More info for the terms: association, density, fen, fire management, forbs, frequency, fresh, invasive species, natural, nonnative species, prescribed fire, presence, restoration
Impacts: Although few studies indicate the methods by which teasel impacts its nonnative habitats, several studies report that teasel may develop large monocultures [90], negatively impact riparian area integrity [74], and occupy habitats important to sensitive or threatened plant species [78]. However in Michigan old fields, diversity and species richness were higher in early-seral old-fields with common teasel than in those without [97].
Several sources provide anecdotal information about teasel impacts. In northwestern North America, Taylor [85] describes common teasel as "truly noxious" in moist areas and capable of displacing native vegetation. Weber [90] notes that monotypic teasel stands can exclude other vegetation and may restrict wildlife movements. In a review, Glass [29] indicates that cut-leaved teasel is "more aggressive" than common teasel and that cut-leaved teasel has "severely threatened" the "natural quality" of several "high quality" prairies, savannas, seeps, and sedge meadows in northern and central Illinois. In these parts of Illinois, cut-leaved teasel spread, since 1990 or earlier, was substantial (Solecki personal observation as cited in [80]). For more on the localized spread of teasel, see Local distribution changes.
Although several researchers and land managers consider teasel a potentially invasive nonnative species, common teasel was not a high-priority species in a list ranking those species thought to seriously reduce biodiversity. Common teasel was listed number 80 in a prioritized list of 81 nonnative invasive species in natural Canadian habitats [13]. However, several morphological and reproductive characteristics suggest teasel has the potential to be a problematic invasive species. A review reports that teasel's thick, well-developed taproot allows for substantial nutrient and water storage, which increases the potential for regrowth after damage and/or survival of inclement conditions. Barbs and spines defend teasel against herbivory and may focus grazing or browsing on unprotected associated vegetation. High levels of seed production, high seed germinability, and little dormancy in fresh seed allows for rapid establishment in open areas, and death of the parent provides habitat for future seedling recruitment [80].
Potential allelopathy: The leachate from common teasel seeds may affect germination of other common teasel seeds and may vary between common teasel populations. When seeds from old-field and roadside populations in Ontario, Canada, were germinated together, the initial root growth of old-field seeds was significantly shorter in the presence of roadside seeds than in the presence of other old-field seeds (P=0.02). Researchers found that roadside seeds leached significantly greater levels of sodium ions than old-field seeds (P<0.01) [7].
Riparian biotic integrity: In a survey of western riparian habitats, common teasel occurred more often in disturbed than undisturbed riparian areas (P<0.001). Riparian area biotic integrity, as measured by macroinvertebrate and vertebrate aquatic communities, was lower when common teasel was present than when it was absent (P<0.05) [74]. Researchers did not distinguish the degree to which common teasel or past disturbance was impacting biotic integrity.
Other vegetation: In the early successional development of old fields in Michigan, the introduction of common teasel led to increased species richness overall, but the abundance of some native and nonnative forbs decreased with the introduction. In fields in Kalamazoo County, Michigan, species richness was significantly greater in fields with common teasel than in fields without (P<0.005). Typically species number increased in each of the 3 years after common teasel seeding. The introduction of common teasel increased the diversity in 87.5% of old-field plots. When common teasel reached flowering stage, community productivity was significantly greater in common teasel fields than in control fields (P=0.027) [99]. Although diversity and species richness were higher in old fields with common teasel, desirability or nativity of the additional species was not assessed. During observations made up to 5 years after the introduction of common teasel in Michigan old fields, Werner [97] noted that abundance of the native hairy white oldfield aster (Symphyotrichum pilosum), native eastern daisy fleabane (Erigeron annuus), and nonnative Canada thistle (Cirsium arvense) decreased with increased common teasel abundance. However, another species, garden yellowrocket (Barbarea vulgaris), a nonnative winter annual, established in spaces created by dead common teasel plants and was restricted to common teasel fields [97].
In New Jersey and New Mexico, studies indicate that teasel populations may monopolize habitats utilized by threatened or endangered species. In a limestone fen in New Jersey's Warren County, dense teasel populations occupy habitats important to 2 state endangered species, American globeflower (Trollius laxus) and water speedwell (Veronica anagallis-catenata) [78]. Over a 3- to 4-year period in central New Mexico, density of and area occupied by common teasel increased in habitat of the threatened Sacramento Mountain thistle. In about 20% of quadrats, common teasel and Sacramento Mountain thistle occurred within a 1 m² area. In several quadrats, seedling densities of common teasel exceeded 150 seedlings/m², whereas Sacramento Mountain thistle seedling densities rarely exceeded 20/m². A greenhouse study established that the 2 species had similar germination requirements, but that the germination of Sacramento Mountain thistle was significantly lower in dark than in light (P<0.05), while common teasel germinated equally well in dark and light conditions. When plant growth was monitored, Sacramento Mountain thistle was significantly smaller in pots with common teasel than in pots with only itself (P=0.02). Common teasel growth was unaffected by the presence of Sacramento Mountain thistle [42]. Grazing in Sacramento Mountain thistle habitats may foster establishment and persistence of common teasel [82].
Control: Several sources indicate that teasel control should focus on decreasing the density of established plants while preventing seed production and dispersal [22,80]. Early detection of teasel populations reduces the effort necessary to reduce established plant densities [80]. Based on demography studies, researchers suggest that control of short-lived, rapidly growing nonnative plants should focus on limiting growth and reproduction rather than trying to impact survival of established plants [71].
Fire: For information on the use of prescribed fire to control this species, see Fire Management Considerations.
Prevention: Maintenance or restoration of wetlands, minimizing soil disturbances, and improving public education and behaviors could help to prevent teasel introductions and spread. When areas of Swavesey in Camridgeshire, England, were drained, common teasel established within 3 years in the lowland meadow [38]. Teasel is often described in association with disturbed sites. Minimizing disturbances may decrease its establishment and spread [22]. Changing human behaviors that encourage teasel seed dispersal could prevent teasel seed spread; however, from 1995 and 2000, common teasel seeds were available for sale in US plant nurseries [56].
Physical or mechanical: While some teasel plants may be killed by cutting or mowing, many sprout and some may still produce seed [29]. Available literature (as of 2009) suggests that common teasel may be more susceptible to cutting than cut-leaved teasel. Werner (Werner unpublished data cited in [95]) reported that repeated cutting eliminated common teasel stands, but no details were provided about the timing, frequency, or disposal methods used. Typically, researchers and land managers suggest that belowground cutting is most effective [29,90], but plants may still regenerate [40]. Reduced seed production and plant death are most likely if plants are cut just before or as they flower [33]. However, viable seeds may be produced on cut stems, making disposal of flowering stems in cut areas important to successful teasel control [79].
Although common teasel is not often the target of control efforts in the United Kingdom, Cheesman [14] conducted an experiment in field boundaries that provides potentially useful control information. Common teasel stems were cut to height of 2 inches (5 cm) when they had flower buds, were beginning to flower, or producing mature seeds. Flower head production on the regrowth of stems cut at the bud stage was 78% to 94% lower than that of uncut common teasel stems. Twenty percent of plants regrew following cutting at the flowering stage but no cut stems produced seed. Stems cut when seed was maturing produced no new growth in the treatment or following year [14].
In the Loda Cemetery Prairie in Illinois, managers cut cut-leaved teasel stems annually for 7 years and burned sites biennially. Cutting occurred when flower buds were present but before peak flowering. Cut stems were left on the treatment site. Cut-leaved teasel populations were not reduced by this management (Harty and White personal communication cited in [79]). Seeds from the cut stems germinated. After 1 and 7 months of room-temperature storage, 41% and 97%, respectively, of the seeds from cut stems germinated [79].
Mowing failed to control cut-leaved teasel in the Mascoutin Recreation Area of DeWitt County, Illinois. When patches of similar size and plant density were mowed or undisturbed, the size of mowed patches increased by 33 m², while control patches increased by 4.2 m². Seed dispersal by mowing was considered the reason for increased patch size [67].
Biological: A review reported that moderate to heavy grazing can limit teasel establishment [33]. It is unclear whether grazing and/or trampling restrict establishment. In 2006, insect, fungal, and viral biocontrols were being evaluated for potential biological control of teasel. Researchers predicted that organisms attacking the taproot or rosette may provide the most effective control [73].
Chemical: Early-spring or late-fall herbicide applications may allow managers to better target teasel plants, since much of the associated vegetation is dormant at this time [81]. In Missouri, several herbicides used to treat cut-leaved teasel provided some initial control. Residual herbicides did not prevent the next year's seedling emergence. In many cases, emergence on treated plots exceeded that on untreated plots. Openings created through herbicide-induced mortality may have provided suitable sites for germination [8]. Survival of other plants on the site may have offered protection for seedlings and thus provided for seedling survival. See germination, seedling establishment, and the case study summary for additional information on these topics.
Integrated management: Burning or mowing to expose rosettes before mechanical or chemical treatments may increase effectiveness [33].
