United States Department of Agriculture 

NATURAL RESOURCES CONSERVATION SERVICE 

Invasive Species Technical Note No. MT-3 

July 2006 

Ecology and Management of Dalmatian toadflax (Linaria dalmatica (L.) Mill.) 

Jim Jacobs, NRCS Invasive Species Specialist 

 Sharlene Sing, Research Professor, Montana State University, Bozeman 

Abstract 

Dalmatian toadflax is a short-lived perennial herb native to the Mediterranean coastal regions of 

Europe and western Asia. Its name is derived from the Dalmatian Coast of the Adriatic Sea 

located within its native range. This species has escaped cultivation as an ornamental, a source 

of fabric dye, and as a medicinal plant to become an invasive weed. Dalmatian toadflax has been 

reported in all but nine Montana counties, with particularly heavy infestations in Broadwater, 

Jefferson, Lewis and Clark, and Bighorn Counties (see Figure 1). A distribution increase graph 

from the Invaders Database (http://invader.dbs.umt.edu) suggests that Dalmatian toadflax is 

currently in the exponential population growth phase of invasion in Montana, making it a 

considerable threat to resource conservation in this state. Dalmatian toadflax is adapted to a 

wide range of habitats but it is most problematic in dry, open grassland and forest sites, along 

roadsides, and on disturbed sites with coarse, well-draining soils. Grass production can be 2.5 

times lower in dense infestations than similar areas without Dalmatian toadflax. 

Figure 1. Dalmatian toadflax infestation (yellow) reported in Montana in 2001. Each yellow dot on 

the map represents one section reporting Dalmatian toadflax. Permission to use this map was 

granted from Diana Cooksey, Adjunct Instructor, MSU-LRES and Coordinator of Montana 

Agricultural Potential System (MAPS). Additional information about section based maps can be 

found at: http://www.montana.edu/places/mtweeds/databasedev.html. 

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Dalmatian toadflax seedlings are not considered to be effective competitors with established 

plants or seedlings of native grasses. However, once established, populations of Dalmatian 

toadflax are very competitive with both grasses and forbs, and are therefore difficult to eradicate. 

Maintenance of competitive plant communities is essential to preventing the spread of this weed. 

The extensive reproductive root system of Dalmatian toadflax and the ability of its seeds to 

persist for up to ten years in the soil enable it to regenerate after all types of control applications. 

Six insect species have been approved for release in the United States as biological control 

agents for Dalmatian toadflax. The most recently introduced species, Mecinus janthinus, 

commonly known as the toadflax stem-mining weevil, has been observed to reduce toadflax 

populations in Canada, Washington, and Montana. Other insect species attack toadflax roots, 

growing points of the stem, seeds and flowers. 

Sheep and goats will graze Dalmatian toadflax once they are trained to eat it and have been used 

to reduce weed biomass and seed production. Cows and livestock have also been observed to 

browse on Dalmatian toadflax. Herbicidal control requires high application rates and repeated 

applications. Picloram (1 qt./acre), metsulfuron (1.5 oz./acre), clorsulfuron (1.5 oz./acre), and 

imazapic (12 oz./acre applied in the fall) applied at bloom in May or June or to fall re-growth 

have resulted in short-term reduction of Dalmatian toadflax populations. The longevity of 

control will depend on site conditions, the intensity of competition from other plant species, and 

grazing management. Cultural controls (tilling, mowing, and burning) when applied alone are 

generally ineffective in controlling Dalmatian toadflax, but may improve the effectiveness of 

herbicidal, biological, and grazing control when used in an integrated management program. 

Biology and Identification 

Two species of Dalmatian toadflax are considered noxious in the United States: broad-leaved 

Dalmatian toadflax (L. dalmatica) and narrow-leaved Dalmatian toadflax (Linaria genistifolia). 

Both are in the Scrophulariaceae (figwort) taxonomic family. Only the broad-leaved species is 

known to be invasive in Montana. Both Dalmatian toadflax species and yellow toadflax (Linaria 

vulgaris) have hybridized in the laboratory so incidents of natural hybridization should be 

expected. 

Seeds. Dalmatian toadflax is a perennial that can produce copious amounts of seeds. A single 

plant growing under ideal conditions can produce several hundred thousand long-lived seeds. 

Environmental conditions and plant competition can have a major influence on the number of 

seeds produced. Dalmatian toadflax populations were observed to produce an average of seven 

seeds per plant where there was a competitive plant community, compared to 79 seeds per plant 

where competitive plants were sparse in Jefferson County, Montana. Prescribed fire increased 

seed production to 355 and 158 per plant, respectively, at the low-competition versus highcompetition site. Prescribed fire increased Dalmatian toadflax seed production from an average 

of 29 to 1,328 seeds per plant on one study site. Studies have shown that seeds can maintain 

viability when in the soil for ten years or more. 

Seedlings. Some seeds germinate in the fall, but most germinate in the spring, as early as March 

on south-facing slopes. Emerging shoots are thin and delicate with fine linear leaves. Dalmatian 

toadflax seedlings are not strong competitors due to their low tolerance of droughty conditions 

NRCS−Montana−Technical Note−Invasive Species−MT-3 2
compared to co-occurring species. In greenhouse competition studies, seedlings of bluebunch 

wheatgrass (Pseudoroegneria spicata) were over two times more competitive than Dalmatian 

toadflax seedlings when the two species were planted at the same time. Seedling root 

development is initially slow; however, in nine weeks seedlings roots are capable of growing up 

to 20 inches deep and producing vegetative buds that can give rise to new shoots. 

Roots. Dalmatian toadflax can produce deep taproots and thick creeping rhizomes that are 

nearly white in color. Underground adventitious buds on the root and root crown of a wellestablished plant can generate reproductively viable ‘daughter’ stems. Vegetative regeneration 

from buds on root crowns and lateral roots partly explains the competitiveness of Dalmatian 

toadflax. Energy stored in the roots allows shoots to grow regardless of competition from a 

healthy plant community. Root energy reserves are greatest in the fall and lowest pre-bloom in 

June. 

Figure 2. The roots of Dalmatian toadflax showing the top part of the thick taproot and lateral 

rhizomes running left and right. 

Vegetative Stems. Shoots from root or crown buds begin emerging early in the spring. 

However, emergence continues through June so that relatively sparse stands in the spring may 

become denser in the summer. Leaves are alternate along the stem, heart-shaped and broadest at 

the leaf base, and clasping the stem. Both stems and leaves are hairless and have a thick waxy 

coating that gives their surface a whitish to bluish appearance. Short, prostrate stems with tightly 

clustered linear leaves giving the plant a rosette-like appearance grow from root buds in the fall. 

These rosette-like plants may remain green through the winter and develop flowering shoots in 

the following summer. 

NRCS−Montana−Technical Note−Invasive Species−MT-3 3
Figure 3. A Dalmatian toadflax stem showing the heart-shaped, hairless, clasping leaves and the 

waxy surface. 

Flowers. Under field conditions, Dalmatian toadflax apparently requires both a winter 

dormancy period and exposure to temperatures between 50° and 68° F (10° to 20° C) to initiate 

flowering, which may explain its northerly geographic distribution. Because it is a short-lived 

perennial with individual plants living an average of three to five years, seed production is 

important to stand survival. Flowering begins in June and can continue through September and 

into November under ideal conditions. The flowers are bright yellow with an orange center, are 

shaped similar to the blossoms on snapdragon, have a distinct spur at the base, and are relatively 

widely spaced on spike-like racemes (see Figure 4). The racemes form at the growing tip of the 

primary stem and secondary flowering stems can grow from buds in the leaf axils which gives 

the plant a branched appearance. Flowering is indeterminate; blooming occurs from the base of 

the stem toward the elongating stem tip and new flowers are produced as long as conditions are 

favorable. Stems can grow to over three feet (one meter) tall. Starting in July, flowers develop 

into cylindrical capsules that may contain 40 or more seeds. Stems die when soil moisture is 

depleted or in freezing temperatures. However, once dead, the stout stems can remain upright 

and disperse seeds throughout the winter. 

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Figure 4. Dalmatian toadflax flowers showing the snapdragon-like shape, prominent spur at the 

base of the flower, and branching at the leaf axils. 

Spread. In cases other than intentional horticultural plantings, spread of Dalmatian toadflax 

occurs predominantly through seed dispersal. Most seeds fall within five feet (1.5 m) of the 

parent plant. Dalmatian toadflax seeds are small (about the size of an alfalfa seed) with a papery 

wing that may facilitate wind dispersal. Long-distance wind dispersal has been suggested during 

the winter when seeds fall from upright stems onto crusted snow. Birds, other wildlife, and 

domestic animals that consume the seed capsules may disperse seeds long distances when 

undigested, viable seeds pass through their digestive tracts. Population expansion is achieved 

through short-distance seed dispersal and by vegetative propagation from creeping roots. On 

cultivated land, root fragments clinging to farm implements can initiate new infestations. 

Habitat. Dalmatian toadflax is adapted to a wide variety of habitats from open grasslands and 

savannas, to open forest sites. Infestations are commonly found on well-drained, coarse-soils, 

and on steep slopes that are prone to erosion disturbance. The natural disturbance on these sites 

provides opportunities for competition-free establishment compared to heavier soils and level 

sites with competitive plant communities. Grazed lands not given sufficient rest between grazing 

events are susceptible to Dalmatian toadflax invasion. A site disturbed by mining, road 

construction or where the competitiveness of the plant community is compromised is also 

susceptible to invasion. 

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Management Alternatives 

Herbicide1/ 

The thick waxy leaf cuticle, long-lived seeds, and robust, creeping, reproductive root system are 

biological characteristics of Dalmatian toadflax that present a challenge for effective herbicidal 

management. Results of herbicide trials on Dalmatian toadflax have been variable with very 

good control in some applications to nearly no control in other applications of the same 

treatment. Site conditions including soil characteristics and the presence of competitive plants, 

and the chemistry, rate, and timing of application will affect the results of herbicide management 

of Dalmatian toadflax. 

Herbicide applications on fall re-growth or in the spring up to early bloom have been most 

successful in controlling Dalmatian toadflax. The waxy leaf surface may be less developed at 

these times compared to summer allowing more herbicide to enter the plant. Plants are also 

actively growing at these times which facilitates the movement of herbicide to target sites. 

Herbicide application at pre-bloom may have the greatest long-term Dalmatian toadflax 

suppression because root reserves are at their lowest level at that time. 

Herbicides effective for controlling Dalmatian toadflax are listed in Table 1. In addition, 

chorsulfuron (Telar®) is also effective; however it is not currently labeled for Dalmatian toadflax 

control. Herbicide trials have shown that Dalmatian toadflax can be controlled for up to three 

years with chlorsulfuron or metsulfuron (1.5 oz./acre with a non-ionic surfactant) applied in the 

fall or spring, or with picloram (1 qt./acre) applied in the spring up to early bloom. Imazapic 

(12 oz./acre with 1 qt. methylated seed oil-MSO) is most effective when applied to late fall regrowth. 

 

Table 1. Chemical and product name, recommended application rate, soil residual half life, and 

ecotoxicity of herbicides commonly used to control Dalmatian toadflax. 

Chemical Name Product Name Rate/Acre Half Life-Days Ecotoxicity (LC50/EC50) 

Imazapic Plateau 12 oz. 31-233 >100 mg/L 

Metsulfuron Escort/ 

Cimarron 

1.5 oz. 14-180 >150 mg/L 

Picloram Tordon 1-2 qt. 90 10-100 mg/L 

Grazing 

Dalmatian toadflax vegetation contains alkaloids thought to be mildly toxic to grazing animals. 

In the western states, no toxic effects have been observed in animals that utilize this weed. 

Cattle, sheep, and goats have been observed to eat Dalmatian toadflax, but it is often not their 

preferred forage, and timing of palatability is still under study. Cattle have been observed to eat 

the pre-bloom stems in the spring, sheep will utilize the weed throughout the summer, and goats 

have eaten Dalmatian toadflax in the spring and fall. Sheep and goat grazing may be a good 

option for management of infestations that are difficult to access. 

1/

Any mention of products in this publication does not constitute a recommendation by the NRCS. It is a 

violation of Federal law to use herbicides in a manner inconsistent with their labeling. 

NRCS−Montana−Technical Note−Invasive Species−MT-3 6
Recent studies show that sheep and goats can be used to manage Dalmatian toadflax. Sheep 

trained to eat Dalmatian toadflax consumed nearly 90 percent of the weed vegetation with little 

effect on grass or other forb species. Sheep grazing initially increased Dalmatian toadflax 

density, most likely due to increased root-sprouting, but in the long-term it is expected that 

densities of Dalmatian toadflax will decrease under sheep grazing management. Sheep and goats 

will consume flowers and thereby reduce seed production. Grazing with sheep or goats after 

herbicide application may be used to reduce Dalmatian toadflax regeneration, potentially 

increasing the time between herbicide re-applications. Toadflax seed capsules appear to be a 

preferred food for many grazing animals. However, to prevent spread of Dalmatian toadflax 

seeds through their feces, grazing animals that may have consumed these seeds should be 

contained and fed weed-seed free forage for five days before being moved to weed-free areas. 

Biological 

Six biological control insects have been released in the United States to control Dalmatian 

toadflax (see Table 2). Two insects released to manage yellow toadflax (Linaria vulgaris) also 

attack Dalmatian toadflax, and there are four insects currently being considered for hostspecificity testing in Europe. 

The flower beetle, Brachypterolus pulicarius, and the seed capsule weevil, Rhynusa (formerly 

Gymnetron) antirrhini, have established throughout western North America but have not proven 

to be effective in controlling Dalmatian toadflax. The toadflax moth, Calophasia lunula, is also 

well established and distributed throughout in the western region. The larvae (caterpillars) 

defoliate all stages of Dalmatian toadflax but only apparently influence the vigor or density of 

seedlings. The toadflax root-boring moth, Eteobalea intermediella, and the toadflax root-galling 

weevil, Gymnetron linariae, were first released in Montana in 1996 but efforts to verify their 

establishment and assess their impact on target weed populations have been significantly 

impeded by their cryptic lifestyle. 

The toadflax stem-mining weevil, Mecinus janthinus, has shown promise for controlling 

Dalmatian toadflax in areas of southern British Columbia and Northern Washington where 

reductions in density and vigor have been reported. The adults of this weevil feed on the leaves 

and deposit eggs in the stems beginning in May. The larvae develop and feed in the stem where 

they mine the central part of the stem and disrupt water movement to leaves and flowers. Larvae 

generally require a stem of >9 mm to successfully develop into adults. Pupation occurs within 

the stem in early August; fully developed adults remain within the natal stem where they overwinter. Canadian researchers report that over-wintering survival of M. janthinus has been 

greatest at sites that maintain significant snow cover over the course of the winter. This weevil 

prefers hot, dry, forested areas or grasslands with greater than 30 percent total vegetation cover 

as protection against extreme summer heat. 

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Table 2. Biological control insects for management of Dalmatian toadflax, the site of attack on the 

plant, insect life stage and plant life stage for collection, and the collection method for redistribution. 

Insect Type Site of Attack Collection Collection Method 

Brachypterolus pulicarius beetle flower adult sweep net/tray 

Calophasia lunula moth foliage larval tray 

Eteobalia intermediella moth roots pupal/adult n/a 

Rhinusa antirrhini weevil seeds adult sweep net/tray 

Rhinusa linariae weevil root adult n/a 

Mecinus janthinus weevil stem adults tray 

Cultural 

Cultural control methods applied by themselves including tilling, mowing, burning, hand pulling 

and grubbing are not effective for reducing Dalmatian toadflax populations due to regeneration 

from the extensive reproductive root system. Irrigation and fertilization to increase the 

competitiveness of grasses should only be applied after herbicide suppression. Mowing has little 

effect on root reserves but may reduce flower and seed production if repeated often. Carefullytimed cultural methods may improve the effectiveness of other control practices. 

Burning. Prescribed burning will not control Dalmatian toadflax. The soil below a prescribed 

burn does not reach temperatures hot enough to kill roots or rhizomes. Prescribed burns can 

double Dalmatian toadflax biomass and increased seed production ten-fold. If prescribed 

burning is used as a management practice in Dalmatian toadflax infestations, herbicidal control 

or sheep or goat grazing should also be used to prevent increasing Dalmatian toadflax. 

 

Tilling. Tilling is not practical for managing Dalmatian toadflax. It requires cultivation 

beginning in early June and must be repeated every seven to ten days. This disturbance is more 

likely to spread root fragments that can develop into new infestations than reduce infestations. 

Disturbance also favors establishment of the weed from seed. Tilling should only be used in 

combination with herbicidal management and re-vegetation. 

Re-vegetation. Competitive plants are important in preventing infestations of Dalmatian 

toadflax. However, there is little information on re-vegetation of infestations with grasses or 

other species. Research in Wyoming showed Bozoisky Russian wildrye, Hycrest crested 

wheatgrass, and Luna pubescent wheatgrass were competitive with Dalmatian toadflax and 

limited its re-establishment. On healthy grassland sites, herbicidal suppression of Dalmatian 

toadflax has successfully restored perennial grasses. Often Dalmatian toadflax invades steep 

sites with coarse soils and low productivity. On these sites it is difficult to justify the expense of 

re-vegetation based on economic return. Aerial seeding of native grasses on sites burned by 

wildfire has been successful in preventing the spread of Dalmatian toadflax. 

Refer to Montana Plant Materials Technical Note 46, ‘Seeding Rates and Recommended 

Cultivars,’ and Extension Bulletin EB19 ‘Dryland Pasture Species for Montana and Wyoming’ 

for seeding rate guidance and re-vegetation species selection. State and area resource specialists 

can help determine the most appropriate, site-specific species mix, timing of seeding, and 

seeding methods. 

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Integrated Pest Management 

Plant community composition and Dalmatian toadflax density are important considerations in 

planning IPM for Dalmatian toadflax infestations. Research has shown that in rangeland plant 

communities with high canopy cover of a diversity of forb species, and low density of Dalmatian 

toadflax, herbicidal control decreased forb cover with little or no significant reduction in 

Dalmatian toadflax density. This result suggests that there may be a threshold of Dalmatian 

toadflax density below which herbicidal control does more harm to the plant community than 

good as measured by toadflax control. Based on these results, herbicide application over a largescale infestation of Dalmatian toadflax with an average density of ten flowering stems/m2

 or less 

is most likely not justified. On these sites grazing with sheep or goats along with prescribed 

cattle grazing management, or as an alternative, release of Mecinus janthinus, should be used to 

prevent an increase in Dalmatian toadflax and potentially reduce density over the long-term. 

Infestations with greater than 25 flowering stems/m2

 and a healthy grass stand should be sprayed 

to reduce Dalmatian toadflax density below ten stems/m2

. Biological control or prescribed 

grazing should then be used to maintain Dalmatian toadflax at low levels. On harsh sites with 

low productivity, prescribed grazing or biological control should be used to reduce Dalmatian 

toadflax. Grazing and Mecinus janthinus are not compatible because the grazing animals 

consume the Dalmatian toadflax stems where the insects live and over-winter. Currently, 

Mecinus janthinus is the most promising biological control agent for managing Dalmatian 

toadflax. 

An integrated Dalmatian toadflax weed management program will include prevention, early 

detection and small-scale eradication, containment, and large-scale population reduction. 

Prevention is guided by how Dalmatian toadflax spreads and its requirements for establishment 

and includes maintaining competitive plant communities and preventing seed imports by using 

weed-free feed and seed, cleaning equipment before application on weed-free areas, and 

containing grazing animals that have fed in Dalmatian toadflax infestations for five days before 

moving them to weed free areas. Early detection and small-scale eradication is achieved through 

persistent survey and herbicide application. Dalmatian toadflax populations are contained by 

herbicidal control of population boarders and satellite populations, control actions that reduced 

seed production such as sheep or goat grazing and biological control insect releases, and 

cultivation of competitive plants. Large-scale population reduction is achieved over the longterm by applying management alternatives such as prescribed grazing that includes sheep or goat 

grazing, and biological control insects that reduce the Dalmatian toadflax population fitness and 

increase the fitness of desirable, competitive plant populations. 

References 

Coombs, E. M., J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. (eds). Biological control of 

invasive plants in the United States. Oregon State University Press, Corvallis. Pages 

380-395. 

Lajeunesse, S. 1999. Dalmatian toadflax. In: Biology and Management of Noxious Rangeland 

Weeds. Oregon State University Press, Corvallis. Pages 202-216. 

Wilson, L.M., Sing, S.E., Piper, G.L., Hansen, R.W., De Clerck-Floate, R.A., MacKinnon, D.K., 

and Randall, C.B. 2005. Biology and biological control of Dalmatian and yellow toadflax. 

Report FHTET-05-13, USDA Forest Service. 

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