Dipsacus fullonum
(common teasel)

D. fullonum is a biennial plant native to North Africa, Europe and West Asia. It has been introduced to North and South America, Australia and New Zealand. Although mainly a weed of pastures and roadsides, it sometimes also grows in natural communities and forms a large basal rosette of leaves in the early stages of growth. This rosette of leaves can cover a large area and shade other ground-dwelling plants nearby (Weeds of Australia, 2013). Donaldson (2002) claimed that D. fullonum ‘is spreading rapidly throughout the United States except in the northern Great Plains,’ and in the USA it has been classified as a noxious weed in Colorado, Iowa, Missouri and New Mexico (USDA-NRCS, 2013).

D. fullonum is native to North Africa, Europe and West Asia. It has been introduced to USA, Canada, Argentina, Bolivia, Ecuador, Uruguay, Australia and New Zealand.

The seedheads of D. fullonum are often used in dried flower arrangements and the transfer of seeds still trapped in the seedheads from country to country or within countries could be a source of new introductions. There are many sites online selling seeds and this is another possible high risk pathway for introductions. Introduction in contaminated crop seed is unlikely, because D. fullonum seed ought to be identified in phytosanitary searches.

Weber (2003, cited in Gucker, 2009) reported that D. fullonum is found in similar habitats in both its native and introduced ranges, including riparian areas, meadows, grasslands, savannahs, forest openings and disturbed sites. It is also found on the upper reaches of salt marshes (Badger and Ungar, 1994), its tolerance of saline conditions playing a part in its occupation of roadsides where salt is used for de-icing (Beaton and Dudley, 2004). In Canada, Werner (1975b) reported that the species grows on a variety of soils from sandy soils with abundant moisture to heavy clays in poorly drained areas. In New Zealand, Popay et al. (2010) described its habitat as roadsides, abandoned pasture, cultivated land, riverbeds and waste places.

The invasion of D. fullonum in New Mexico may adversely affect Cirsium vinaceum, an endemic thistle that is federally listed as threatened (Huenneker and Thomson, 1995). In Australia it sometimes grows in natural communities, where it forms a large basal rosette of leaves that can cover a large area and shade nearby ground-dwelling plants (Weeds of Australia, 2013).

Genetics

2n = 18 (Clapham et al., 1962; Werner, 1975b).

Reproductive Biology

The flowers are protandrous, the stamens ripening before the pistil. Flowers are visited by bumblebees (Bombus spp.) and other smaller bees which collect pollen and become covered in it (Werner, 1975b). The same author found that if cross-pollination was prevented, only 4% of seeds were viable, compared with 70% or more with cross-pollination.

Within a flower head, flowers first mature in a ring about half-way up the head. One ring then moves upwards and another downwards over several weeks (Werner, 1975b). Although in the related D. laciniatus the primary head completed flowering within four days after initial flowering, it took 45 days before 90% of all the heads on the plant had flowered (Bentivegna and Smeda, 2011).

Werner (1975b) observed that the number of seeds per inflorescence was governed by the length of the core of the flowering head. The average number of potential seeds per head was about 855 and the number of fertilised seeds was estimated at about 727. The same author found that the number of inflorescences per plant was usually 3-9, but sometimes as many as 35.

In the related D. laciniatus, germinable seed was observed only nine days after flowering (Bentivegna and Smeda, 2011).

Physiology and Phenology

In Canada, seeds are dispersed in autumn but few seedlings are found before the next spring (Werner, 1975b). Seeds harvested in October germinated readily, with over 70% germination, and with no apparent need for freezing or stratification. Seeds stored dry for up to six years showed only a slight decline in viability over that time, although older seeds took longer to germinate.

In the English midlands, seedlings of D. fullonum started to emerge soon after sowing in autumn and continued to emerge throughout winter and for most of the following year (Roberts, 1986). In later years flushes occurred after cultivation of the surface soil, especially in April (spring) and to a much lesser extent in September, but sporadically at other times, and seedlings continued to emerge for as long as the five years of observations. Werner (1975b) similarly found that seeds germinated mainly from early April to June, although a few germinated in early September. Bentivegna and Smeda (2011), working with the related species D. laciniatus in Missouri, USA, found that 95% of germination occurred in April and October.

D. fullonum produces a stout taproot, which can be more than 0.6 m long and 2.5 cm thick at the crown (Gucker, 2009). The plant first develops a rosette which can be 51 cm or more across (Werner, 1975c). Once the rosette is large enough (occasionally after one season, but sometimes after several years) and temperature and day length conditions are right, the tall flowering stem begins to grow out of the old rosette base (in May in Canada) and reaches its full height of up to 2-3 m (in July in Canada) (Werner, 1975b). Flowers are continually produced from July to early September: seeds mature in the head and are dispersed from September to late November. The seeds germinate from early April to early June and the rosettes that develop continue to increase in size until late autumn (Werner, 1975b). During winter the rosette leaves often become brownish-green and some may die.

Beaton and Dudley (2004) found that populations of D. fullonum from roadsides in Ontario, where they are exposed to salt used for winter de-icing, were more tolerant of salinity than old-field populations not exposed to salt. The authors speculated that this tolerance was the result of a maternal environmental effect rather than a genetic one. The same authors (Beaton and Dudley, 2007) explored this further and deduced that D. fullonum has two distinct salt-tolerance strategies: a) osmotic stress tolerance, as a result of the parent plant modifying the chemical composition of the seeds to confer salinity tolerance during germination, and b) an inherent ability to tolerate high salinity levels. In further work, Beaton and Dudley (2013) found that families of D. fullonum from roadside populations showed greater tolerance of both high salinity and drought than families from old-field populations, but that no maternal family had tolerance to both drought and salinity, suggesting that the two traits are separate in this species.

Longevity

Seeds can survive in the soil for at least 5 years (Roberts, 1986). Plants of D. fullonum can remain as rosettes for between two and at least four years in Canada, where most seedlings emerge in autumn (Werner, 1975b). Length of survival depended on the kind of plants present in the community. In fields where cover was 65-72% of Elymus repens plants grew from seedlings to flowering in two years: in habitats where the other vegetation was taller flowering could take place after three or four years (Werner, 1975c). In one field with an understorey of herbaceous perennials and a shrub cover of over 50%, all rosettes died within five years without flowering.

Population Size and Structure

Werner (1975b) said that even in large populations of D. fullonum individual plants are usually spaced 0.5 to 1.5 m apart, although in one population in Michigan the author observed about 13 flowering stalks and 7 mature rosettes per square metre. The same author suspected that teasel numbers fluctuate greatly and that the spread of a population is relatively slow by comparison with some other weeds, as generation time is longer than one year and no vegetative reproduction occurs. The author also found that in a range of fields where seeds were sown in the winter of 1968/1968 and plants then established, the annual number of seeds produced was about the same in 1973, regardless of the number of plants (whose ground cover ranged from 2.3% to almost 40%) or the age of the plants.

Nutrition

Darwin (1877) suggested that the filamentous hairs on the leaves of D. fullonum may have the function of absorbing nitrogenous fluids ‘accumulating within the connate leaves of the plant.’ He speculated that the source of the nitrogen was ammonia in the rain and dew. The opposite leaves are connate, joined together at the base to form a cup-shaped structure in which rain or dew collect. Christy (1923) suggested that the purpose of these ‘cups’ is to serve as a mortuary for insects (and other invertebrates) and that the plant somehow benefits from the presence of these dead creatures, a supposition partly tested by Shaw and Shackleton (2011), who found that seed production and the seed mass:biomass ratio was greater in plants that were ‘fed’ maggots. As the authors suggest, the result needs duplication, and also begs other questions, such as: are insects attracted to the fluid, how are they digested, and do plant structures cause insects to fall into the fluid?

Associations

D. fullonum is found in many different places and thus associates with many other plant species. Werner (1975b) reported that it and other species of Dipsacus are found mainly (in Canada) in the later stages of succession of abandoned crop or hay fields, on roadsides, along irrigation ditches and creeks, and in other disturbed areas. The author added that both the rosette and flowering stages usually grow in open sunlight with leaf surfaces above dead plant litter or other vegetation.

Environmental Requirements

The largest plants are found when conditions are such that soil moisture is relatively high throughout the growing season (Werner, 1975b). D. fullonum does not grow in areas with prolonged cold periods.

Sforza (2004) and Rector et al. (2006) searched for natural enemies of D. fullonum and D. laciniatum by surveying literature and conducting field searches in their native ranges. These authors found 102 species of insects, 27 fungi, three mites, one nematode and two viruses damaging these species, of which six species (three insects, one mite and two fungi) were considered worthy of further assessment. These were: Chromatomyia ramosa (Hendel) (Diptera: Agromyzidae), Longitarsus strigicollis Wollaston (Coleoptera: Chrysomelidae), Epitrimerus knautiae Liro (Acarina: Eriophyiidae), Euphydryas desfontainii (Godart) (Lepidoptera: Nymphalidae), Erysiphe knautiae Duby (Erysiphales: Erysiphaceae) and Sphaerotheca dipsacearum (Tul. and C. Tul.) (Erysiphales: Erysiphaceae).

Dugan and Rector (2007) conducted a preliminary survey of seed mycoflora of D. fullonum in Washington State in the Pacific Northwest of the USA. In symptomatic seed they found a high rate of colonisation by Cladosporium and Alternaria spp., both of which can cause damping off in seedlings, and, in asymptomatic seed, a high rate of colonisation by Aureobasidium pullulans. However, they did not succeed in infecting D. fullonum seedlings with conidial suspensions of any of these fungi.

The confusion over the names D. fullonum, D. sylvestris and D. sativus is discussed in Notes on Taxonomy and Nomenclature. D. sativus has very stiff bracts ending in recurved spines, wheras D. fullonum has flexible bracts ending in straight spines (The Jepson Herbarium, 2914). 

D. laciniatus, slashed teasel, is also found in North America, but is not so widely naturalised. It has irregularly-cut pinnatifid leaves, white flowers and shorter involucral bracts which are not longer than the florets (Werner, 1975b).

Hybrids occur between D. fullonum and D. laciniatus (Gucker, 2009; Natural History Museum, 2013) and between D. fullonum and D. sativum (Natural History Museum, 2013).

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.

SPS Measures

Border inspections ought to prevent D. fullonum spreading to new countries, but deliberate or accidental transmission of seed heads containing viable ripe seed could occur. Seeds are also freely available on the internet and this is another possible source of newly introduced seeds.

Physical/Mechanical Control

Although cutting leaves and stems to ground level encourages the taproot to resprout, repeat cuttings before flowering effectively eradicates a population (Werner, 1975b), although new seedlings could emerge from seeds in the soil. However, Gucker (2009) cited cases where repeated mowing or cutting had little effect on populations. Cheesman (1998) found that some stems cut before flowering regrew but produced significantly fewer flowerheads than uncut plants. Stems cut during or after flowering produced no new seedheads, and seeds in flowerheads cut at or immediately after flowering failed to germinate. In small infestations flowering stalks could be cut and the cut flowerheads removed from the site (Glass, 1991). Some authors have suggested cutting the plants well below the surface and removing the seedheads (Glass, 1991; Donaldson et al., 2002) as a method of control.

A well-managed uniform pasture ought to prevent invasion of new seedlings. Litter from Agropyron (now Elymus) repens reduced the germination of D. fullonum, possibly as a result of allelopathic chemicals in the litter (Werner, 1975d).

Biological Control

The search is ongoing for biological controls for D. fullonum and D. laciniatum in the USA (Sforza, 2004; Rector et al., 2006). These authors searched for natural enemies of D. fullonum and D. laciniatum by surveying literature and conducting field searches in their native ranges, and identified 102 species of insects, 27 fungi, three mites, one nematode and two viral natural enemies for screening as candidates for biological control. Highest priority for initial study has been assigned to two insects that attack the rosette – the chrysomelid flea beetle Longitarsus strigicollis and the agromyzid fly Chromatomyia ramosa (Rector et al., 2005).

Chemical Control

Glass (1991) suggested using glyphosate or 2,4-D applied to rosettes in late autumn or early spring. Glyphosate is not selective and will kill any green plants it touches; 2,4-D kills or damages many broadleaved species but does not harm most grasses. Donaldson (2002) also suggested using 2,4-D, and also reported that 2,4-D + dicamba or triclopyr + clopyralid, chorsulfuron or metsulfuron can be effective when applied to actively growing rosettes.

Control by Utilization

Gucker (2009) indicated that mice and voles may consume seeds of D. fullonum in the USA, and also reported (citing several observers) that California quail, ring-necked pheasants, crossbills, finches and blackbirds all feed on the seeds. Livestock grazing of either rosettes or flowering plants seems unlikely because of the prickly nature of the leaves and heads.

22/06/13: Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research.