasia lunula, a moth introduced from Eurasia, has been shown to defoliate up to 20% of a plant. Establishment in California is uncertain for these species. Another agent, the toadflax stem-mining weevil (Mecinus janthiniformis) was misidentified as Mecinus janthinus when first introduced in 1995. European research showed that the Mecinus attacking Dalmatian toadflax was actually M. janthiniformis, and that M.janthinus was attacking yellow toadflax. It has had substantial and dramatic impacts on Dalmatian toadflax populations in many western states and is even becoming established in California. The weevil damages the foliage but also destroys flower production. In Colorado, it has reduced Dalmatian toadflax populations 4 to 5 years following release.
- CHEMICAL
- Growth Regulators
- Lipid Synthesis Inhibitors
- Aromatic Aminoacid Inhibitors
- Branched Chain Aminoacid Inhibitors
“The following specific use information is based on published papers and reports by researchers and land managers. Other trade names may be available, and other compounds are also labeled for this weed. Directions for use may vary between brands; see label before use. Herbicides are listed by mode of action and then alphabetically. The order of herbicide listing is not reflective of the order of efficacy or preference.”
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2,4-D Several names |
Rate: 2 to 4 pt product/acre (0.95 to 1.9 lb a.e./acre). Timing: Postemergence when plants are growing rapidly. Applications in spring provide best control. Remarks: 2,4-D is a selective herbicide for broadleaf species. It was found to provide only fair control of Dalmatian toadflax in a California study. Good coverage is necessary. Efficacy is improved when tank-mixed with picloram, chlorsulfuron, or metsulfuron. |
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Aminocyclopyrachlor + chlorsulfuron Perspective |
Rate: 4 to 6 oz product/acre plus 0.25 to 0.5% v/v surfactant Timing: Postemergence when plants are in the rosette stage or in mid-fall when plants are dormant. Remarks: Perspective provides broad-spectrum control of many broadleaf species. It gave excellent control in a California study and appears to be the best product for Dalmatian toadflax. Although generally safe to grasses, it may suppress or injure certain annual and perennial grass species. Do not treat in the root zone of desirable trees and shrubs. Do not apply more than 11 oz product/acre per year. At this high rate, cool-season grasses will be damaged, including bluebunch wheatgrass. Not yet labeled for grazing lands. Add an adjuvant to the spray solution. This product is not approved for use in California and some counties of Colorado (San Luis Valley). |
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Dicamba Banvel, Clarity |
Rate: 4 qt product/acre (4 lb a.e./acre) and water plus 0.25 to 0.5% v/v surfactant Timing: Early postemergence in spring before toadflax reaches bloom stage. Remarks: Dicamba is a selective herbicide for broadleaf species. In a California study, 2 lb a.e./acre gave partial control of Dalmatian toadflax at the rosette stage, and poor control when applied at the bolting or dormant stage. It has a short soil residual activity. Repeated applications may be necessary for better control. |
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Picloram Tordon 22K
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Rate: 1 to 2 qt product/acre (0.5 to 1 lb a.e./acre) plus 0.25 to 0.5% v/v surfactant Timing: Postemergence when plants are growing rapidly in spring before full bloom, or in late summer to early fall. Remarks: At 8 oz a.e./acre in a California study, picloram gave only partial control (80%) when applied at the dormant stage in mid-fall, and poor control at the rosette and bolting stages (< 60% control). Higher rates may be necessary in some areas. High levels of picloram can give long-term soil activity for broadleaves. Tordon 22K is a federally restricted use pesticide. It is not registered for use in California. |
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Picloram + 2,4-D Tordon 101M
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Rate: 2 qt product/acre plus 0.25 to 0.5% v/v surfactant Timing: Postemergence when plants are growing rapidly in spring before full bloom. Remarks: May require annual treatment for 2 to 3 years. High levels of picloram can give long-term soil activity for broadleaves. It is not registered for use in California. |
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Picloram + chlorsulfuron Tordon 22K + Telar
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Rate: 1 qt product/acre Tordon 22K + 1.25 oz product/acre Telar plus 0.25 to 0.5% v/v surfactant Timing: Postemergence when plants are growing rapidly, from bloom through fall. Fall treatments give best control. Remarks: High levels of picloram can give long-term soil activity for broadleaves. Retreatment may be necessary. Tordon 22K is a federally restricted use pesticide. It is not registered for use in California. |
Lorum
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Lorum
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Glyphosate Roundup, Accord XRT II, and others |
Rate: Broadcast treatment: 1 to 2 qt product (Roundup ProMax)/acre (1.1 to 2.25 lb a.e./acre). Spot treatment: 1.5 to 2% solution v/v Roundup (or other trade name) and water to thoroughly wet all leaves Timing: Postemergence when plants are growing rapidly. Applications in early spring provide best control. Remarks: Glyphosate is a nonselective systemic herbicide that may kill non-target partially-sprayed plants. Repeated applications may be necessary for complete control. |
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Chlorsulfuron Telar |
Rate: 2 to 2.6 oz product/acre (1.5 to 1.95 oz a.i./acre) plus 0.25 to 0.5% v/v surfactant Timing: While most recommendations note that applications should be made postemergence when plants are growing rapidly in the bud to bloom stage, others have found that the best timing is when plants are in the rosette stage or when they are dormant in mid-fall. Remarks: Chlorsulfuron is a selective herbicide effective for controlling mainly broadleaves, but also some grasses. A California study showed best results with a rosette or dormant stage application at the highest rate (1.95 oz a.i./acre). Chlorsulfuron can be tank mixed with picloram or 2,4-D. |
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Imazapic Plateau |
Rate: 12 oz product/acre (3 oz a.e./acre) plus 1 qt/acre methylated seed oil in the spray mix Timing: Postemergence in fall when the top 25% of the plant is necrotic. This typically occurs after a hard frost. Remarks: Imazapic is a selective postemergence herbicide effective for controlling broadleaf weeds and some grasses. In one study, it was not found to be very effective for the control of Dalmatian toadflax at 12 oz product/acre. It is not registered for use in California. |
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Imazapyr Arsenal, Habitat, Stalker, Chopper, Polaris |
Rate: 3 pt product/acre (0.75 lb a.e./acre) plus 0.25 to 0.5% v/v surfactant Timing: Some reports note that the best timing is postemergence when plants are growing rapidly, whereas others show that a dormant application in mid-fall was the best timing. Remarks: Imazapyr is a preemergent and postemergence herbicide effective for controlling broadleaf weeds and grasses. In a California study using 3 pt product/acre, excellent control was.only achieved with a mid-fall application to dormant plants. It has fairly long soil residual activity. |
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Metsulfuron Escort |
Rate: 1.5 to 2 oz product/acre (0.9 to 1.2 oz a.i./acre) plus 0.25 to 0.5% v/v surfactant; efficacy is improved with the addition 2,4-D at a rate of 1 qt product/acre Timing: Early postemergence. Remarks: Metsulfuron is a selective herbicide for broadleaf species. In areas where desirable grasses are growing around toadflax, metsulfuron can be used without non-target damage. In one study, however, metsulfuron at 2 oz product/acre gave poor control regardless of timing from the rosette to the dormant stage. It is not registered for use in California. |
5. References
Citations
[1] Sheley, Roger L., and Janet K. Petroff. Biology and Management of Noxious Rangeland Weeds. Oregon State University Press, 1999.
[2] USFS. Field Guide for Managing Dalmatian and Yellow Toadflaxes in the Southwest. 2014.
[3] Ogden, Jennifer A., and Mark J. Renz. “Dalmatian Toadflax (Linaria Genistifolia Ssp. Dalmatica) New Mexico State University Weed-Factsheet.” Weeds.nmsu.edu, NMSU, 6 Nov. 2005, weeds.nmsu.edu/pdfs/dalmatian_toadflax_factsheet_11-06-05.pdf. Accessed 27 Dec. 2024.
[4] Trilochan S. Bakshi and Robert T. Coupland. 1960. VEGETATIVE PROPAGATION IN LINARIA VULGARIS. Canadian Journal of Botany. 38(2): 243-249. https://doi.org/10.1139/b60-022
[5] Webmaster, David Ratz. “Dalmatian Toadflax – Montana Field Guide.” Fieldguide.mt.gov, fieldguide.mt.gov/speciesDetail.aspx?elcode=PDSCR110F0. Accessed 18 Dec. 2024.
[6] Gassmann, André, and Chris Parker. “Linaria Dalmatica (Dalmatian Toadflax).” CABI Compendium, 7 Jan. 2022, https://doi.org/10.1079/cabicompendium.30827. Accessed 31 Dec. 2024.
[7] Jacobs, Jim, and Sharlene Sing. Ecology and management of Dalmatian toadflax (Linaria dalmatica (L.) Mill.). US Department of Agriculture, Natural Resources Conservation Service, 2006.
[8] Gustafsson, Å. Linnaeus’ Peloria: The history of a monster. Theoret. Appl. Genetics 54, 241–248 (1979). https://doi.org/10.1007/BF00281206
Steve Dewey, Utah State University, Bugwood.org
Bonnie Million, Bureau of Land Management, Bugwood.org
Fun Facts
Toadflaxes, as well as snapdragons and foxgloves, are capable of peloria, which is a mutation that causes a flower to switch from bilateral symmetry to radial symmetry, becoming “monstrous” and resulting in a completely new flower. In 1744, Carl Linnaeus was fascinated by this concept and was able to selectively breed thousands of flowers, repeatedly isolating mutations until some plants were producing only peloric flowers. [8]
raingerr, inaturalist.org
K. George Beck and James Sebastian, Colorado State University, Bugwood.org
Eric Coombs, Oregon Department of Agriculture, Bugwood.org
Quillipede, inaturalist.org
Damien Wallace, inaturalist.org
Matt Berger, inaturalist.org
John D Reynolds,inaturalist.org