Linaria dalmatica (dalmatian toadflax)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Rainfall Regime
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Impact Summary
- Economic Impact
- Environmental Impact
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Linaria dalmatica (L.) Mill.
Preferred Common Name
- dalmatian toadflax
Other Scientific Names
- Antirrhinum dalmaticum L.
- Linaria dalmatica var. dalmatica
- Linaria genistifolia subsp. dalmatica (L.) Maire & Petitm.
International Common Names
- English: balkan toadflax; broadleaf toadflax
Local Common Names
- Germany: leinkraut dalmatinische
- Portugal: linaria-dalmática
- Sweden: jättesporre
- LINDA (Linaria genistifolia subsp. dalmatica)
Summary of InvasivenessTop of page
L. dalmatica is a herbaceous plant native to western Asia and south east Europe. It is of particular concern in North America where it was introduced in the late nineteenth century. It has since spread across most of the western areas of the USA and Canada (De Clerck-Floate and Turner, 2013). There it has invaded rangelands, rights-of-way and natural habitats. It is classified as noxious in many of the western states of both countries. It is also classed as invasive in South Africa. Its success may be attributed to its high specific leaf area, aggressive root system, prolific seed production and the presence of alkaloids which discourages grazing by livestock, thus allowing it to become dominant (De Clerck-Floate and Turner, 2013).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Scrophulariales
- Family: Scrophulariaceae
- Genus: Linaria
- Species: Linaria dalmatica
Notes on Taxonomy and NomenclatureTop of page
This species was named Antirrhinum dalmaticum by Linnaeus, but was moved to the genus Linaria as L. dalmatica by Philip Miller in 1768 and that name has been widely accepted. The Royal Botanic Garden Edinburgh (2015) and some other authorities however now use L. genistifolia subsp. dalmatica. The genus Linaria was previously included in the family Scrophulariaceae. Many sources still use this classification but a series of genetic studies resulted in the ‘disintegration’ of the old Scrophulariaceae such that, apart from all the parasitic members of the family being transferred to the Orobanchaceae, Linaria along with Antirrhinum and Scrophularia were transferred to Plantaginaceae (Judd et al., 1999; Olmstead et al., 2001; Judd et al., 2002; APG, 2003). The genus comprises about 100 species.
Two naturally occurring varieties are recognized, L. dalmatica var. dalmatica and L. dalmatica var. macedonica. The latter, sometimes treated as a subspecies, occurs only in Macedonia (Vujnovic and Wein, 2005). There is a further range of horticultural varieties.
A narrow leaved variant mentioned in some publications is now considered to be the related but distinct L. genistifolia, known as narrowleaf or broomleaf toadflax.
Zouhar (2003) reported that hybrids with L. vulgaris had been created in the laboratory. This was later confirmed in the wild in Montana, USA by Ward et al. (2009) with hybrids being viable and fertile.
DescriptionTop of page
L. dalmatica is a robust, glaucous, herbaceous perennial with taproots enlarged above, more or less woody, deeply penetrating (1.8 m or more into the ground), spreading by horizontal roots 5–20 cm below the surface, spreading up to 3.6 m from the plant. Adventitious offshoots from these roots are generally sterile, decumbent to weakly ascending, succulent, 3–40 per crown. Stems from the main crown are annual, 40–100 cm high, ascending to erect, more or less woody near the ground. Leaves are alternate, often in two’s or three’s on lower part of the stem, sessile, reflexed to ascending, entire, acute to acuminate at the tip, obtuse to cordate at the base, sometimes concave above, usually amplexicaul, somewhat leathery, glabrous and sometimes rugose, with 3–7 longitudinal veins on lower surface. The lower leaves are 1-5 cm long, up to 1 cm wide, linear to lanceolate; the upper leaves 3–6 cm long, 1-4 cm wide, lanceolate to very broad-ovate. Bracts are similar to upper leaves, or smaller. Flowers are in erect or nodding, simple racemes, usually loose, sometimes compact; 15–55 cm long on pedicels 1–8 mm long. Five sepals, valvate or somewhat imbricate, erect, lanceolate acute to acuminate, 0.7–1.1 cm long, 0.2–0.4 cm wide, margins entire to somewhat undulate. The corolla, including spur 3.3–4.5 cm long, light yellow to yellow, rarely nearly white; tube 6–9 mm long, the upper lip bilobate, often somewhat helmet-shaped, the lower lip trilobate; spur tapered, 1.2–1.8 cm long, straight or slightly curved; four fertile stamens adnate in pairs, didynamous 0.8–1.5 cm long, one reduced staminode; pistil bicarpellate; ovary bilaterally symmetrical ca. 2 mm diameter at anthesis, abruptly narrowed to the terminal style; style filiform, erect, stigma single, terminal, hemispherical; numerous ovules in each locule; capsule long ovoid to nearly spherical, 4–10 mm long, 4–8 mm in diameter, dehiscing terminally on each carpel. Seeds black to purplish-brown, triquetrous or somewhat compressed, muricate-rugose on the surface, 0.7–1.3 mm wide, 30–170 per locule; each seed with narrow wing on the angles. The species is morphologically highly variable (this description simplified from Vujnovic and Wein, 2005, based on original by Alex, 1962).
Plant TypeTop of page Annual
DistributionTop of page
The native distribution of L. dalmatica is restricted to the Balkan Peninsula, Turkey, Iran, Iraq, Syria and Romania. The Royal Botanic Garden Edinburgh (2015) notes that it is locally naturalized in Central Europe therefore, the records from Germany and Hungary presumably refer to introductions. It also occurs as an occasional escape from gardens in Switzerland, UK and elsewhere in Europe. It is now widely naturalized and invasive across Canada and western USA (Leo’s Dictionaries, 2015). L. dalmatica has more recently been spreading in South Africa (Invasive Species South Africa, 2015) and has also naturalized in Australia (Parsons and Cuthbertson, 1992) and in Argentina (Puntieri and Brion, 2003). As it is widely cultivated in gardens, it is likely to occur as an occasional escape in many other countries.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 10 Jan 2020
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|South Africa||Present, Localized||Introduced||Invasive||GBIF (2015)|
|India||Present||CABI (Undated)||Present based on regional distribution.|
|Iraq||Present||Native||Vujnovic and Wein (2005)|
|Syria||Present||Native||Vujnovic and Wein (2005)|
|Federal Republic of Yugoslavia||Present||Native||Royal Botanic Garden (2015)|
|France||Present, Localized||Native||GBIF (2015)|
|Germany||Present, Localized||Introduced||GBIF (2015)|
|Hungary||Present, Localized||Introduced||GBIF (2015)|
|Italy||Present, Localized||Introduced||Vujnovic and Wein (2005); Royal Botanic Garden (2015)|
|Romania||Present||Native||Royal Botanic Garden (2015); USDA-ARS (2015)|
|Switzerland||Present, Localized||Introduced||Leo's Dictionaries (2015)|
|United Kingdom||Present||Introduced||Stace (1991); Leo's Dictionaries (2015)|
|Canada||Present, Widespread||Holm et al. (1979); Vujnovic and Wein (2005)|
|-Alberta||Present||Introduced||Invasive||Vujnovic and Wein (2005)|
|-British Columbia||Present, Widespread||Introduced||Invasive||Vujnovic and Wein (2005)|
|-Manitoba||Present||Introduced||Vujnovic and Wein (2005)|
|-New Brunswick||Present, Localized||Introduced||Vujnovic and Wein (2005)|
|-Newfoundland and Labrador||Present, Localized||Introduced||Vujnovic and Wein (2005)|
|-Nova Scotia||Present, Localized||Introduced||Vujnovic and Wein (2005)|
|-Ontario||Present||Introduced||Vujnovic and Wein (2005)|
|-Prince Edward Island||Present, Localized||Introduced||Vujnovic and Wein (2005)|
|-Quebec||Present||Introduced||Vujnovic and Wein (2005)|
|-Saskatchewan||Present, Widespread||Introduced||Vujnovic and Wein (2005)|
|-Yukon||Present, Localized||Introduced||Bennett et al. (2010)|
|United States||Present||Introduced||Holm et al. (1979); Vujnovic and Wein (2005)|
|-District of Columbia||Present||Introduced||USDA-NRCS (2015)|
|-Iowa||Present||Introduced||CABI (Undated a)|
|-Montana||Present, Widespread||Introduced||Invasive||USDA-NRCS (2015)|
|-New Hampshire||Present||Introduced||USDA-NRCS (2015)|
|-New Jersey||Present||Introduced||USDA-NRCS (2015)|
|-New Mexico||Present||Introduced||USDA-NRCS (2015)|
|-New York||Present||Introduced||USDA-NRCS (2015)|
|-North Dakota||Present||Introduced||USDA-NRCS (2015)|
|-Rhode Island||Present||Introduced||USDA-NRCS (2015)|
|-South Dakota||Present||Introduced||USDA-NRCS (2015)|
|-Washington||Present, Widespread||Introduced||USDA-NRCS (2015)|
|Australia||Present, Localized||Introduced||1933||Parsons and Cuthbertson (1992)|
|-New South Wales||Present, Localized||Introduced||Parsons and Cuthbertson (1992)|
|Argentina||Present, Localized||Introduced||Puntieri and Brion (2003)|
History of Introduction and SpreadTop of page
L. dalmatica is believed to have been introduced to western USA by the late nineteenth or early twentieth century and had become naturalized in California by 1920. In Canada it was first planted in Ottawa in 1901 and was reported as naturalized in Alberta by 1933 (Vujnovic and Wein, 2005).
Risk of IntroductionTop of page
The risk of introduction of L. dalmatica continues to be high, though there must be few temperate countries to which it has not already been introduced as an ornamental. Thus the risk of spread is mainly accidental, from careless disposal of material from gardens.
HabitatTop of page
In its native range L. dalmatica is a plant of uncultivated fields, vineyards, roadsides and waste places, mainly on coarse textured soils. It may occur on limestone hills and generally favours alkaline soils. In North America, its introduced range, it occurs in similar habitats but has also invaded forest plantations, wood and herbaceous species in the genus Artemisia, pastures, rangelands and to some extent crops such as lucerne/alfalfa (Medicago sativa) (Vujnovic and Wein, 2005).
L. dalmatica has a wide temperature tolerance but on a mountain area in Canada, establishment on disturbed roadsides was limited by the low temperatures experienced at higher elevation (Polinac and Rew, 2014).
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Managed forests, plantations and orchards||Secondary/tolerated habitat|
|Managed grasslands (grazing systems)||Principal habitat||Harmful (pest or invasive)|
|Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Rail / roadsides||Principal habitat||Harmful (pest or invasive)|
|Terrestrial ‑ Natural / Semi-natural||Natural forests||Secondary/tolerated habitat|
|Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Riverbanks||Present, no further details||Harmful (pest or invasive)|
|Scrub / shrublands||Secondary/tolerated habitat|
|Deserts||Present, no further details||Harmful (pest or invasive)|
|Coastal areas||Present, no further details|
Hosts/Species AffectedTop of page
The crops affected by L. dalmatica are mainly pasture and rangeland species, but alfalfa (Medicago sativa) and forest species such as ponderosa pine (Pinus ponderosa) may also be affected.
Host Plants and Other Plants AffectedTop of page
Biology and EcologyTop of page
The chromosome number 2n = 12 has been reported for L. dalmatica (Missouri Botanical Garden, 2015).
L. dalmatica spreads both by seed and by its spreading root system. The shoots arising from the roots are described as ‘sterile’, but presumably will develop fully if separated from the parent plants.
Under laboratory conditions some seeds will germinate the same season in which produced. Germination from dry storage increases for two to three years, with a periodic low in November and a high in April. Over 90% germination is obtained with two to three year old seeds in the laboratory. In the field, germination occurs in both spring and autumn and seedlings can emerge from a soil depth of 2-2.5 cm. Seeds may be dormant for a few weeks after maturation. Thereafter they have no particular requirement (Robocker, 1970).
Seedlings which emerge in the autumn generally do not survive the following year. Most emergences occur in the spring, following stratification over winter. Cyclic alterations of 10 days stratification at 2°C and 10 days drying at room temperature for two cycles induced higher rates of germination than did any other factor. The highest germination of seeds planted at different depths in five soil textures was found to be from a depth of 1.27 cm in loamy sand (Alex, 1962). Seeds germinate from 2.5 cm in clay and loamy soils and from 5 cm in sandy soils. Seedling recruitment can be seriously reduced by plant competition (Grieshop and Nowierski, 2002).
Shoots growing from the crown flower from May and fruit by August, producing large numbers of seeds, up to 250 per capsule and up to 500,000 per plant. The flowers are self-sterile and are insect pollinated (Vujnovic and Wein, 2005). Seventeen species of bumble bee (Bombus spp.), honey bee (Apis mellifera) and the leaf cutting bee Megachile periherta were identified as pollinators, with bumble bees being most common (97% of observations) (De Clerck-Floate et al., 1997).
Physiology and Phenology
A study by Alex (1962) found that roots of seedlings penetrated downward ca. 1 cm/day during the first 31 days in fine sandy loam. Thereafter the rate was slower but roots reached a depth of 56 cm after 105 days. The total length of all roots of one 105 day old plant grown in fine sandy loam exceeded 27 m. Adventitious stem buds were present on the primary axis after 22 days of age and on the second and third order branch roots at 105 days of age. Stem buds on branch roots were mostly more than 16 cm distant from the primary axis and at depths of 2 cm to more than 10 cm below the ground surface (Alex, 1962). Once established, seedlings can flower and set seed within the first year (Vujnovic and Wein, 2005).
L. dalmatica has been shown to benefit greatly from enhanced carbon dioxide levels. In one study, at 600 ppm CO2, the biomass of L. dalmatica increased by 13 fold, seed production by 32 fold and clonal expansion by seven fold, much larger than the effects observed on the native C3 grass Pascopyrum smithii [Elymus smithii] (Blumenthal et al., 2013). Increased temperatures of 1.5/3.0°C (day/night) had little effect (Blumenthal et al., 2013). However a study by Dijkstra et al. (2010) found much less pronounced increases and emphasized the potential interactions with nitrogen and water levels.
The average life of a plant is about three years. The life of a stand varies and depends on the interactions of the plant's growth habits with environmental factors. A stand may disappear within three years under severe competition. However the development of floral stems from secondary crown points on lateral roots may prolong or sustain the stand beyond the life of the original plants (Robocker, 1974).
Nitrogen addition has a strong positive effect on plant performance, with a two fold increase in both biomass and seed production (Jamieson et al., 2010).
In North America, L. dalmatica is associated with pastures and rangelands dominated by Bromus tectorum, B. japonicus, Stipa comata, Koeleria cristata [Koeleria pyramidata], Festuca idahoensis and Artemisia tridentata (Vujnovic and Wein, 2005).
L. dalmatica is favoured by high water and nitrogen availability, but is relatively unpalatable to cattle. Cover of L. dalmatica was high on steeper slopes, particularly those with southern aspects (Jamieson et al., 2010). The beneficial effects of nitrogen on L. dalmatica can be neutralized by addition of labile carbon to the soil (Blumenthal, 2009).
Wilson et al. (2005) indicate that L. dalmatica is particularly favoured in areas with dry summers. Nevertheless, snow can be highly beneficial to L. dalmatica, apparently in terms of providing high moisture during its establishment phase (Blumenthal et al., 2008).
Post wildfire conditions in high severity burned areas favour increased density, cover, reproduction and spread of L. dalmatica. Whilst native species richness may be reduced, suggesting that the invasive species would persist, at least in the short term, at the expense of natives (Dodge et al., 2008). L. dalmatica was also found to benefit from prescribed fire in a rangeland situation (Jacobs and Sheley, 2003).
ClimateTop of page
|BS - Steppe climate||Preferred||> 430mm and < 860mm annual precipitation|
|BW - Desert climate||Tolerated||< 430mm annual precipitation|
|Cf - Warm temperate climate, wet all year||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year|
|Cs - Warm temperate climate with dry summer||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers|
|Ds - Continental climate with dry summer||Preferred||Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)|
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Mean annual temperature (ºC)||-5|
|Mean minimum temperature of coldest month (ºC)||-25|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Dry season duration||0||8||number of consecutive months with <40 mm rainfall|
|Mean annual rainfall||300||1500||mm; lower/upper limits|
Rainfall RegimeTop of page Bimodal
Soil TolerancesTop of page
Special soil tolerances
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Brachypterolus pulicarius||Herbivore||Inflorescence||to genus||USA and Canada|
|Calophasia casta||Herbivore||Leaves||not specific|
|Calophasia lunula||Herbivore||Leaves||not specific||USA and Canada|
|Chrysolina gypsophilae||Herbivore||to genus|
|Chrysomela rossia||Herbivore||not specific|
|Eteobalea intermediella||Herbivore||Roots||to species||USA and Canada|
|Eteobalea serratella||Herbivore||Roots||to species||USA and Canada|
|Mecinus janthiniformis||Herbivore||Stems||to genus||USA and Canada|
|Mecinus laeviceps||Herbivore||Stems||to genus|
|Mecinus peterharrisi||Herbivore||Stems||to genus|
|Rhinusa antirrhini||Herbivore||Seeds||to genus||USA and Canada|
|Rhinusa linariae||Herbivore||Roots||to genus||USA and Canada|
|Rhinusa neta||Herbivore||Seeds||to genus||USA and Canada|
|Rhinusa rara||Herbivore||Stems||to species|
Notes on Natural EnemiesTop of page
The natural enemies of L. dalmatica have been well studied as a part of efforts to achieve biological control. Potential biocontrol organisms have included Calophasia lunula, Mecinus janthiniformis, Eteobalea intermediaella, Rhinusa neta, R. linariae and R. antirrhini. Recent studies include the stem boring weevils M. laeviceps and M. peterharrisi and the stem-galling weevil R. rara.
Means of Movement and DispersalTop of page
Seeds of L. dalmatica mainly fall near the parent plant but may also be spread to some extent by wind (Robocker, 1974). L. dalmatica can also reproduce vegetatively by the production of new shoots from roots and root fragments.
Some dispersal can occur locally via grazing by cows and deer. It has been suggested that seed can remain viable after ingestion and egestion (Robocker, 1974).
Accidental introduction can occur on a local basis by contaminated cultivation equipment spreading seeds or root fragments.
Intentional introductions have readily happened, as L. dalmatica has been imported into a number of countries for ornamental purposes.
Pathway CausesTop of page
Pathway VectorsTop of page
Impact SummaryTop of page
|Fisheries / aquaculture||None|
Economic ImpactTop of page
L. dalmatica asserts an economic impact on productive grassland and rangelands in Canada and the USA. This species becomes dominant as a result of vigorous vegetative growth and competition, especially under conditions of overgrazing and drought, but also perhaps as a result of allelopathy via the action of iridoid glycosides under low nitrogen conditions (Jamieson et al., 2013). Jacobs and Sing (2006) indicate that grass production can be 2.5 times lower in dense infestations of L. dalmatica than in similar areas without the weed. No other quantitative estimates of damage have been seen. It is rarely reported in other crops, except in lucerne/alfalfa (Medicago sativa) and in pine plantations (Pinus species) (Vujnovic and Wein, 2005).
De Clerck-Floate and Turner (2013) refer to its potential toxicity to livestock, though other authors generally suggest that they avoid it. Sing and Peterson (2011) discuss in detail the various metabolites in L. dalmatica and their potential for toxicity to animals. This species can also be a reservoir for crop pathogens including cucumber mosaic virus and it can have a tendency to increase soil erosion.
Environmental ImpactTop of page
Impact on Biodiversity
Although L. dalmatica has become dominant in a range of ecologies in North America, including natural habitats, there have been no reports of the serious effects on biodiversity or individual endangered species. Sing and Peterson (2011) make detailed attempts to quantify the environmental risks from L. dalmatica and the levels of the weed which would cause significant reductions. They concluded that more than six L. dalmatica plants per 10 m2 could cause a 25% reduction in Hedeoma diffusum. A dry weight of 1,163 kg/ha L. dalmatica is the threshold beyond which there could be 25% reduction in cool season grasses.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Highly adaptable to different environments
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Pioneering in disturbed areas
- Long lived
- Fast growing
- Has high reproductive potential
- Has propagules that can remain viable for more than one year
- Reproduces asexually
- Has high genetic variability
- Ecosystem change/ habitat alteration
- Host damage
- Monoculture formation
- Negatively impacts agriculture
- Negatively impacts forestry
- Reduced native biodiversity
- Threat to/ loss of native species
- Competition - monopolizing resources
- Competition - smothering
- Pest and disease transmission
- Highly likely to be transported internationally accidentally
- Highly likely to be transported internationally deliberately
- Difficult to identify/detect as a commodity contaminant
- Difficult/costly to control
UsesTop of page
Due to its showy flowers, L. dalmatica has been widely cultivated as an ornamental in gardens. There is an early record of it being so used in Italy before 1594 and by the nineteenth century it was present in England and by the end of that century in the USA (Vujnovic and Wein, 2005). It is still commercially available as seed or as root pieces in Europe and Asia. Exotic toadflaxes including L. dalmatica also continue to be sold commercially in the USA, although this is illegal in a number of states where they are listed as noxious (Wilson et al., 2005).
Uses ListTop of page
- Sociocultural value
- Propagation material
- Seed trade
Similarities to Other Species/ConditionsTop of page
L. dalmatica is quite distinct from the co-occurring L. vulgaris, which has narrow strap like leaves. L. genistifolia, which also occurs in the USA, also differs from L. dalmatica in its much narrower leaves and relatively small corolla (2-5 cm), while the seeds are without a winged margin.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
L. dalmatica is listed as noxious in Arizona, California, Colorado, Idaho, Minnesota, Montana, Nevada, North Dakota, New Mexico, Oregon, south Dakota, Utah, Washington and Wyoming, USA (USDA-NRCS, 2015). In British Colombia, Canada, it is listed as noxious in Alberta and Manitoba (De Clerck-Floate and Turner, 2013).
Cultural Control and Sanitary Measures
It is well recognized that L. dalmatica is quick to exploit gaps and weaknesses in established grass stands. It can be kept out of areas by maintenance of a dense healthy stand. Grasses may vary in their effectiveness and in one study of grasses to suppress L. dalmatica, the greatest reduction (95%) was found with Elymus lanceolatus (Rose et al., 2001). However, once established it may not be readily suppressed by newly sown grasses. Early detection is vital for the control of new infestations.
Mowing is relatively ineffective for controlling L. dalmatica as the weed can readily recover from the root systems and the removal of competition from other vegetation may allow it to increase. Similarly burning may encourage growth rather than suppress it. In crop land intensive cultivation for at least two years with at 8-10 cultivations in the first year may be required. Hand pulling can prevent seeding but only annual grubbing and pulling over a 10-15 year period can control it fully (Vujnovic and Wein, 2005).
L. dalmatica has been the subject of a number of biological control programmes. According to De Clerck-Floate and Turner (2013), five insect biocontrol agents have been tested and intentionally introduced into Canada for control of L. dalmatica. The first field release took place in 1963.
Of the five insects released, three have established on L. dalmatica. These include the seed capsule weevil Rhinusa antirrhini, the defoliating moth Calophasia lunula and the stem boring weevil Mecinus janthiniformis. The latter had previously been referred to as ‘M. janthinus’ but differing results from different populations of this ‘species’ led to the realisation that two species were involved. Only M. janthiniformis is effective on this L. dalmatica while L. janthinus is effective on L. vulgaris (Toševski et al., 2011). Toševski et al. (2013) have now described a fast and accurate way of distinguishing the two Mecinus species haplotypes using PCR-RFLP diagnostic assay of the mitochondrial cytochrome oxidase subunit II (COII) gene.
R. antirrhini has established well in British Colombia, Canada and populations are increasing. It is however uncertain whether this seed feeding agent can have a significant impact on the weed (De Clerck-Floate and Turner, 2013).
In Canada, Calophasia lunula has only become established in southern British Colombia and not at all in Alberta, apparently due to low temperatures (De Clerck-Floate and Turner, 2013). Jamieson et al. (2010) found that C. lunula has a mechanism to de-activate the iridoid glycosides, defence mechanisms, in L. dalmatica but ‘M. janthinus’ does not.
M. janthiniformis is by far the most successful biocontrol agent released in Canada. Damage is caused by both adults and larvae and conspicuous reductions in the weed have been recorded. Results are less successful in Alberta almost certainly due to severe winter temperatures. Some disappointing results may also be due to the wrong Mecinus species being released. Weed and Schwarzländer (2014) suggest that the impact of M. janthiniformis may vary considerably due to site specific variation in rainfall and density dependent processes. As a result alternative control methods should be prioritized in areas where herbivore impact is expected to be low. Studies have recently started on two additional Mecinus species, M. laeviceps and M. peterharrisi (Toševski et al., 2016). A petition for the introduction of the stem-galling weevil R. rara n North America is pending.
Two species introduced but not proving successful are the root galling weevil R. linariae which proved to have a preference for L. vulgaris and is no longer being exploited and the root moth Eteobalea intermediella which established in 1998 but had died out by 2002 and is no longer being used (De Clerck-Floate and Turner., 2013). The related E. serratella was thought by Quarles (2007) to be having an impact on L. dalmatica, but Shelton (2015) notes that L. dalmatica is a relatively poor host for this species and it appears that it is no longer of interest.
Grubb et al. (2002) suggested that the naturally occurring flower feeding beetle Brachypterolus pulicarius might prove to be an important component in the integrated weed management of L. dalmatica but that the adults show a distinct preference for L. vulgaris and its further distribution in North America was not recommended (MacKinnon et al., 2007). The seed capsule weevil R. neta also occurs widely in British Colombia, Canada but is not being actively distributed (De Clerck-Floate and Turner 2013).
Wilson et al. (2005) provide extremely detailed and valuable information on the biology of the biocontrol organisms and the planning, implementation and monitoring of biological control programmes against both L. dalmatica and L. vulgaris.
Phenoxy-propionic herbicides are superior to phenoxyacetic herbicides in controlling L. dalmatica. Satisfactory control can be obtained with fenoprop. Rates of fenoprop required to check or to control the plant did not injure perennial grasses. Dicamba has also been effective however it is resistant to triclopyr and fluroxypy (Vujnovic and Wein, 2005).
Picloram can be effective when applied at various stages of growth, but granules applied to the soil in the autumn can be more effective than a foliar application at the same rate in spring (Vujnovic and Wein, 2005). A combination of fenoprop and picloram has also provided control (Robocker, 1968).
Aminocyclopyrachlor (140 and 280 g ae ha-1) and aminocyclopyrachlor+chlorsulfuron (140 g/ha+53 g/ha) gave second year control; chlorsulfuron at the dormant stage (105 and 158 g/ha) and aminopyralid at the rosette stage (245 g/ha) also gave 2 years of control. The treatments had only minor effects on grass species (Kyser and DiTomaso, 2013).
Herbicides recommended by USDA Forest Service (2012) for use in non-crop areas include imazapic, glyphosate, rimsulfuron, sulfometuron and chlorsulfuron.
Quarles (2007) suggests that integrated control of L. dalmatica could involve combinations of clean cultivation, pulling, mowing, burning, grazing, competitive planting, using biological control agents and herbicides. Suggestions for integrated control strategies are also made by the USDA Forest Service (2012). Suggestions include checking hay and straw for the presence of seed, feeding certified weed-free hay pellets to horses, combining control methods and ensuring that follow up treatment is carried out to treat plants that are missed.
There are indications that the reduction of L. dalmatica in mixed natural plant communities has tended to encourage the invasion of other equally undesirable weedy species such as Bromus tectorum and Centaurea maculosa [Centaurea podospermifolia].
ReferencesTop of page
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ContributorsTop of page
13/12/2016 Updated by:
André Gassmann, CABI-CH, Switzerland
12/06/2015 Original text by:
Chris Parker, Consultant, UK
Distribution MapsTop of page
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