Great Mullein (Invasive Exotic Plants of North Carolina)

Great Mullein

Verbascum thapsus

Summary ⁸

Verbascum thapsus (great mullein or common mullein) is a species of mullein native to Europe, northern Africa and Asia, and introduced in the Americas and Australia.

Ecological threat in the united states ⁹

Common mullein threatens natural meadows and forest openings, where it adapts easily to a wide variety of site conditions. Once established, it grows more vigorously than many native herbs and shrubs, and its growth can overtake a site in fairly short order. Common mullein is a prolific seeder and its seeds last a very long time in the soil. An established population of common mullein can be extremely difficult to eradicate.

Impacts and control ¹⁰

More info for the terms: capsule, cover, density, fire management, forbs, invasive species, litter, natural, nonnative species, presence, restoration, root crown, shrubs, succession

Impacts: In many areas and vegetation types, common mullein is a short-lived member of disturbed communities whose abundance decreases with increased time since disturbance. In 1999 the California Invasive Plant Council listed common mullein as a "wildland pest plant of lesser invasiveness" because its spread and degree of habitat disruption were less than the area's other pest plants [20]. As of 2004, a Forest Service report lists common mullein as a widespread nonnative species that is generally restricted to disturbed sites and not especially invasive in undisturbed habitats in the eastern United States [138]. However, in parts of California and in Hawaii, common mullein may form dense and persistent populations [7,16,31,144].

In moist meadows and drainages of California's Mono Lake and Owens Valley, common mullein populations can be abundant. Common mullein has also colonized intact and undisturbed meadows in this area. In the western Sierra Nevada, common mullein establishes almost immediately following fire. Although common mullein is eventually replaced by regenerating shrubs, it may restrict the establishment of native early-seral forbs and grasses and disrupt normal succession in the Sierra Nevada [16].

High density common mullein populations are common in Hawaii. Common mullein has colonized habitats from near sea level to near the Mauna Kea summit at 15,080 feet (4,600 m) [7,33]. As of a 1990 review, common mullein occupied over 2,000 kmÂ² area. Densities as high as 190 plants/100 mÂ² have been reported on disturbed areas of Mauna Kea, although common mullein is also widely established and often abundant and persistent in relatively undisturbed subalpine grasslands dominated by alpine hairgrass (Deschampsia nubigena), subalpine woodlands dominated by ohia lehua (Metrosideros polymorpha), and in alpine desert communities [7,31,144]. Common mullein plants in Hawaii frequently form an odd-shaped, fasciated inflorescence capable of seed production 3 times that of normal flowers (Daehler, unpublished data, cited in [33]).

Common mullein is also considered disruptive to the recruitment of native flora in Hawaii [33]. In subalpine vegetation on Mauna Kea, removal of common mullein from experimental plots increased the cover of all grasses. Mauna Kea subalpine vegetation is species poor, and there are abundant bare sites. Grass cover was significantly greater (P<0.05) on sites where common mullein and associated litter were removed for all 3 years of the study. However, cover of forbs was lower in treatment plots, and by the third year of the study, forbs were significantly (P<0.05) lower on plots without common mullein. The presence of common mullein may have altered natural competitive interactions between grasses and forbs in this area [7]. Juvik and Juvik (as cited in [31]) suggest that grazing by feral sheep and goats in areas of Hawaii may have facilitated the establishment, spread, and persistence of common mullein in niches once occupied by the endangered Hawaii silversword (Argyroxiphium sandwicense subsp. sandwicense). Feral sheep and goats likely avoided common mullein in favor of other more palatable forage [31].

Control: Minimizing disturbances may be the most effective and economical method of common mullein control. Limiting open sites restricts common mullein's success. However, the very long-lived seed bank suggests that eradication of common mullein is unlikely, and even minimal disturbances may encourage common mullein establishment. In many areas, common mullein populations do not persist and abundance is dramatically reduced as time since disturbance increases. Potential control methods are discussed below.

Prevention: As a biennial species with a persistent seed bank, common mullein is adapted for widespread dispersal through time. The sudden appearance of common mullein is likely after disturbances expose buried seeds to light [13]. High levels of germination are possible in a wide range of temperatures, and germination percentages can be increased by 38% after only 5 seconds of light exposure [51].

Given the long-lived seed bank and wide range occupied by common mullein, transportion of soil may introduce or encourage common mullein establishment. Common mullein seedlings emerged from soil collected in a wetland constructed by a Department of Transportation mitigation project on New Jersey's Delaware River but did not emerge from soil taken from preexisting, nearby natural marshes [85].

Increased levels and frequencies of disturbances may increase the density of the common mullein seed bank. In northern Arizona, the density of common mullein seedlings emerging from soil samples increased with increased levels of past land use. There were 940 seedlings/mÂ² in high disturbance areas and 566 seedlings/mÂ² from areas with more moderate levels of disturbance [73].

Physical/mechanical: Physical control methods may be an effective method of removing small aboveground common mullein populations. Plants severed through the root crown below the basal leaves do not sprout [16]. Flowering stalks should be removed from the site to limit additions to the seed bank. In greenhouse experiments, common mullein did not survive defoliation in low-nitrogen environments [140].

Fire: See Fire Management Considerations.

Biological: There have been no purposeful introductions of common mullein biological control agents. In Europe, common mullein is most negatively affected by weevils (Gymnaetron tetrum) and mullein moths (Cucullia verbasci) [93]. Weevils were accidentally introduced in North America. Weevils can destroy all seeds within a capsule but rarely infest all capsules. Weevils may destroy up to 50% of common mullein seeds [16].

Chemical: Egler [42] reports that first year rosettes are easily killed by herbicide but that second year plants are more resistant. However, a review reports that common mullein's extreme hairiness reduces the effectiveness of herbicides. Aiming herbicides directly into the center of the rosette may increase herbicide effectiveness [16].

Integrated management: In the available literature, there was little mention of integrated management methods for common mullein. In a review by Reed [108], guidelines are provided for limiting the establishment and evaluating the potential impacts of nonnative and/or invasive species in restoration projects. Reed presents plans to limit and prepare for potential weedy species establishment as well as decision-making guidelines on whether to actively manage the weeds.

Habitat characteristics ¹¹

More info for the term: cover

Common mullein occupies open sites. It is often described on disturbed sites such as roadsides, shores, fields, clearings, and vacant lots throughout its range [30,78,104,143,147] but is possible in any habitat without dense cover [41].

Climate: Common mullein tolerates a wide variety of growing conditions. Wide ecological amplitude has likely been more important than adaptation to local conditions in establishment and spread of this species. When common mullein seed collected from different elevations (246-7,421 feet (75-2,262 m)) in California [102] and in Hawaii [7] was grown in a common garden, relationships between elevation and distinctive plant traits were rare. Researchers in California suggested that common mullein has a "general-purpose genotype" [102]. Results were similar when seedlings from seed collected in Texas, Colorado, and Alberta were grown in a common area. Seedlings had similar photosynthetic rates at temperatures from 68 to 95 Â°F (20-35 Â°C). Although photosynthetic rates were higher at the coldest temperatures for plants from seed collected in cool habitats, researchers indicated that wide-ranging tolerances and not rapid local adaptation was most important to common mullein's wide distribution and success [149].

Differences in climate, latitude, and associated vegetation may affect development and life history of common mullein populations from southern Canada, North Carolina, Texas, and Georgia. In southern Canada, the growing season is short and precipitation ample and reliable. In North Carolina and Georgia, precipitation is abundant, and the growing season is long. In Texas, the growing season can be cut short by drought conditions. Sites in southern Canada with sparse vegetation had the most common mullein plants that did not flower until 3 or 4 years old. Annual common mullein plants were most common in Georgia, where associated vegetation cover increased to nearly 100% in 2 growing seasons. The most rapid annual development occurred in populations from southwestern Texas, where annual precipitation was lowest and hard frosts were uncommon [109,110]. The largest common mullein plants occurred on Texas sites with favorable moisture [111]. Life history differences between common mullein populations from southern Canada to Texas and Georgia [110] Population location, number Probability of fruiting

Proportion fruiting as

annuals biennials triennials Southern Canada, n=10 0.52 0 0.92 0.13 North Carolina, n=6 0.64 0 0.93 0.05 Texas, n=6; Georgia, n=2 0.62 0.27 0.73 0.01

Elevation: In Hawaii, common mullein occupies sites from near sea level to 4,596 m (15,080 feet) [7]. Elevation tolerances are not as wide for the rest of the United States. Elevation range for common mullein in the western United States State Elevation (feet) Arizona 5,000-7,000 [67]
3,200-7,200 in Grand Canyon region [126] California less than 7,200 [58] Colorado 4,500-9,000 [56] Nevada 4,000-8,700 [66] New Mexico 6,000-8,500 [92] Utah 4,000-9,010 [147]

Soils: Soil type is probably not important in limiting common mullein establishment or successful reproduction. Common mullein is described on "light" soils in Nova Scotia [113], "heavy" soils in Wisconsin [32], coarse soils in the Great Plains [131], and well-drained soils in the Adirondack Uplands [75]. Reinartz, who studied common mullein populations from southern Canada to Georgia and Texas, indicated that common mullein "thrives" on dry, infertile, highly calcareous soils as long as sunlight is abundant [109].

Sources and Credits

(c) jacinta lluch valero, some rights reserved (CC BY-SA), https://www.flickr.com/photos/70626035@N00/16858296547/
(c) Steve Chilton, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/73779416@N00/898761454
(c) Seth Anderson, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/swanksalot/491222435/
(c) Sebastian Stabinger, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/IMG_6745_crop.JPG/460px-IMG_6745_crop.JPG
(c) Steven J. Baskauf, some rights reserved (CC BY), http://bioimages.vanderbilt.edu/baskauf/25689
(c) 2012 Barry Rice, some rights reserved (CC BY-NC-SA), http://calphotos.berkeley.edu/cgi/img_query?seq_num=419716&one=T
(c) 2012 Barry Rice, some rights reserved (CC BY-NC-SA), http://calphotos.berkeley.edu/cgi/img_query?seq_num=419719&one=T
Adapted by Kate Wagner from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Verbascum_thapsus
(c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22948890
Public Domain, http://eol.org/data_objects/24630481
Public Domain, http://eol.org/data_objects/24630472

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Great Mullein

Summary 8

Ecological threat in the united states 9

Impacts and control 10

Habitat characteristics 11