The Biology of Canadian weeds. 150 Erechtiteshieraciifolius (L.) Raf. ex DC.

Stephen J. Darbyshire1, Ardath Francis1, Antonio DiTommaso2, and David R. Clements3

1Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, 960 Carling Ave., Wm.Saunders Bldg. #49, Ottawa, Ontario, Canada K1A 0C6 (e-mail: stephen.darbyshire@agr.gc.ca); 2Department

of Crop and Soil Sciences, 903 Bradfield Hall, Cornell University, Ithaca, NY 14853, USA; and 3BiologyDepartment, Trinity Western University, 7600 Glover Road, Langley, British Columbia, Canada V2Y 1Y1.

Received 10 January 2012, accepted 3 March 2012.

Darbyshire, S. J., Francis, A., DiTommaso, A. and Clements, D. R. 2012. The Biology of Canadian weeds. 150 Erechtiteshieraciifolius (L.) Raf. ex DC. Can. J. Plant Sci. 92: 729�746. Erechtites hieraciifolius, American burnweed, is a herbaceousannual in the Asteraceae native to forest zones of eastern North America, but introduced to parts of Europe and thePacific region. Confusion sometimes arises in distinguishing it from other weedy rayless composites in Canada, such asSenecio vulgaris (common groundsel) and Conyza canadensis (Canada fleabane). A pioneer therophyte species of forestzones, it occurs in large numbers when associated with major disturbances such as forest fires, but is also common in areasof smaller scale disturbance such as shores, forest edges and wind-throws. Soil conditions may vary greatly in nutrientcontent, moisture content, pH and salinity. In Canada, it is generally considered a minor garden and agricultural weed. Itis most common in crops such as lowbush blueberry (Vaccinium spp.), cranberry (Vaccinium macrocarpon), strawberry(Fragaria�ananassa) and vegetable crops; however, it occasionally occurs in other field and forage crops. Impacts includea variety of problems contributing to increased production costs or crop yield losses, including herbicide resistance,resource competition, and as a reservoir harbouring crop pathogens. It has been valued as a medicinal herb for treatinga variety of ailments. Populations may grow rapidly in response to disturbances typical of managed landscapes, butE. hieraciifolius can usually be effectively controlled by chemical, cultural or manual weed control tactics.

Key words: Erechtites hieraciifolius, American burnweed, erechtite a feuilles d’eperviere, pilewort, weed ecology,weed biology

Darbyshire, S. J., Francis, A., DiTommaso, A. et Clements, D. R. 2012. La biologie des mauvaises herbes au Canada. 150

Erechtites hieraciifolius (L.) Raf. ex DC. Can. J. Plant Sci. 92: 729�746. L’erechtite a feuilles d’eperviere (Erechtiteshieraciifolius) est une herbacee annuelle de la famille des Asteracees indigene aux regions forestieres de l’est de l’Ameriquedu Nord, mais qui a ete introduite dans certaines parties de l’Europe et du Pacifique. On la confond parfois a d’autresadventices a rayons courts de la famille des Composees qui poussent au Canada tels le senecon vulgaire (Senecio vulgaris)et la vergette du Canada (Conyza canadensis). Espece pionniere therophyte, on en retrouve de grand peuplements auxendroits qui ont subi de profondes perturbations comme un feu de foret, cependant l’espece colonise souvent des zones plusrestreintes comme les rivages, la lisiere des boises et les chablis. Les conditions du sol peuvent varier considerablementquant a la concentration d’elements nutritifs, la teneur en eau, le pH et la salinite. Au Canada, on la consideregeneralement comme une adventice secondaire dans les jardins et les champs. L’erechtite a feuilles d’eperviere se rencontrele plus souvent dans les cultures comme le bleuet nain (Vaccinium spp.), la canneberge (Vaccinium macrocarpon), la fraise(Fragaria�ananassa) et les plantes maraıcheres, cependant, on la decouvre a l’occasion dans d’autres grandes cultures etdes cultures fourrageres. Elle engendre divers problemes qui concourent a accroıtre les couts de production ou a reduire lerendement, notamment la resistance aux herbicides, la concurrence pour les ressources existantes et le fait de servir dereservoir aux agents pathogenes des cultures. L’espece est prisee pour ses vertus medicinales et on s’en sert pour soignerdivers maux. Les peuplements prennent parfois rapidement de l’ampleur a la suite des perturbations typiques auamenagements paysagers, mais on peut habituellement venir a bout de E. hieraciifolius par les moyens de lutte chimique,culturaux ou manuel.

Mots cles: Erechtites hieraciifolius, erechtite a feuilles d’eperviere, American burnweed, pilewort, ecologie des adventices,biologie des mauvaises herbes

1. Name and Generic StatusErechtites hieraciifolius (L.) Raf. ex DC. * Synonyms(spelling not corrected): Senecio hieracifolius L.; E.hieracifolia var. intermedia Fern.; E. praealta Raf.; E.hieracifolia var. praealta (Raf.) Fern.; Eriophthalmia

hieracifolia (L.) Prov.; Neoceis hieracifolia (L.) Cass.Common names: American burnweed (Darbyshire et al.2000), eastern burnweed, fireweed (fire-weed), pilewort(Darbyshire 2003), butterweed (Belcher 1956), whitefireweed (Fogg 1945); erechtite a feuilles d’eperviere

Abbreviation: DALPT, days after late postemergence treatment

Can. J. Plant Sci. (2012) 92: 729�746 doi:10.4141/CJPS2012-003 729

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(Darbyshire et al. 2000), creve-a-yeux, creve-z-yeux(Darbyshire 2003). European and MediterraneanPlant Protection Organization (Bayer) code: EREHI.Asteraceae (Compositae): aster family � Asteracees(Composees).

The name has often been spelled as ‘‘E. hieracifo-lia’’or ‘‘E. hieraciifolia’’. According to the InternationalCode of Botanical Nomenclature (McNeill et al. 2006),Erechtites hieraciifolius is correct, the genus beingmasculine in gender and an ‘‘i’’ being required betweenthe two elements (‘‘hieraci’’ and ‘‘folius’’) of the epithet(i.e., a double ‘‘i’’). Augustin de Candolle (DC.) wasthe first to publish the name E. hieraciifolius in 1838,based on the earlier name and description, Seneciohieraciifolius, by C. Linnaeus (1753). In doing so deCandolle acknowledged that C. S. Rafinesque (Raf.)had suggested this to him in a letter; the nomenclaturalauthority may be given as ‘‘Raf. ex DC.’’ (as above) orsimply ‘‘DC.’’ (McNeill et al. 2006). For a morecomplete list of synonyms see Belcher (1956).

This account deals with E. hieraciifolius var. hieracii-folius, the only variety present in Canada, and not withthe nearly pantropical weed E. hieraciifolius var. caca-lioides (Fisch. ex Spreng.) Griseb. (see Section 2c), unlessexplicitly mentioned.

2. Description and Account of Variation(a) Description * The following description is ofE. hieraciifolius var. hieraciifolius, the variety presentin Canada and most of the United States. It showsconsiderable phenotypic variability (Belcher 1956),especially in plant size and leaf shape (Fig. 1). Thedescription here is based on material from Canadianpopulations, supplemented with information from pub-lished descriptions (e.g., Fernald 1917; Kummer 1951;

Belcher 1956; Gleason and Cronquist 1991; Barkley andCronquist 1978; Barkley 2006).

Annual herb, (5�) 50�200 (�300) cm tall; taprootwith fibrous secondary roots; stem erect, more or lessstrongly ribbed (grooved), simple or branched towardthe top, glabrous to villose with translucent multicellularhairs; leaves alternate, the lower (3�) 6�20 cm long�(1�) 2�8 cm wide and diminishing in size upwardly,mostly glabrous or margins ciliate with short hairs andlower surface usually also with longer multicellular hairs(especially along the principal veins), irregularly toothedand lobed, with secondary veins extending to themarginal gland-tipped teeth (Fig. 2); lower leaves ellipticto broadly lanceolate, shallowly toothed to weakly acutelobed, usually weakly petiolate; middle to upper leaveslanceolate, acute, irregularly toothed, often deeply acutelobed, sessile or clasping at the base, with distal leavesbract-like.

The leaves are highly variable in size and shape. Thebase may be attenuate to a distinct petiole (Fig. 1B;Lloyd and Lloyd 1887), broadly sessile, or expanded andclasping to auriculate (Fig. 1A). Several leaf forms areoften visible on the same plant and those with claspingor auriculate bases tend to be larger toward the middleof the stem.

Inflorescence varying from a single terminal capitu-lum (flower head) in depauperate specimens (Fig. 1C)to compound, corymbose panicles usually with manycapitula (often 100 or more) on robust plants; capitulasubcylindric or flask-shaped (slightly swollen at thebase), (6.5�) 10�17 mm long, with a few linearbracteoles at the base and upper pedicel (sometimescollectively referred to as a calyculus); phyllaries(involucral bracts) about 20 in a single row, linearwith a slender attenuated tip, (6�) 10�17 mm long and

Fig. 1. Erechtites hieraciifolius: A. Drawing from Hermann (1705) with leaves lobed and clasping to auriculate (note lower leaveswith attenuate bases); B. Drawing from Millspaugh (1887) showing upper stem with reduced dentate leaves and linear inflorescencebracts and bracteoles, a middle leaf with attenuate (more or less sessile) base; C. Diminutive mature plant with a single capitulum.

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0.5�1.5 mm wide, becoming strongly reflexed with age;ligulate (ray) florets lacking but florets heterogamous,the outer florets pistillate, 10�100�, corollas whitish toyellow, tubular filiform, 4�5 deltate lobes, erect; discflorets 10�20 (�50�), mostly bisexual and fertile,inner sometimes functionally staminate, corollas whit-ish to pale yellow or pinkish, 4�5 erect to spreadingdeltate lobes; receptacle naked, 5�8.5 mm diam.;cypselae (fruits) narrowly cylindric to oblong, 2�3 mmlong, brown with 8�12 paler ribs, strigose (rarelyglabrous) between the ribs, the apex with a conspicuouscollar and persistent style base protruding from the

centre (Fig. 3C); pappus of copious white hairs, about5�10 times as long as cypsela, becoming readilydetached (Fig. 3A, C); naked seeds (i.e., cypselawithout the ovary wall) mostly dark blue to blackishwith a whitish zone at the base, testa finely verrucose(Fig. 3D).

As is typical in the Asteraceae, the dispersal unit(diaspore) is a cypsela, defined as a type of fruit formedfrom a single-seeded inferior ovary (Fig. 3C). The seed,technically defined as a ripened ovule, is left only whenthe ovary wall is removed (Fig. 3D). Except in Section8C, where the distinction between fruit and seedbecomes important, the term ‘‘seed’’ will be used torefer to the entire fruit.

Cotyledons (Fig. 3B) round to oval, entire or faintlylobed or emarginate, 6�9 (�10)�(3.5�) 5�9 mm,usually red-tinged beneath, a few scattered bristly shorthairs above and on the usually purple principal veinsbeneath, and a granular bloom on the lower surface.

Chromosome counts on plants of E. hieraciifolius atOttawa, ON, were determined as n�20 by G. A.Mulligan in 1966 (collection number 3118; voucher�DAO 857169). This is consistent with published countsof n�20, 2n�40 (Cooper 1936; Ornduff et al. 1963;Coleman 1982).

(b) Distinguishing Features * In eastern Canada, Erech-tites hieraciifolius is distinguished from most othercomposites by its many flowered (20�150), relativelylarge (10�17 mm) capitula with the outer pistillate floretslacking ligules (rays), and the small (2�3 mm long)seeds with copious white pappus hairs. Superficially,

Fig. 2. Lower (abaxial) surface of leaf of Erechtites hieraciifo-lius showing secondary veins extending to the blade margins(somewhat obscure in the black and white version of thisphoto) and terminating in gland-tipped teeth. Translucent,multicellular hairs present along the veins (and margins). Insetshows a single hair.

Fig. 3. Erechtites hieraciifolius: A. Seed with pappus of copious hairs; B. Seedling at two leaf stage; C. Cypselae, showing brown,ribbed and pubescent wall of fruit; D. Seeds, showing bluish-black, finely verrucose testa.

DARBYSHIRE ET AL. * ERECHTITES HIERACIIFOLIUS (L.) RAF. EX DC. 731

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it somewhat resembles the annual Canada fleabane,Conyza canadensis (L.) Cronq., whose usually simplestalks reach comparable heights, and are topped bybranched inflorescences of numerous small capitula(about 3�4 mm long) with phyllaries of unequal lengthsand outer pistillate florets obscurely ligulate, and tinyseeds (1�1.5 mm long). The stems of Canada fleabaneare covered with simple hairs bent upward (adpressed),the leaves are crowded and numerous, linear andattenuated in shape; the leaf margins, when not entire,are often more coarsely toothed with small teeth lackingglandular tips.

The widespread species Senecio vulgaris L. (commongroundsel) is another annual species which usually lacksligulate florets. It may be distinguished from E. hier-aciifolius by: its deeply lobed mid-stem leaves (appearingcoarsely pinnatifid), with the lobes obtuse rather thanacute; the black tips of the calycular bracts (andsometimes also the phyllaries); smaller capitula about5�8 mm long; and, the smaller seeds, 1.5�2 (�2.5) mmlong. The annual rayless aster [Brachyactis ciliataLedeb.;�Symphyotrichum ciliatum (Ledeb.) G. L.Nesom] also has small capitula (5�11 mm long) andseeds (1.5�2.5 mm long), but there are multiple rows ofphyllaries and the leaves are linear to oblanceolate withentire and usually ciliate margins.

Several native species of Packera (�Senecio sensulato) in eastern Canada may also be confused with E.hieraciifolius, such as the rayless P. indecora (Greene)A. Love & D. Love, and the occasionally rayless P.paupercula (Michx.) A. Love & D. Love. These per-ennial species have smaller seeds (52 mm), lower leavesthat are distinctly spatulate with a long petiole (usuallyas long as or longer than the blade), and the mid-stemleaves somewhat lyrate.

(c) Intra-specific Variation * This species is highlypolymorphic throughout its range (Fernald 1917, 1950;Belcher 1956). Although several entities have beenvariously recognized taxonomically, as varieties ordistinct species, the variation is continuous within andbetween the forms (Deam 1940; Belcher 1956; Seymour1982). Most of the striking variation in plant size andleaf size and shape is attributable to phenotypicresponses to varying conditions (Belcher 1956). TwoNorth American varieties have been commonly recog-nized: var. hieraciifolius and var. megalocarpus (Fern.)Cronq. The latter is a form found only in coastal saltmarshes of New England (Barkley 2006), which differsfrom the typical form in its more succulent leaves andstems, a receptacle�8 mm in diameter, and larger seeds(4�5 mm) with 16�20 nerves (Barkley 2006). AlthoughFernald (1950) considered it a distinct species, otherauthors generally treat it as ‘‘merely a well-markedecotype of saline coastal marshes’’ with the morpholo-gical variation between the two forms being continuous(Cronquist 1946; Belcher 1956; Barkley 2006).

A third variety is present in the tropics, var. caca-lioides, and found in the West Indies and from Mexicothrough Central America to northern Argentina and insoutheast Asia and the East Indies (Belcher 1956). Thisvariety differs in its longer bracteoles which extend fromone-third to one-half the length of the involucre, and bythe presence of multicellular hairs on the bracteoles andphyllaries (Belcher 1956).

In addition to treating megalocarpus and cacalioidesas distinct species, Fernald (1917, 1950) recognized threeintraspecific taxa within E. hieraciifolius in easternNorth America [var. hieraciifolius (�var. typica), var.praealtus (Raf.) Fernald, and var. intermedius Fernald],based primarily on leaf size and shape. Few haveadopted this intraspecific treatment pointing out thatsingle populations may contain forms typical of all threevarieties (e.g., Deam 1940) and that leaf form and sizeare affected by the growing conditions (Fogg 1945;Belcher 1956).

(d) Illustrations * Various aspects of E. hieraciifoliusare illustrated in Figs. 1, 2, and 3. Variation in leaf shapeis shown in the different elements of Fig. 1. Cypselae,seeds and seedlings are illustrated in Fig. 3. Other usefulillustrations may be found in Pammel et al. (1913), Fogg(1945), Cronquist (1955), Muenscher (1955), Barkley(2006), Neal and Derr (2005), Jung and Chung (2010),Trewatha (2010), and USDA-NRCS (2011).

3. Economic importance(a) Detrimental * Various authors include it amongthe agricultural or forestry weeds in Canada (e.g.,Provancher 1862; Dalaire 1904; Clark and Fletcher1909; Groh and Frankton 1949; Wright 1950;Darbyshire 2003), although it is a pest of secondaryimportance. It is a relatively minor weed in cranberry(Vaccinium macrocarpon Aiton) and blueberry (Vacci-nium spp.) fields in Nova Scotia, Prince Edward Islandand New Brunswick where it is usually easily controlledwith broad-spectrum herbicides or sometimes handpulling (J. Calder, personal communication, NovaScotia Department of Agriculture, Truro, NS; G.Graham, personal communication, New BrunswickDepartment of Agriculture, Aquaculture and Fisheries,Fredericton, NB). Wild blueberry crops may be parti-cularly susceptible to infestations since periodic burningis often used as a tool for pruning and weed manage-ment (Penney et al. 2008). Data on labels of herbariumspecimens collected in Canada indicate that it sometimesoccurs in a wide variety of other crops, includingoat (Avena sativa L.), barley (Hordeum vulgare L.),maize (Zea mays L.), strawberry [Fragaria�ananassa(Weston) Duch. ex Rozier], onion (Allium cepa L.) andcarrot (Daucus carota L.), as well as fodder crops(Medicago sativa L.) and mixed pastures.

It is sometimes considered a weed in the easternUnited States (e.g., Pammel et al. 1913; Runnels and

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Schaffner 1931; Muenscher 1955). As in Canada, E.hieraciifolius is present in wild blueberry fields inMaine (D. Yarborough, personal communication, Uni-versity of Maine, Orono, ME) and cranberry fields inNew Jersey (Anonymous, undated), where, in highdensities, plants can obstruct harvesting equipment(D. Yarborough, personal communication, Universityof Maine, Orono, ME). As an adventive outside itsnative distribution E. hieraciifolius var. hieraciifolius, isa weed in the Pacific region (see Section 4) and centralEurope (Belcher 1956; Voss 1996). It has also become aserious agricultural weed in Hawaii, invading sugarcane (Saccharum officinarum L.) plantations in thatstate (Hanson 1962; Sund 1964). Haselwood andMotter (1966) stated that, in Hawaii, it was, ‘‘One ofthe most abundant weeds in moist cultivated areas;also a weed in pastures and rangelands.’’ AlthoughE. hieraciifolius is naturalised on all of the majorHawaiian islands (HEAR 2008), it is currently notas abundant as E. valerianifolius (Link ex Spreng.)DC. (F. and K. Starr, personal communication, USGeological Survey, HI).

It has been reported a weed in pine plantations in thesouthern United States (Britt et al. 1990; Gardiner et al.1991); as an increasingly important reservoir host forcrop pathogens including insects, fungi, nematodes andviruses (see Section 13a, b); as a weed of cultivated lands(Runnels and Schaffner 1931; Trewatha 2010); as a weedof pastures and forage grasses (Pammel et al. 1913;Muenscher 1955; Stephenson and Rechcigl 1991), andturf grass (Busey and Johnston 2006; Trewatha 2010).It is also reported as a problem weed in the containernursery industry (Neal and Derr 2005).

It is considered a potential weed in Australia where itis under quarantine (AQIS 2011). In Hungary it isconsidered an invasive pest (Csiszar 2006).

The presence of alkaloids (see also Section 7c) causeshepatotoxicity if the plants are consumed in sufficientquantity (Burrows and Tyrl 2001). The plant is fre-quently reported to have a noxious smell and taste, so itis unlikely that persons or livestock would voluntarilyconsume sufficient quantities to be at serious risk.However, the overall similarity between E. hieraciifoliusand some even more toxic Senecio species may causedifficulties through pest mis-identification and inap-propriate management decisions.

As implied by the French common name ‘‘creve-z-yeux’’, the pappus hairs were thought to pose a seriousthreat to the eyes (Provancher 1862). The flocculentpappus bristles may well cause eye irritation whenmanually threshing grain crops heavily contaminatedwith E. hieraciifolius, especially in relatively stagnant airspaces. The pappus bristles have scattered antrorsespicules which may contribute to the abrasion of softtissues such as eyes and lungs.

From a sociocultural perspective, Harper (1944)indicates that it is greatly offensive to aesthetic sensi-bilities, saying that, in Alabama, ‘‘Although harmless

enough, and never interfering with crops, this is one ofour most useless and disreputable-looking weeds, veryunattractive in appearance, and ill-scented besides.’’Vegetation management resources are not always ex-pended on an economic basis and such perceptions of‘‘weeds’’ can have a tremendous impact on our relation-ships with, and actions on, plants and landscapes.

(b) Beneficial * As a medicinal plant in North America,the use of E. hieraciifolius has had a complex andconfusing history which Lloyd and Lloyd (1887) reviewextensively. These authors indicate that ‘‘fireweed oil’’of North American commerce was usually derived fromother species (not E. hieraciifolius), but maintain that E.hieraciifolius oil has distinct benefits. Erichsen-Brown(1979) cited a number of early North American sourceson medicinal uses of the plant in treatment forhaemorrhage, wounds, skin diseases, dysentery, cholera,and as a purgative and emetic; as a source of a blue dyefor cotton and wool; and, its use by Algonquin nativepeoples to treat poison ivy [Toxicodendron radicans (L.)Kuntz] and poison sumac [T. vernix (L.) Kuntz]poisoning. Hale (1880) recommends its use in thetreatment of dysentery, menstrual disorders and gonor-rhoea. Millspaugh (1887) considered the plant’s volatileoil to be the principal active ingredient in a tinctureproduced from whole fresh flowering plants for use asan emetic and in treatment of such conditions as eczema,diarrhoea, haemorrhages and piles, but noted thatnausea and other adverse reactions could result fromuse of this tincture. In the early 20th century its use as amedicinal herb was sufficiently popular that collectorswere paid 2�3 cents per pound (Georgia 1914).

Many authors comment on the unpleasant or rankodour of the plant. In spite of this Fernald et al. (1958)suggest it could be used as a salad or potherb. Theplant’s odour does not seem to be consistently distaste-ful to all people.

In the Andes of South America the leaves and flowers(var. cacalioides) have been used in folk medicine as ablood depurative and the roots to treat cardiac disease(Lorenzo et al. 2001). The antioxidant and radicalscavenging properties of nine species of Asteraceaefrom Bolivia were investigated by Parejo et al. (2003);although some activity was exhibited by E. hieraciifolius,other species appeared more promising as sources ofcompounds for industrial and medical use.

In Japanese trials, E. hieraciifolius has been found tobe among the most efficient of the plants tested atassimilating atmospheric nitrogen dioxide (NO2) with asmuch as 10% of its total organic nitrogen contentderived from this source (Morikawa et al. 1998). Suchplants have the potential to act as important sinks foranthropogenic nitrogen oxides (Morikawa et al 1992;Morikawa 1996). Morikawa et al. (2003) proposed that‘‘green walls’’ using such nitrogen dioxide-philic plantscould be set up around buildings and on highway

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corridors to help sequester pollutants from car emissionsor other sources.

(c) Legislation * Erechtites hieraciifolius is not listed inany federal or provincial noxious weed legislation inCanada; and is similarly absent from federal and statelists in the United States. The state of New York haslisted E. hieraciifolius var. megalocarpus as endangeredin that state (USDA-NRCS 2011). Australia restrictsimportation of E. hieraciifolius where it is considered apotential threat and is regulated as a quarantine pest(AQIS 2011).

4. Geographic DistributionIn North America, Erechtites hieraciifolius var. hieracii-folius is found primarily in deciduous forest regions ofeastern Canada from the Maritime Provinces to westernOntario, and in the United States from New Englandwest to Minnesota in the north, and south to Floridaand eastern Texas. The distribution in Canada is shownin Fig. 4, based on 837 specimens in Canadian herbaria.References to its presence in Saskatchewan or Albertaare almost certainly erroneous (Boivin 1972; Harms2006), and probably based on the report by Hooker(1834). No specimen was seen to confirm literaturereports by various authors (e.g., Gleason and Cronquist1991) of occurrence in Newfoundland (Meades et al.2000; Barkley 2006). It has been reported as introducedto Washington State, apparently based on a singlecollection from Seattle (Cronquist 1955), and as spor-adically adventive on the West Coast (Barkley andCronquist 1978; Barkley 2006). It is not known to occurin British Columbia (Douglas et al. 1998; Barkley 2006).

Elsewhere in the world, E. hieraciifolius var. hieracii-folius is known from the West Indies (Belcher 1956) andhas been introduced to central Europe (Belcher 1956;Tutin 1976), Hawaii (Belcher 1956), Japan (Walker1976; Kamada and Nakagoshi 1990), China (Chienand Ku 1998), Taiwan (Wu et al. 2004; Jung and Chung2010), Korea (Shin and Braun 2000), and New Zealand(de Lange 1995).

5. Habitat(a) Climatic Requirements* Climatic conditions withinthe native distribution of E. hieraciifolius var. hieracii-folius vary from humid continental to maritime. Theplant extends over a wide latitudinal range in easternNorth America, from southern boreal (9498N) tosubtropical regions with considerable variation in aver-age temperature and day length hours. In Canada, it isnot known from areas with a growing season of lessthan about 160 d, or average precipitation of less thanabout 70 cm.

(b) Substratum * There is little information in theliterature on the edaphic requirements and tolerances of

E. hieraciifolius in Canada, but data on herbariumspecimen labels indicate the species will grow in a widerange of substrate conditions. Soil types reported arerather general, but include sand, clay, loam, rock, andgravel. It is found in moist to saturated soils of shores,flood plains, fresh and salt marshes, bogs, dune slacks,gravel bars and ditches, but also occurs in dry or well-drained substrates such as dry sands, talus slopes, andgranite balds. A wide range of substrate pH is toleratedas indicated by the collections from peat bogs tolimestone cliffs and talus. Although nutrient poor soilsare readily colonized, Wilson and Shure (1993) found E.hieraciifolius biomass production was greater at har-vested forest sites to which fertilizer was added.

More detailed analysis of soil types is found in someUnited States sources. The substratum in a pine forest inSouth Carolina, where E. hieraciifolius was among earlysuccessional species, consisted of a silty sand down to1.2 m underlain by a medium to fine clayey sand to 7.6m; and the upper soil layers averaged 87% sand, 6.4%silt and 6.3% clay-sized particles (Hunt and Shure1980). Following treatment of the soil with waste waterin the above area, soil organic matter decreased from 3.5to 1.5% and cation exchange capacity from an averageof 55 meq 100 g�1 in the top 5 cm to 28 meq 100 g�1 at10 cm and 10 meq 100 g�1 below 15 cm; but there wereotherwise no differences in the soil profile of treated anduntreated areas except for an increase in soil moisturefrom 8% in untreated areas to up to 15% in treatedareas (Hunt and Shure 1980). Forest top-soils in easternTennessee containing substantial seed banks of E.hieraciifolius were found to have 3.2�5.3% organicmatter, 4�11 mg g�1 phosphorus, 21�26% clay, 28�43% silt and 31�51% sand, with a pH of 5.2�6.0(Farmer et al. 1982). The predominant soil types ineastern mixed forest areas where E. hieraciifoliusappears following fires or forest clearance are loamsand silt loams originating from acid shales, sandstonesand limestones, often acidic with an average soil pH ofabout 4.5 (Coxe et al. 2006). In the wetland complex ofthe Delaware River (NJ), E. hieraciifolius was found inshrub forest habitats on alluvial and aeolian deposits(Leck et al. 1988).

(c) Communities in Which the Species Occurs * InCanada, E. hieraciifolius occurs in boreal (southernpart), Great Lakes/St. Laurence, Acadian and Caroli-nian forest regions (Fig. 4). The species usually occurs inabundance and high density in places of recent majordisturbance, although small scale disturbances givingrise to suitable microsites are colonized by smallnumbers of plants. Disturbances may result from fires(Masters et al. 1996; Nakagoshi et al. 2003; Hutchinsonet al. 2005), forest cutting (Boring et al. 1981; Masterset al. 1996; Landenberger and McGraw 2004; Mou et al.2005; Abella 2010), herbicide application (Kochenderferand Wendel 1983; Luken et al. 1994), cultivation

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(Fig. 5), flooding or hydrological changes (Shull 1914;Leck et al. 1988; herbarium specimen label data),erosion (Peterson et al. 1990), or other disturbances(Wagner 1966; Hunt and Shure 1980; Roman et al.1984). In hemlock [Tsuga canadensis (L.) Carriere]forests in New England damaged by an importedadelgid [Adelges tsugae (Annand)], it is among oppor-tunistic species said to have ‘‘invaded’’ the stands (Orwigand Foster 1998). It is a poor competitor (Boringet al. 1981) and Peterson et al. (1990) found that itwas negatively correlated (r��0.45, P�0.018) withtotal cover (primarily other plant species).

Population explosions may occur under these andother conditions where competition is reduced, butgenerally subside rapidly with successional progressionto less open environments. Shores of lakes and rivers,habitats characterized by natural disturbance, arecommon locations for E. hieraciifolius as are sitesassociated with beaver activities causing cyclical flood-ing and drainage. It is found in a wide range ofanthropogenic habitats where vegetation is regularlydisturbed or maintained at early successional stages,such as roadsides, railway lines, ditches, energy corri-dors, quarries, tree plantations, cultivated land, turf,flower beds, or ruderal sites. It grows in coniferous,deciduous or mixed forests, although usually in placesreceiving some direct sunlight such as openings, edges,or along trails. A variety of wetland habitats are alsosuitable, including shores, wet thickets, wet forests, wetprairies, marshes, bogs and fens (Fernald 1950; Romanet al. 1984; Gleason and Cronquist 1991; Voss 1996;Murphy et al. 2009; herbarium specimen label data). A1975 collection of E. hieraciifolius in southern Ontariocame from a Spaghnum moss (Spaghnum sp.) mataround a lake which had previously been flooded andwas then invaded by ‘‘hundreds of these weeds’’ after

the water level subsided (herbarium specimen labeldata, OAC).

Smaller scale disturbances also provide micrositeswhere reduced competition within a broader commu-nity allows small populations of E. hieraciifolius toestablish; e.g., tree falls and wind-throws (Peterson andPickett 1990; Peterson et al. 1990; Peterson and Pickett1995).

6. HistoryAs a native plant of deciduous and mixed forest areas,E. hieraciifolius has presumably been present in thosehabitats since the re-vegetation of de-glaciated areas ofsouthern Canada after the end of the last Ice Age. In theearly 19th century, when clearing of the great easternforests of North America had begun in earnest, E.hieraciifolius had become known as ‘‘fire-weed’’ becauseof its abundant occurrence in areas of forest clearance,especially where fires had occurred (Pursh 1814; Eaton1824; Torrey 1843). William Barton (1818) said that itwas ‘‘one of the commonest weeds [around Philadel-phia], growing almost every where, even on roofs’’.

7. Growth and Development(a) Morphology* All annual plants are consideredtherophytes, and this life-form is highly developed inE. hieraciifolius. The species can rapidly respond totake advantage of favourable growth conditions, rapidlyproducing large individuals in dense populations(Fig. 5). The phenotypic plasticity of its growth alsopromotes maximum reproductive effort under sub-optimal conditions. Depending on the availability ofmoisture, nutrients and light, plants may reach maturityat heights from a few centimetres and bearing only asingle capitulum, to more than 2 m with a few hundredcapitula (Fogg 1945; Csiszar 2006; Fig. 1). The plant iscapable of considerable morphological plasticity (see

Fig. 4. Map of distribution of Erechtites hieraciifolius in Canada, based on 837 herbarium specimens from ACAD (35), CAN (72),DAO (120), HAM (27), LKHD (2), MT (146), MTMG (37), NSAC (7), OAC (24), QFA (142), QK (27), QUE (61), TRT (75),TRTE (29), UNB (10), WAT (16), and WLU (7). Herbarium abbreviations follow Holmgren et al. (1990).

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Section 2) allowing a wide range of growth responses toenvironmental conditions.

(b) Perennation * A typical therophyte, E. hieraciifoliusis a ‘‘summer’’ annual over-wintering only as seeds. Ithas been postulated that some plants may behave aswinter annuals in southerly regions where winters aremilder than in Canada. In Kentucky, Baskin and Baskin(1996) found that 1% of freshly collected seeds germi-nated immediately in an unheated greenhouse. They alsoobserved some plants of such a large size that it seemedunlikely their growth could have been attained fromspring germinating seeds.

(c) Physiology and Biochemistry * The alkaloid hier-acifoline, reported from E. hieraciifolius by Manske

(1944), was later shown to be a mixture of twocompounds, senecionine and seneciphylline (Adamsand Gianturco 1956). Bohlmann and Abraham (1980)found a syringyl alcohol derivative and sesquiterpenes inthe roots of E. hieraciifolius.

In the re-growth following a forest clear-cut in NorthCarolina, E. hieraciifolius was found to contain 2.6990.05, 0.2590.01, 6.9790.75, 0.9890.05, and 0.3790.03percent dry mass, N, P, K, Ca, and Mg, respectively(Boring et al. 1981). The N, P, and K values were thehighest detected among all herbaceous species and mostwoody species (significantly higher values of N weredetected only in the sprouts of two tree species).

An analysis of oil extracted from aerial parts of E.hieraciifolius in Brazil found that 11 compounds con-stituted 94% of the oil, a-phellandarene (41.3%) andr-cymene (22.2%) being the main components (Lemoset al. 1998). Somewhat different results were obtainedfrom an analysis of fresh leaves and stems of plants fromBolivia (Lorenzo et al. 2001). In the latter analysis,22 components were identified as composing 93.3% ofthe oil, of which a-pinene was the main component(48%), followed by myrcene and (E)-b-ocimene (14%each), but only traces of a-phellandrene and r-cymenewere found.

Nutrients leached from mature leaves of E. hieracii-folius subjected to simulated rain were at rates of: 0.03mg 0.1 m�2 h�1 NH�

4 (ammonium ion); 2.4 K; 1.68Ca; 0.31 Mg; 0.26 NO�

3 (nitrate ion); and �0.93 P(Haines et al. 1985a). No significant difference in therate of nutrient leaching was detected at differenttreatment pH levels (2.5�5.5). Phosphorus was appar-ently absorbed from the simulated rain water ratherthan leached. The relatively high rate of nutrientleaching from the leaves was attributed to the wett-ability of adaxial leaf surfaces (Haines et al. 1985b) (seeSection 11). Tissue necrosis resulted from exposure topH levels below 2.5 (Haines et al. 1980).

The complex nitrogen metabolism has been exten-sively studied by Japanese researchers. Of the 217 plantspecies studied in laboratory experiments, Morikawaet al. (1998) observed that E. hieraciifolius had one of thehighest NO2 assimilation rates at 5.7 mg g�1 dry weight,representing 10% of the total nitrogen content. Averagelevels of nitrate (NO�

3 ); nitrite (NO�2 ) and ammonium

(NH�4 ) ions detected in the leaves of seedlings of E.

hieraciifolius by capillary electrophoresis were 16.8mmol, 8.2 nmol and 1.0 mmol per gram of fresh tissue,respectively (Kawamura et al. 1996). Of the six plantspecies studied by Kawamura et al. (1996), E. hieracii-folius contained the smallest quantity (in relation to wetweight) of NH4

�, and the largest quantity (in relation tochlorophyll content) of NO�

2 : The ability of E. hier-aciifolius to convert NO�

3 to nitrous oxide (N2O) wasdemonstrated by Hakata et al. (2003), although it wasone of the least efficient of the 17 species studied. Thecapacity of various plant species to convert NO�

3 toN2O (i.e., N2O emission) appears to be inversely

Fig. 5. A dense population of Erechtites hieraciifolius in NewJersey, 21 August 2008, Mr. Peter Craig in photo. The 1.6-hafield was treated with two applications of glyphosate (about a1-month interval), and then no-till planted with a variety ofnative grassland species. It is unknown whether the growth ofE. hieraciifolius was the result of a soil seed bank, seed rainfrom an outside source, or contamination of the planted seed.

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proportional to their ability to assimilate NO2 (Hakataet al. 2003).

(d) Phenology * Seeds mostly germinate in the spring(see Section 8c) and somewhat later with increasinglatitude. Flowering may begin as early as late July,but seed maturation occurs mostly through mid-Augustto early October (herbarium specimen label data).Robertson (1928) reported the flowering period inIllinois as Aug. 20 to Sep. 25. The basal leaves oftenbegin to wither as flowering commences (Barkley 2006).

(e) Mycorrhiza * The roots of E. hieraciifolius plantsgerminated from forest topsoils (from eastern Tennes-see) were extensively colonized by endomycorrhizaewith hyphae and vesicles present in all samples (Farmeret al. 1982).

8. Reproduction(a) Floral Biology * The capitula of E. hieraciifoliuslack ligulate florets to attract pollinators and areprobably primarily autogamous. Thirteen species ofmostly hymenopteran insect visitors were reported byRobertson (1928) in Illinois; however, they are unlikelyto be effective pollinators.

The cytology, histology and ontogeny of micro- andmegasporogenesis, and early embryo development in E.hieraciifolius were studied by Cooper (1936). Wagner(1966) studied the effects of radiation on embryoabortion rates (100% atB1.5 Gy d�1) in a field studyin Brookhaven, NY.

(b) Seed Production and Dispersal * The pappus ofcopious large hairs at the apex of the seed (Fig. 3A)facilitates wind dispersal (Fogg 1945; Ohtsuka 1998).Large plants are capable of producing thousands ofseeds (see Section 2). In Hungary, Csiszar (2006) foundthat an average of 32 390 seeds were produced per plant,although growing conditions were not indicated. In aforest area of NY, Wagner (1965) measured the seedrain of E. hieraciifolius from late summer to earlyautumn at 36 145 seeds ha�1.

In agricultural settings, E. hieraciifolius may also bedispersed through mechanical harvesting equipment(J. Calder, personal communication, Nova Scotia De-partment of Agriculture, Truro, NS; D. Yarborough,personal communication, University of Maine, Orono,ME).

(c) Seed Banks, Seed Viability and Germination * Theresults of various observations and experiments on seedbank formation of E. hieraciifolius are incongruous anddifficult to interpret. Germination tests of exhumedseeds, artificially buried for long periods, have shown

either no viability (Telewski and Zeevaart 2002) or asmuch as 89% germination after 8 yr (Baskin and Baskin1996). Some studies on germinating or recovering buriedseeds from forest soils have found few seeds (Oostingand Humphreys 1940; Livingston and Allesio 1968;Leck et al. 1988; Matlack and Good 1990; Schiffmanand Johnson 1992), in spite of the potential forimmigration of wind-borne seeds. The low numbers ofseeds and distributional patchiness in mature forest soilsfound by these studies suggests that long-term seedbanks are not formed. However, other studies havedetected large numbers of buried E. hieraciifolius seedsgerminating from forest soils (Farmer et al. 1982; Mouet al. 2005; Schelling and McCarthy 2007). Differencesin the results of studies measuring germination may bedue in part to experimental conditions and the cyclicalconditional dormancy exhibited by E. hieraciifolius(Baskin and Baskin 1996). Direct observation of ‘‘seeds’’in soil samples may be obfuscated by the rapid disin-tegration of the brown, ribbed fruit wall of the cypselawhich reveals a finely verrucose, dark blue to blackishtesta (Baskin and Baskin 1996; Fig. 3D). Although stillviable, the naked seeds (ripened ovules) are verydifferent in appearance and can be easily overlookedor mis-identified.

Few studies have been conducted in Canada. Theplant did not germinate from any of the soil samplesfrom mature deciduous forests at Mont St. Hilaire, QC(Leckie et al. 2000), although herbarium specimens havebeen collected indicating its presence throughout thearea (herbarium specimen label data).

Profuse germination of E. hieraciifolius is often notedin conjunction with water draw-downs, such as drainedbeaver ponds, emergent shorelines and flood plains(herbarium specimen label data). At Cold SpringHarbor, NY, abundant germination of E. hieraciifolius,along with more than 140 other species of plants, wasnoted on the bed of a recently drained millpond (Shull1914). Shull (1914) tried to artificially recreate similarconditions in the laboratory, but did not observe anygermination of E. hieraciifolius. In a Connecticut saltmarsh, Roman et al. (1984) found that E. hieraciifoliusgerminated well in areas where the soil water salinitywas near 0.5% throughout the growing season.

In North Carolina, Oosting and Humphreys (1940)examined seed germination from soil samples along aplant succession transect from cultivated fields toclimax oak-hickory forest; 10 sites were considered torepresent more than 200 yr of forest growth. No seedsof E. hieraciifolius germinated from soil collected atsites representing pre-afforestation communities, andonly small numbers of seedlings were detected atforested sites. Although no data are given on theabove-ground presence of E. hieraciifolius in any ofthe vegetation age classes, Oosting and Humphreys(1940) state that it is improbable that seeds immigratingfrom elsewhere would be able to readily penetrate litterlayers into the soil layers sampled. Livingston and

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Allessio (1968) reported similar results along a succes-sional transect in Massachusetts from abandoned fields,through conifer plantations, to mixed woodland; only4 seedlings were germinated from a total of 16 soilsamples, one each from 4 mid- to late-successionsamples. In a southern Appalachian mature oak forest(Montgomery Co., Virginia) with a low level of pastdisturbance, E. hieraciifolius was among pioneer speciesthat were either absent or present at very low densities(50.03 m�2) in the seed bank (Schiffman and Johnson1992). At sites where seeds were found in the soil (bygermination testing, but undetected in visual inspec-tions), adult plants were also found in the forestcommunity; however, no germination of E. hieraciifo-lius was observed in soil samples from sites whichlacked adult plants (suggesting limited immigration). Atdisturbed and undisturbed mixed oak forest sites in thecentral Appalachians (southeastern Ohio), Schellingand McCarthy (2007) germinated seeds of E. hieracii-folius from 79% of their soil samples, where it occurredmost frequently among the 70 species detected in theseed bank. Adult plants were also found in the above-ground vegetation in the study area. A study of severalforest soil seed banks in eastern Tennessee (Farmeret al. 1982) found that E. hieraciifolius was one of fivespecies germinating from 100% of the samples andtrials, that it produced the second highest number ofseedlings (mean of 127 425 ha�1) of the 95 speciesdetected, and, after 5�6 mo of growth, representedabout 32�42% (depending on substrate trial) of thetotal biomass of all germinated plants. Germinationtests on litter and soil (to 5 cm depth) from a pine(Pinus elliottii Englem.) plantation in South Carolina,found seedling densities of 26 m�2 (Mou et al. 2005),with almost all seedlings germinating from unscarifiedsoil samples.

The unsuitability of shade conditions in matureclosed-canopy forests, the scarcity of seeds in the litterand soil, and the rapid germination of E. hieraciifoliusfollowing cool burns and litter removal might suggestthat some seeds will remain dormant in the substratumuntil surface conditions permit access to sunlight(Glasgow and Matlack 2007), but might also suggestimmigration of wind-borne seeds from neighbouringopen areas (Matlack and Good 1990). For example, astudy of buried seeds after clear-cutting of an ancientstand of Pinus strobus L. in Connecticut found that E.hieraciifolius was not among plants germinated fromburied seeds, and that its substantial presence in theclearing arose from wind-dispersal of its seeds fromopen areas (Del Tredici 1977). Ecologists have cometo similar conclusions in Japan, where its explosiveoccurrence as an early pioneer of post-disturbanceforest succession is attributed primarily to anemo-chory (wind dispersal) rather than seed banking(Ohtsuka 1998).

Most studies of soil seed communities have beenconducted at upland sites. In a variety of wetland (bog)

communities in West Virginia, E. hieraciifolius seedsgerminated at rates of 0�55 seeds m�2 (McGraw 1987).Unfortunately data were not presented on the verticaldistribution (and therefore relative age) of germinatingseeds. At an upland site in West Virginia, Landenbergerand McGraw (2004) studied seed banks at two forestsites which had been clear-cut 7 yr previously. Theyfound E. hieraciifolius to be among the most abundantseeds (relative to other species detected) in the soil in theopen clear-cut and that seed densities declined inproportion to other species and logarithmically indensity across boundary between clear-cut and undis-turbed forest.

Baskin and Baskin (1996) found that in Kentuckyabout half of the freshly collected seeds were dormantand the remainder only germinated under warmerconditions. Unburied seeds which were winter-stratifiedgerminated the following spring, while buried seeds (alsostratified), germinated the April following exhumation.Buried seeds re-entered conditional dormancy eachOctober, but 89% of seeds remained viable after 8 yrof burial. Maximum germination occurred under ther-moperiods of 30:15 and 35:208C (12:12 h) and aphotoperiod of 14 h light:10 h dark, although consider-able germination also occurred in total darkness. InMassachusetts, Lincoln (1983) found that 85% offreshly harvested seed germinated in either light ofdark conditions at 20�308C within 14 d following a60-d cold treatment.

Although the vegetative community at the site of soilprovenance is not given, E. hieraciifolius germinatedfrom most of the 96 pots using soil from Ona, Florida,in a greenhouse study (Stephenson and Rechcigl 1991).It is not known whether germination was, in whole or inpart, from fresh (previous season) or dormant (seed-banked) seed, or whether seeds were from locally grownplants or transported from elsewhere. Germination ofseed tended to increase with soil pH (4.5�5.7) whenaugmented with dolomite, reaching a maximum at pH5.7 and then diminishing somewhat at pH 6.1�6.8achieved with gypsum addition. Also, plants growingat low soil pH (B5.2) were smaller and less vigorous.

(d) Vegetative Reproduction * Erechtites hieraciifoliusreproduces only by seed (Muenscher 1955).

9. HybridsNo inter-specific hybrids have been reported.

10. Population DynamicsThe rapidity with which large numbers of plants of E.hieraciifolius appear immediately after major distur-bance, then quickly begin to decline over the following2 or 3 yr, represents a classic example of an early pioneerspecies in the ecological succession of plants. Pursh(1814) noted the tendency of this plant to rapidly formextensive monocultures in recently cleared forest areas,

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particularly where the woody debris was burned in situ.Farmer et al. (1982) observed densities of 49�220�103

plants ha�1 when testing for seed germination fromsouthern Appalachian forest soils. When they measuredthe above-ground biomass 5�6 mo after germination(representing plant growth in the first season post-disturbance), E. hieraciifolius comprised 32�42% of thetotal plant biomass, more than twice as much asproduced any of the other 94 species under any of thesoil condition treatments. In the first year of re-colonization after total vegetation removal by herbicidein a West Virginia forest, E. hieraciifolius comprised22% of the ground cover (Kochenderfer and Wendel1983). In the second year it had fallen to 2% cover andwas not detected in subsequent years. In a NorthCarolina clear-cut forest, Boring et al. (1981) foundthat E. hieraciifolius biomass production was 59 kg ha�1

during the season following cutting (i.e., removal of allmarketable timber), which represented 13.6% of herbac-eous plant biomass and 3.4% of the total biomassproduction by all woody and non-woody plants. It wasthe only species making a substantial contribution to there-growth biomass which was not detected in pre-cutvegetation surveys. At a nearby study site, Elliott et al.(1998) reported that, in the first year of revegetationafter a severe disturbance, E. hieraciifolius biomassproduction was 1820 kg ha�1 and represented 37.1%of the biomass of the ground flora. A subsequent survey15 yr later did not detect any E. hieraciifolius, but after28 yr it was detected as a minor component (0.9 kgha�1, 0.2%). The occurrence of E. hieraciifolius in themore mature forest stage may be due to the creation ofsuitable microsites by local disturbances (Peterson et al.1990; Peterson and Pickett 1990).

At a woodland site in South Carolina, highly dis-turbed because of the regular spray disposal of waste-water, E. hieraciifolius growth was correlated to theamount of disturbance (Hunt and Shure 1980). In thehigh disturbance zone it reached a peak biomassof about 125 g m�2 in June, whereas in the lowerdisturbance zone a peak of about 50 g m�2 occurred inAugust. As an important component of the plantcommunity and insect host, the growth of E. hieraciifo-lius had a significant effect on the temporal patterns andproductivity of arthropod herbivores (see Section13aiii).

It is not clear whether the colonizing ability of E.hieraciifolius is primarily the result of seed dispersal andimmigration or long-term seed banking (see Section 8c).For example, seeds of E. hieraciifolius have been shownto be short-lived or transitory in mixed-oak hardwoodclearings in the southern Appalachians where they areabundant in the early-successional period, but rapidlydecline and are replaced by more shade-tolerant specieswith the growth of over-story trees and gradual canopyclosure in the late-successional period (Elliott et al.1997). In managed pine plantations in Ohio, theimportance value (sum of relative cover and relative

frequency) of E. hieraciifolius was 0.6 in un-thinnedcontrol plots and 9.5 in plots 3 yr after thinning (Abella2010). In a managed pine plantation in South Carolina,Mou et al. (2005), found the high importance value of E.hieraciifolius (6.3) attained in the first post-harvestgrowing season declined rapidly in the following 4 yr(3.8, 0.5, 0, and 0.2, respectively).

11. Response to Herbicides and Other ChemicalsThe leaf adaxial epidermis in E. hieraciifolius is essen-tially glabrous, lacks epicuticular wax, has a low waterdrop contact angle (about 708), and has a high water-holding capacity (Haines et al. 1985b). This wettabilityof the leaf surface promotes retention and penetration,and therefore effectiveness, of spray-applied foliarherbicides.

Little work has been done in Canada to assess theresponse of E. hieraciifolius to herbicides. A single postapplication of mesotrione at 101 g a.i. ha�1 early in theseason has provided good control of E. hieraciifolius inNew Brunswick cranberry fields (G. Graham, personalcommunication, New Brunswick Department of Agri-culture, Aquaculture and Fisheries, Fredericton, NB).Mesotione also controls E. hieraciifolius well in wildblueberry fields in Maine (D. Yarborough, personalcommunication, University of Maine, Orono, ME),although application rates are usually higher than inCanada.

The species was among the first plants for whichherbicide tolerance was reported. After less than 10 yr ofheavy use of 2,4-D in sugar cane fields of Hawaii,populations of E. hieraciifolius were showing reducedresponse to the ‘‘new’’ chemical control (Hanson 1956,1962).

Sulfometuron/hexazinone applied in granular formwas effective in early season control in pine plantations(Pinus taeda L.) in the southeastern US (Gardiner et al.1991). Sixty days after a late postemergence granuleapplication of sulfometuron�hexazinone at two rates(140.1 g a.i. ha�1�700.5 g a.i. ha�1 and 168.1 g a.i.ha�1�840.6 g a.i. ha�1, respectively) 94% control ofthe two major herbaceous weed species [E. hieraciifoliusand Eupatorium capillifolium (Lam.) Small] was ob-tained at a pine plantation site in Arkansas. By 120 daysafter a late postemergence, control from the twoapplication rates decreased to 70 and 80%, respectively.

Several broad-spectrum specialty herbicides havebeen registered in the United States which are claimedto control E. hieraciifolius in turf or other ornamentalplantings. A mixture of clopyralid and triclopyr at arecommended rate of 38 g a.e. ha�1 and 51 g a.e. ha�1,respectively, is registered for postemergence control inturf (Dow AgroSciences 2008). A mixture of dimethe-namid-P and pendimethalin at a recommended rate of1.7 kg a.i. ha�1 and 2.2 kg a.i. ha�1, respectively, isregistered for preemergence control in ornamentalplantings (BASF 2011). A mixture of dicamba, thien-carbazone-methyl and iodosulfuron-methyl-sodium at a

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recommended rate of 78 g a.i. ha�1, 4.9 g a.i. ha�1, and22.5 g a.i. ha�1, respectively, is registered for postemer-gence control in warm-season grass turf (BAYERUndated). A mixture of soil-applied trifluralin andisoxaben at a recommended rate of 3.4 kg a.i. ha�1

and 0.9 kg a.i. ha�1, respectively, is registered forpreemergence control in turf, nursery and ornamentalplantings (Dow AgroSciences 2010).

For container-grown nursery crops, Neal and Derr(2005) provide a table on the efficacy of a number ofpreemergence herbicides registered for use in ornamen-tal plantings in the US. Of the 11 herbicides tested, theyrate 4 as providing ‘‘good’’ control of E. hieraciifolius:flumioxazin (420 g a.i. ha�1); oxyfluorfen�oxadiazon(2.2�1.1 kg a.i. ha�1); oxyfluorfen�oryzalin (2.2�1.1kg a.i. ha�1); and, oxyfluorfen�pendimethalin (2.2�1.1 kg a.i. ha�1).

12. Response to Other Human ManipulationPrior to the advent of chemical herbicides, Dalaire(1904) stated that control could be accomplished bycultivation, hoeing and hand pulling. Even now incranberry and blueberry fields of the Maritime pro-vinces control is often accomplished by hand pulling(G. Graham, personal communication, New BrunswickDepartment of Agriculture, Aquaculture and Fisheries,Fredericton, NB). Manual pulling and mowing, priorto seed production, has also been recommended forcontrol in the United States (Runnels and Schaffner1931; Muenscher 1955). Diligent sanitation of harvest-ing equipment appears to reduce spread in wild blue-berry fields in Maine (D. Yarborough, personalcommunication, University of Maine, Orono, ME).

13. Response to Herbivory, Disease and HigherPlant Parasites

(a) Herbivory(i)Mammals, including both domestic and wild animals *No reports have been found indicating whether thebitter leaves with their unpleasant odour are palatableto mammals.

(ii) Birds and other vertebrates * No information wasfound.

(iii) Insects * The Chinese ladybeetle, Leis conformisBoisd. (Coccinellidae: Coccinellini), imported intoFlorida to combat the green citrus aphid, Aphis spir-aecola Patch (Homoptera: Aphididae), has been foundfeeding on the blossoms of E. hieraciifolius; althoughentire blossoms including stamens and pistils were eaten,no larvae, pupae or eggs were observed (Watson andThompson 1933). In a young pine forest in SouthCarolina, increased biomass of E. hieraciifolius led tosubstantial increases in arthropod trophic guilds, such as

sap feeders and leaf strippers from 51 mg m�2 inuntreated areas to up to 252 mg m�2 in treated areas.Sharp declines in the herbivore biomass corresponded todieback of the E. hieraciifolius (and other herbaceousplants) and increases in detritivore populations exploit-ing nutrients available in the litter.

Larvae of Palthis asopialis (Guenee) are reported tofeed on E. hieraciifolius, and a variety of other plants(Robinson et al. 2010). This noctuid moth is known tooccur only in extreme southern Ontario (Troubridgeand Lafontaine 2004) and Quebec (J. D. Lafontaine,personal communication, Agriculture and Agri-FoodCanada, Ottawa, ON). Larvae of Tyria jacobaeae L.(Arctiidae), a biological control agent established inCanada against Senecio jacobaea L. (Harris et al. 1975),were reported to feed and mature on E. hieraciifolius inforced feeding trials (Bucher and Harris 1961). OutsideNorth America, several species of moths have beenreported to include E. hieraciifolius in their host range(Robinson et al. 2010), including Hypercompe icasiaCramer (Arctiidae), Platyptilia molopias Meyrick (Pter-ophoridae), and Platphalonidia subolivacea Walsingham(Tortricidae).

Evidence of leaf-mining insects is not uncommon onherbarium specimens of E. hieraciifolius from Canada.The microlepidoptera Phyllocnistis insignis Frey & Boll(Gracillariidae) has been reported on E. hieraciifolius inthe US (Robinson et al. 2010). Although larvaeproduce track mines in a variety of herbaceousAsteraceae and the species has been reported fromseveral border States, it is not yet known to occur inCanada. A lepidopteran miner on Erechtites wasreported from Kentucky under the name Phyllocnistiserechtitisella Chambers, but no description was pro-vided and the name cannot be used (Chambers 1878).Reports of the Gracillariid Phyllonorycter insignis(Walsingham) attacking Erechtites species are in error(J.-F. Landry, personal communication, Agricultureand Agri-Food Canada, Ottawa, ON).

In south Florida, E. hieraciifolius is among the manyspecies of Asteraceae suitable as hosts for the leaf minerfly Phytobia maculosa (Malloch) [�Nemorimyza macu-losa (Malloch)] (Agromyzidae), whose larvae formlarge blotch mines on the leaves (Stegmaier 1967). Inthe vicinity of vegetable crops in Florida, the highlypolyphagous serpentine leaf miners Liriomyza sativaeBlanchard and L. trifolii (Burgess) (Agromyzidae) arefound on E. hieraciifolius (Genung et al. 1978; Genung1981; Schuster et al. 1991). In Taiwan, E. hieraciifoliuswas found to be a preferred host of the leafminer L.trifolii (Chien and Ku 1998). Although none of theseleaf-mining flies occur in the field in Canada, the latter isa pest of greenhouse crops (Broadbent and Olthof 1995;Dempewolf 2004; Lonsdale 2011).

In Arkansas, E. hieraciifolius is host to the tarnishedplant bug, Lygus lineolaris P. Beauv. (Heteroptera:Miridae) (Young 1986). A gall midge, Neolasioptera sp.(Diptera: Cecidomyiidae), has been reported on E.

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hieraciifolius in Florida, causing irregular stem swel-lings 2�5 cm long; and, a flower-head gall produced byAsphondylia sp. (Cecidomyiidae) has been reported onErechtites sp. from an unspecified North Americanlocation (Gagne 1989). Infestation by the cosmopolitanaphid species Brachycaudus helichrysi (Kaltenbach)(Homoptera: Aphididae) was found on E. hieraciifoliusin two Florida counties in 1997 (Halbert et al. 2000).Blatchley (1912) reported that a carabid beetle[Anisodactylus terminatus (Say)] was often seen feedingon ripening seeds in Indiana. In Kagoshima City,Japan, E. hieraciifolius was one of three plants infestedby an Asian moth, Nyctemera adversata (Schaller)(Lepidoptera: Arctiidae), with 72�92% of the larvaematuring in 27.5 d (Murakami et al. 1999). In hosttesting of the Lepidopteran Secusio extensa (Butler) asa biological control agent in Hawaii, E. hieraciifoliuswas found to be a poor host, with less than 2% oflarvae completing development on the plant (Ramadanet al. 2010).

(iv) Nematodes and other invertebrates * Several speciesof root-knot nematodes have been reported on E.hieraciifolius, including Meloidogyne enterolobii Yang &Eisenback (�M. mayaguensis Rammah & Hirschamm),M. javanica (Treub) and M. incognita (Kofoid & White)in association with or proximity to agricultural crops(Carneiro et al. 2006; Rich et al. 2010). However, theseare tropical and subtropical species and only the latter ispresent in Canada as a pest in greenhouse productionsystems (Ebsary and Eveleigh 1983).

(b) Diseases(i) Fungi * There are few reports of fungi on E.hieraciifolius in Canada (Ginns 1986). The powderymildew, Sphaerotheca fuliginea (Schltdl.) Pollacci [�Podosphaera fuliginea (Schltdl.) U. Braun & S. Takam.],has been reported on E. hieraciifolius in Ontarioand Quebec (Parmelee 1977; DAOM specimens),and Cicinobolus cesatii de Bary (�Ampelomyces quis-qualis Ces. ex Schlecht.), a parasitic fungus of powderymildews, was reported by J. Dearness in 1895 onE. hieraciifolius collected in London, ON (Farr andRossman 2010).

A number of other phytopathogenic fungi have beenreported on E. hieraciifolius in the United States (Farrand Rossman 2010) including downy mildews, Bremialactucae Regel (PA), and Peronospora halstedii Farl.[� Plasmopara halstedii (Farl.) Berl. & de Toni] (MA,MD, NJ, TX and WI); leaf spot fungi Cercosporaerechtitis G. F. Atk. (AL, FL, TX), Phyllostictaerechtitis F. L. Stevens & P. A. Young (HI), Ramulariawisconsina H. C. Greene (WI), and Septoria erechtitisEllis & Everh. (AK, DE, TX and WI); powderymildews Erysiphe cichoracearum DC. [�Golovinomycescichoracearum (DC.) V.P. Heluta] (MD), E. polygoni

DC. [�E. betae (Vanha) Weltzien] (NY), Sphaerothecacastagnei Lev. (VT), S. humuli (DC.) Burrill [�Podo-sphaera macularis (Wallr.) U. Braun & S. Takam.](eastern states, IA, IL, MN and MT), and S. macularis(Wallr.) P. Magnus [�Podosphaera macularis (Wallr.)U. Braun & S. Takam.] (MT, OH); root-rot fungusPhymatotrichum omnivorum Duggar [� Phymatotri-chopsis omnivora (Duggar) Hennebert] (TX); the stem-rot fungi Sclerotinia sclerotiorum (Lib.) de Bary (FL)and Sclerotium rolfsii Sacc. [�Athelia rolfsii (Curzi) C.C. Tu & Kimbr.] (FL); and, the leaf gall Synchytriumerechtitis M. T. Cook (LA). In other parts of the worldRamularia wisconsina was recently reported on E.hieraciifolius in Korea (Shin and Braun 2000), Cercos-pora erechtitis in Venezuela, Septoria erechtitis fromCuba and the West Indies, and the leaf spot pathogenMycosphaerella erechtitidina Petr. & Cif. was reportedfrom Cuba, the Dominican Republic and the WestIndies (Farr and Rossman 2010).

In a study of mildews and rusts affecting theAsteraceae (Kenneth and Palti 1984), Erechtites spp.were hosts to species of the downy mildews Bremiaand Plasmopara, to the rust genus Puccinia, and tothe powdery mildews Erysiphe and Sphaerotheca. InHawaii, E. hieraciifolius was among a majority ofplants tested which did not inhibit growth of the soilfungus Phytophthora palmivora Butler (Powell and Ko1986).

(ii) Bacteria * In laboratory testing Pseudomonascichorii (Swingle) Stapp and P. viridiflava (Burkholder)Dowson were found to be pathogenic on E. hieraciifolius(Tsuchiya et al. 1982). Both these bacterium species havebroad host ranges which include many crop species.

(iii) Viruses * In Florida, E. hieraciifolius was identifiedas a host for the Bidens mottle potyvirus (BMV), whichwas also infecting nearby lettuce (Lactuca sativa L.) andendive (Cichorium endivia L.) crops (Purcifull and Zitter1973).

(c) Higher Plant Parasites * No information has beenfound.

ACKNOWLEDGEMENTSJ. Calder, G. Graham, J. D. Lafontaine, J.-F. Landry,F. and K. Starr, and D. Yarborough are thanked forkindly sharing information and expertise. Peter Craig, ofNew Jersey, kindly provided the photograph in Fig. 5.Useful comments on the manuscript were provided by J.Cayouette (Agriculture and Agri-Food Canada) andMihai Costea (Wilfred Laurier University). We thankthe curators and staff of the following herbaria whomade material in their care available for study: ACAD,CAN, DAO, HAM, LKHD, MT, MTMG, NSAC,

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OAC, QFA, QK, QUE, TRT, TRTE, UNB, WAT, andWLU [see Holmgren et al. (1990) for institutionalabbreviations].

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