The Biology of Canadian Weeds. 143. Apocynum cannabinum L.

Antonio DiTommaso1, David R. Clements2, Stephen J. Darbyshire3, and Joseph T. Dauer4

1Department of Crop and Soil Sciences, Cornell University, Ithaca, NY, USA 14853 (e-mail: [email protected]); 2Department of Biology, Trinity Western University, Langley, British Columbia, Canada V2Y 1Y1; 3Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Wm. Saunders Building #49, Ottawa, Ontario, Canada K1A 0C6; and 4Department of Crop and Soil Sciences, Oregon State University, Corvallis, OR, USA 97331. Received 28 May 2008, accepted 28 April 2009.

DiTommaso, A., Clements, D. R., Darbyshire, S. J. and Dauer, J. T. 2009. The Biology of Canadian Weeds. 143. Apocynum cannabinum L. Can. J. Plant Sci. 89: 977992. Hemp dogbane, Apocynum cannabinum (Apocynaceae), is a perennial herb with white to greenish flowers in terminal clusters that produces pencil-like pods 1220 cm long. A highly variable plant, A. cannabinum may be distinguished from spreading dogbane (Apocynum androsaemifolium) by its shorter corolla (26mm compared with 510 mm), erect greenish-white petals (compared with recurved or spreading pinkish petals), seeds more than 3 mm long (compared with seeds less than 3 mm), and more erect leaves (compared with spreading or drooping leaves), although frequent hybridization between the two species obscures the identity of some individuals. Hemp dogbane is native to the United States and southern Canada, but most abundant in the upper Mississippi River Valley and east to the Atlantic coast. It has been increasing in other areas, and becoming more of a problem where conservation tillage is adopted. It infests crops such as corn (Zea mays), soybeans (Glycine max), wheat (Triticum aestivum), sorghum (Sorghum bicolor) and forages, and may cause livestock poisoning due to cardiac glycosides within its milky sap (but livestock generally avoid it). Potential medicinal uses of these compounds have been investigated, and the roots are a source of fibre. Control of A. cannabinum with various herbicides is difficult due to a thick cuticle, and one solution may be to target susceptible stages, such as seedlings or early spring growth. Cultivation may also control A. cannabinum, but care must be taken not to promote the proliferation of the plant through regrowth from fragmented roots and rhizomes. Rotation with alfalfa also reduces populations of A. cannabinum.

Key words: Hemp dogbane, APCCA, Apocynum cannabinum, Apocynaceae, weed biology

DiTommaso, A., Clements, D. R., Darbyshire, S. J. et Dauer, J. T. 2009. La biologie des mauvaises herbes au Canada. 143. Apocynum cannabinum L. Can. J. Plant Sci. 89: 977992. L’apocyn chanvrin, Apocynum cannabinum (Apocynace´ es), est une herbace´ e vivace aux grappes terminales de fleurs blanches a` verdaˆ tres qui donnent des gousses en forme de crayon de 12 a` 20 cm de longueur. L’espe` ce connaıˆ t d’importantes variations. A. cannabinum se distingue du gobe-mouches (Apocynum androsaemifolium) par une corolle plus petite (2 a` 6 mm contre 5 a` 10 mm), des pe´ tales blanc verdaˆ tre dresse´ s (plutoˆ t que rosaˆ tres, recourbe´ soue´ tale´ s), des graines de plus de 3 mm de longueur (comparativement a` moins de 3 mm) et des feuilles plus droites (et non e´ tale´ es ou tombantes), bien que la fre´ quente hybridation entre les deux espe` ces rende l’identite´ de certains plants plus obscure. L’apocyn chanvrin est une plante indige` ne des E´ tats-Unis et du sud du Canada qui abonde surtout dans le haut de la valle´ e du Mississipi et a` l’est, jusqu’a` la coˆ te de l’Atlantique. L’espe` ce prolife` re ne´ anmoins dans d’autres re´ gions et s’ave` re plus proble´ matique aux endroits ou` l’on pratique la conservation du sol. Elle infeste les cultures tels le maı¨ s(Zea mays), le soja (Glycine max), le ble´ (Triticum aestivum), le sorgho (Sorghum bicolor)et les plantes fourrage` res, au risque d’intoxiquer le be´ tail en raison des glycosides cardiaques que renferme sa se` ve laiteuse (les animaux l’e´ vitent ge´ ne´ ralement). On s’est penche´ sur les vertus me´ dicinales potentielles de ces compose´ s ainsi que sur les racines de la plante en tant que source e´ ventuelle de fibres. Les herbicides viennent difficilement a` bout d’A. cannabinum a` cause de l’e´ paisse cuticule qui la prote` ge. Une solution serait de s’attaquer aux stades plus fragiles, comme les plantules ou la germination, au printemps. Le travail du sol pourrait aussi faciliter la lutte, mais il faut prendre soin de ne pas favoriser la prolife´ ration de la plante a` partir des fragments de racines et de rhizomes. L’assolement avec la luzerne diminue aussi la population d’A. cannabinum.

Mots cle´s: Apocyn chanvrin, APCCA, Apocynum cannabinum, Apocynace´ es, biologie des mauvaises herbes

1. Names Apocynum cannabinum L. Common names: Hemp dog- lechuguilla, Indian hemp dogbane, rheumatism weed, bane, apocyn chanvrin, bitter root, black hemp, blind and westernwall; chanvre sauvage (Crockett 1977; hemp, bowman root, Canadian hemp, choctaw root, Becker 1981; Darbyshire et al. 2000; Darbyshire 2003; clasping-leaved dogbane, dropsy root, honey bloom, USDA-NRCS 2004). European and Mediterranean 977 978 CANADIAN JOURNAL OF PLANT SCIENCE

Plant Protection Organization (Bayer) code: APCCA. reddish at the base. Branches usually arise in the upper Apocynaceae, dogbane family, Apocynace´ es. half with the lateral branches surpassing the central stem Apocynum is derived from Greek roots, with apo at flowering. Leaves opposite or rarely whorled or meaning ‘‘off’’ or ‘‘away from’’, and kunon meaning alternate, yellowish-green to dark green or sometimes ‘‘dog’’ (Dalby 2004). glaucous, erect or slightly spreading (leaves tend to be more spreading in prostrate forms), glabrous or sparsely 2. Description and Account of Variation pubescent beneath, oval to lanceolate, rounded to acute (a) Species Description * The following description is at the apex and usually abruptly mucronate (Fig. 2). The based on information taken from the literature (Fernald largest leaves arise near the middle of the stem, the size 1950; Gleason and Cronquist 1991; Voss 1996), supple- diminishes toward the top and bottom, (1) 412 (14) cm mented by observations made by the authors. Measure- long, 0.55.5 cm wide. Leaves acute to rounded or ments are given as the typical range with unusual cordate at the base (Fig. 2) and may be sessile or on extremes in parentheses. short petioles to about 1 cm long. Inflorescences A herbaceous perennial (Fig. 1) producing a milky compact paniculate cymes, usually terminal on branches latex sap. Plants tough and fibrous, usually glabrous but and only rarely axillary. Flowers hermaphroditic, may be variously pubescent on stems, leaves and 5-merous, (2) 2.54.5 (6) mm long, whitish to greenish- inflorescences. Root system extensive with long vertical white and cylindric to urceolate (urn-shaped) (Fig. 1C). and horizontal roots and short rhizomes. Stems usually Calyx lobes lanceolate, about half as long as to nearly erect or sometimes prostrate, (1) 310 (15) dm tall, often equal the corolla. Corolla lobes (petals) more or less lanceolate and acute to oblong-lanceolate and erect or slightly spreading. Pistil with two semi-inferior ovaries. Each flower produces two thin pods (follicles) (4) 820 (22) cm long straight or slightly sickle-shaped (Fig. 1D). Seeds 46 mm long, 0.75 mm wide, with a coma (tuft of white silky hairs) (1) 35.5 cm long (Fig. 1E, F). Cotyledons strap-like (Fig. 3), 411 mm long, about 1.5 mm wide. Some authors have reported a chromosome numbers of n8 (Schu¨ rhoff and Mu¨ ller 1937) and 2n16 (Van der Laan and Arends 1985) for A. cannabinum of unknown provenances; although these counts have been called into question. Counts of 2n22 have been reported by Breslavetz et al. (1934) from an unknown

Fig. 2. Variation in the shape of leaves from the middle of the Fig. 1. Apocynum cannabinum var. cannabinum. A. habit, scale stem in Apocynum cannabinum as drawn from herbarium bar10 cm; B. roots, scale bar10 cm; C. flower, scale bar specimens. Upper row with short petioles and rounded or 1 cm; D. follicles, scale bar10 cm; E. seed with coma, scale clasping base of the blade attributed to var. hypericifolium; bar5 cm; F. seeds, scale bar1 cm. Illustration by Regina lower row with longer petioles and tapering base of the blade O. Hughes, United States Department of Agriculture. attributed to var. cannabinum. Scale bar1 cm. DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 979

asclepioid features of pollinaria and anthoecial coronae (hoods and horns) in Asclepias.

(c) Intraspecific Variation * Highly variable in both shape (Fig. 2) and pubescence of the leaves (Gleason and Cronquist 1991), A. cannabinum is self-sterile (see Section 8a) with out-crossing promoting variability and hybridization (Ransom et al. 1998b). This variability is evident from the number of papers claiming plants are glabrous (Anonymous 1970; Hartman 1986; Bradley and Hagood 2001), tomentulose (Doll 1994) or both (Balbach 1965; Becker 1981; Gleason and Cronquist 1991). It is not known what proportion of this varia- bility is due to phenotypic plasticity versus genetic diversity. Within the hemp dogbane complex, various species, subspecies or varieties have been distinguished in different ways by different authors (cf., Woodson Fig. 3. Seedling of Apocynum cannabinum var. hypericifolium 1930; Fernald 1950; Boivin 1966; Gleason and with cotyledons and first true leaves. Scale bar5 mm. Cronquist 1991) with taxa recognized and ranked based primarily on growth habit, pubescence, leaf shape and petiole length. The bewildering array of intermedi- provenance, Lo¨ ve and Lo¨ ve (1982) from Manitoba, and ate forms between the described taxa provides little Hill (1989) from Virginia. Studies by Balbach (1965) on confidence in intraspecific classifications (e.g., Hartman a number of populations in the United States and 1986; Gleason and Cronquist 1991; Voss 1996). Fre- Canada found the diploid number of 22. Inconsistencies quently, two species are recognized within the complex, in reported numbers may also be due in part to the small A. cannabinum and A. sibiricum Jacq. (e.g., Darbyshire size (0.8-1.0 mm) of the chromosomes, which hinders et al. 2000), but here we prefer to recognize these two their preparation and counting (Balbach 1965). forms as varieties, A. cannabinum var. cannabinum, with leaves tapering to a distinct petiole (310 mm long), (b) Distinguishing Features * Because of frequent which is more common in southern and eastern popula- hybridization between species in the genus (see Section tions, and var. hypericifolium A. Gray (A. sibiricum), which usually has a short petiole ( 3 mm long) and is 9) and the extensive morphological variation in Apoc- B more common in northern and western regions of North ynum cannabinum, there is confusion about character- America. A semi-decumbent or prostrate type, istics that accurately differentiate this species from the A. cannabinum var. hypericifolium f. arenarium (F.C. closely related A. androsaemifolium L. (spreading dog- Gates) B. Boivin, has been recognized from shores of bane) and the extent to which species segregates should rivers and lakes in eastern Canada and the United States be recognized (see Section 2c and Key at the end of the (Schaffner 1910). Extreme mat-forming plants, with paper). The corolla of A. cannabinum differs from that small, glabrous and sessile or slightly clasping leaves, of A. androsaemifolium, being shorter [(2) 2.54.5 (6) have been collected along the St. John River in New mm versus (5) 5.58 (10) mm], having the 5 erect or Brunswick and other scattered localities. This growth slightly spreading petals (versus strongly spreading or form appears to be a phenotypic response to growing recurved) and being white to greenish-white and without conditions (Schaffner 1910). Distinct ecotypes identified any rosy hue or interior red markings. The leaves of from different geographic areas may be recognized by hemp dogbane are usually erect or slightly spreading growth or morphological characteristics, and ecotypes from the stem, while those of spreading dogbane are may be characterized by unique leaf shape (Ransom strongly spreading or drooping. Although highly vari- et al. 1998a), but these forms probably do not warrant able in shape, the leaves of hemp dogbane tend to be formal taxonomic distinction. elliptic to more or less lanceolate (Fig. 2), while those of Since the species commonly frequents disturbed spreading dogbane tend to be broadly elliptic to some- habitats, it is possible that the landscape alterations what ovate (egg-shaped). Another species often con- following European settlement have facilitated the fused with A. cannabinum is Asclepias syriaca L. spread and inter-mingling of forms that were previously (common milkweed), but the leaves of A. cannabinum separate and more or less distinct. Ransom et al. (1998b) are lighter green and more pointed than those of found that the genetic distance-based grouping of A. syriaca, both the follicles and seeds of A. cannabinum collections of this species were not highly correlated are narrower and more elongate than those of A. syriaca with the geographic location from which the plants (Doll 1994) and the flower structure of A. cannabinum is originated, or with differences in morphological very different, lacking the typical highly specialized characteristics. In Colorado, however, 11 populations of 980 CANADIAN JOURNAL OF PLANT SCIENCE

A. cannabinum exhibited low heterozygosity at 11 loci (Curran et al. 1997). Soybean (Glycine max L.) losses with few polymorphisms at these loci; none contained ranged from 30 to 38% in Nebraska (Schultz and more than two alleles (Johnson et al. 1998). This low Burnside 1979a; Furrer et al. 1983) with Webster et al. heterozygosity is unusual for an obligate outcrossing (2000a) reporting a loss of 75% in an Ohio study when species, but may be due to the limited range (i.e., one shoot density was 28 shoots m2. Sorghum [Sorghum state) from which the populations were sampled, relative bicolor (L.) Moench] losses were similar, ranging from to the much wider North America range of this species. 37% to as high as 45% in Nebraska (Schultz and Johnson et al. (1998) speculated that this low hetero- Burnside 1979a). In Ohio, Loux and Berry (1991) zygosity indicated a long history of inbreeding ranked A. cannabinum as the second most important or bottlenecking, but without random genetic drift. perennial broadleaf weed after Canada thistle [Cirsium Ransom et al. (1998b) found genetic variation among arvense (L.) Scop.] in corn and soybeans. However, in 16 populations from Michigan and Illinois was less than many cropping situations, the concern over A. cannabi- would be expected based on morphological differentia- num is more one of appearance than actual crop loss tion. Relatively short genetic distances observed (Robison and Jeffery 1972; Evetts and Burnside 1973). between A. cannabinum and other Apocynum species For example, studies in irrigated corn in Nebraska were seen to indicate some interbreeding among these found little effect on yield, whereas dryland corn and species (Ransom et al. 1998b). Outcrossing with closely sorghum in the same area experienced 15 and 30% yield related species could have provided some of the genetic losses due to this weed, respectively (Evetts and Burn- variability observed among A. cannabinum populations. side 1973). Schultz and Burnside (1979a) found that A. cannabinum consistently reduced corn and sorghum (d) Illustrations * The plant and its principal parts are populations in Nebraska, but that effects on biomass, illustrated in Fig. 1. Variation in leaf shape of A. seed weight and protein content were inconsistent. cannabinum is illustrated in Fig. 2. A seedling with Owing to its perennial nature and extensive root system, cotyledons is shown in Fig. 3. A photo of a flowering A. cannabinum often grows in isolated circular patches plant is seen in Fig. 4. Woodson (1930) provides within a crop field, which can be particularly detri- illustrations of leaf, root and stem anatomy, as well as mental to crop yields (Evetts and Burnside 1973; Triplett the general habit of various segregate taxa. 1985). Certain crops may be more susceptible to infestations: Schultz and Burnside (1979a) found A. cannabinum was most prevalent in oat (Avena sativa 3. Economic Importance L.) and soybean crops in Nebraska and least prevalent (a) Detrimental * Apocynum cannabinum infestations in alfalfa (Medicago sativa L.), pasture, and winter can result in significant crop losses, affect harvesting wheat (Triticum aestivum L.). efficiency and result in livestock poisoning. Crop losses As with many other perennial weeds, increases in the in corn (Zea mays L.) due to hemp dogbane ranged from abundance of A. cannabinum have been linked to 9% in irrigated systems in Nebraska (Schultz and increased use of reduced tillage systems (Triplett and Burnside 1979a) to 15% in non-irrigated systems in Lytle 1972; Triplett 1985; Loux and Berry 1991; Webster Nebraska (Evetts and Burnside 1973) and Pennsylvania and Cardina 1999). In a greenhouse study, Wyrill and Burnside (1976a) found the allelopathic effects of leachate from live A. cannabinum reduced sorghum growth by 33% over a 20-d growth period. Schultz and Burnside (1978h) found a consistently greater depression of yield when corn, soybeans or sorghum were grown with live versus dead A. cannabinum plants. Hafemann and Jones (1986), however, found no allelo- pathic effect on corn, soybeans or sunflowers in a greenhouse study. Other cropping system changes, such as a reduction in alfalfa as a component in rotations, have lead to increased infestation by A. cannabinum in Wisconsin (Doll 1995). Apocynum cannabinum is in full bloom during winter wheat harvest, which causes the milky sap to ‘‘coat combine parts and adhere dirt and chaff’’ (Doll 1994). The sap contains a cardiac glycoside similar to that found in Digitalis species (Genkina et al. 1974; Furrer et al. 1983), as well as various kinds of alkaloids, but is Fig. 4. Terminal flower clusters of Apocynum cannabinum; not tanniferous (Cronquist 1981). The sap is toxic flowers are small and bell-shaped, and range in colour from and 1530 g of green leaves can kill a horse or white to greenish-white. cow (Muenscher 1951), but animals find the plant DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 981 unpalatable and animal poisonings are rare (Fyles 1920; does apocynum.’’ Some North American natives would Furrer et al. 1983; Doll 1994; Dalby 2004). make a tea to treat heart palpitations and a variety of other medicinal purposes such as to treat colds, earaches, (b) Beneficial * The strong roots of A. cannabinum have headaches, nervousness, dizziness, or worms, or as an been used by North American natives as a source of emetic, antispasmodic, catharti, anodyne, hypnotic, or fibre for a number of applications such as bowstrings, laxative (Moerman 1998). Additionally, a shampoo can nets, rope, thread, and cloth (Woodson 1930; Hill 1952; be produced from crushed roots that would remove USDA-NRCS 2004). Each plant can yield up to 0.75 m dandruff and head lice. Poultices made from leaves were of fibre with a tensile strength of hundreds of kilograms used to treat various skin inflammations and eye diseases (Turner et al. 1980). In Idaho, Oregon and Washington, (USDA-NRCS 2004). Native Americans used the cordage for ritual basket making, ceremonial bags and cloth weaving, and in (c) Legislation * Apocynum cannabinum is not listed as California, the weed is still harvested for its fibre today a noxious weed on any Canadian federal or provincial (USDA-NRCS 2004). The fibres were an important weed legislation. It is listed as a noxious weed federally commodity to the native tribes of the Columbian in the United States due to its toxicity to livestock and Plateau, including the Nez Perce, Spokane, Umatilla invasive characteristics (USDA-NRCS 2004). and others for baskets and fishing nets (USDA-NRCS 2004) and the Chemeweve made snares for otter and 4. Geographical Distribution rabbits from the root fibres (Merriam 1955). The A native plant of North America, A. cannabinum is Luisen˜ o of southern California used it to construct their present in all Canadian provinces and territories except dance regalia, by incorporating golden eagle feathers Nunavut and the Yukon (Fig. 5); however, Cody (1996) into a netting of fibres (Merriam 1955). Another use of included it in his Flora of the Yukon Territory, great cultural significance for the Columbian peoples indicating that its presence in that region is to be was the creation of the itatamat or ‘‘counting the days’’ expected. In the United States, A. cannabinum is present ball, wherein a woman would record events in her life by in all 48 contiguous states (Anonymous 1970; Kartesz tying a knot in a length of cordage (USDA-NRCS 1999), although it is most common in the upper 2004). Mississippi River Valley and east to the Atlantic coast Apocynum cannabinum is effective in erosion control (Becker 1981). The abundance of this species has been and is attractive to bees and butterflies producing a fine increasing in other regions, such as the Missouri River grade of honey (Pellett 1976; Turner et al. 1980; Dalby area in Iowa, Nebraska and Kansas (Becker 1981). It 2004; USDA-NRCS 2004). Foster and Karpiscak (1983) has also been introduced to Germany (Radkowitsch listed A. cannabinum, along with milkweed (Asclepias 1999). spp.) and rabbit bush [Chrysothamnus nauseosus (Pursh) Britton], as a potential biofuel crop, particularly for 5. Habitat potential use in the Intermountain/Rocky Mountain (a) Climatic Requirements * Able to grow in numerous region of the United States where it can grow under arid habitats, A. cannabinum is highly variable and adaptable conditions. This species may also provide a source of (Balbach 1965). Optimal growing conditions include a latex for rubber production, with plant tissues contain- maximum annual precipitation of approximately 152 ing more than 5% latex (Woodson 1930; Hill 1952). A cm, and a minimum of 100 frost-free days (USDA- permanent brown to black dye was produced from the NRCS 2004). It has been found to grow at elevations up plant by decoction (i.e., extraction of plant material) to 5000 m in California (USDA-NRCS 2004). Evetts (Millspaugh 1887) and the dye is still used today and Burnside (1971) found that common milkweed (Anonymous 2009). (Asclepias syriaca L.) was less sensitive to moisture Because of its production of glycosides and alkaloids, stress than A. cannabinum. A. cannabinum has been investigated as a source of medical products (Zaitseva and Feofilaktov 1950; (b) Substratum * Information from the labels of Babcock and Carew 1962; Lee et al. 1972). Cymarin, a herbarium specimens collected in Canada indicates a major constituent of A. cannabinum, has been used in the wide variety of soil types including, sandy soil, dry soil, treatment of congestive heart failure (Burger 1960; alluvial gravel, rocky soil, silt, calcareous soil, loam, Tashmukhamedova et al. 1968). Cymarin and apocanno- clay, mineral soils around hot springs, and even side are also cytotoxic against certain human carcinomas occasionally peaty soil. Johnson et al. (1998) stated (Kupchan et al. 1964). Other historical medicinal uses that A. cannabinum usually grows in sandy or loamy include use as a cathartic, a diuretic, a stimulant, a soils; however, according to Robison and Jeffery (1972), diaphoretic, a febrifuge (lowers fever), a rheumatism the plant is seldom found in sandy soils with low remedy, and a treatment for gallstones (Dalby 2004). It fertility, and grows best in fertile, medium- or heavy- is held in regard by homeopathic practitioners and Felter textured soils. Dense infestations tend to be found in (1922), while describing its uses, stated: ‘‘No remedy in the low-lying, wet areas, but fairly high densities may still Eclectic materia medica acts with greater certainty than occur on drier upland soils (Becker 1981; Voss 1996). 982 CANADIAN JOURNAL OF PLANT SCIENCE

Fig. 5 DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 983

The range of soil pHtolerated is reported to be 4.5 7 colony survival and spread. The main root is 23 (10) (USDA-NRCS 2004); however, based on the numerous mm in diameter and can extend a number of meters. herbarium specimen labels indicating that this species The root system consists of a vertical primary and one grows in ‘‘calcareous soil’’, a higher pHtolerance is to many lateral horizontal roots from which secondary likely. vertical roots may arise (Frazier 1944). Primary roots of 2-yr-old A. cannabinum have been found to penetrate to (c) Communities in Which the Species Occurs * In depths of 4 m, while extending as much as 6 m from the Canada, the natural habitat of A. cannabinum appears parent plant (Frazier 1945; Becker 1981; Orfanedes et al. to be mainly along shores and flood plains. Information 1993). Lateral roots rarely attain a depth of more than on herbarium specimens indicates it growing in a wide 17 cm (Orfanedes et al. 1993) and grow 530 cm before variety of habitats including thickets, marshes, mea- secondary vertical roots develop (Doll 1994). Secondary dows, disturbed ground, roadside ditches, forest edges growth occurs from buds along the lateral roots (Frazier and openings (coniferous, mixed, deciduous and planta- 1944). Crown buds, located at the base of the stem, are tion), alvars, old fields, cultivated fields (oat, corn, also important for vegetative reproduction and begin soybean, potatoes, etc.), intertidal zones, prairies, aban- growth each spring or following damage to the stem. doned farm fields, sand dunes, ditches, talus slopes and sloughs. The plant is rarely a problem in conventional (b) Perennation * A perennial species, A. cannabinum, tillage systems because tillage constantly breaks the over-winters as a below-ground system of crown buds, rhizomes and roots (Curran et al. 1997). Buhler et al. rhizomes and roots, reemerging from buds each spring (1994) found similar results with higher dogbane den- (see Section 7d). Becker (1981) noted a University of sities in continuous corn than with a corn/soybean Nebraska study indicating that hemp dogbane seedlings rotation in both ridge- and no-till systems. Apocynum are capable of perennial regrowth within 10 to 41 d of cannabinum grows best in open spaces (Gleason and emergence, but various other studies suggest that the Cronquist 1991) and poorly in full shade (Balbach actual time is closer to 6 wk (Robison and Jeffery 1972; 1965). In non-agricultural settings, Muenscher (1951) Furrer et al. 1983). Schultz and Burnside (1979a) found plants in gravelly fields, meadows, waste places, observed a cyclical pattern in root and aerial stem and along streams, whereas Johnson et al. (1998) found regenerative capacity, with the highest activity occurring plants mainly in prairie river flood plains, terraces, and in spring and late fall and lowest activity occurring in roadside ditches. summer and early fall.

6. History (c) Physiology * In common with other perennial As mentioned in Section 3b, changing cropping systems weeds, protein and carbohydrate levels peak in the have favoured increased infestation in some regions in spring and fall, and are relatively low in the summer. recent years. For example, in Wisconsin, 6% of agri- Schultz and Burnside (1979a) showed that protein levels cultural extension agents ranked it as serious or very ranged from 4 to 5% in summer to from 7 to 9% in fall. serious in row crops and small grains in 1977, but this Protein and non-structural carbohydrate levels are had increased to 15% by 1994 (Doll 1995). Practices higher in lateral roots than crown roots (Schultz and contributing to this trend may include reduced tillage, Burnside 1979a). decreased use of phenoxy herbicides, reduced rates The thickness of the cuticle (measured as 305 mgcm2) of triazine herbicides and continuous row cropping on the adaxial leaf surface and (458 mgcm2) on the (Robison and Jeffery 1972; Wyrill and Burnside 1976b; abaxial surface and the presence of stomata only on Schultz and Burnside 1980; Becker 1981; Webster and the abaxial surface (320 stomata mm2) (Wyrill and Cardina 1999). Burnside 1976b) likely contribute to drought tolerance and resistance by the plants to penetration by herbi- 7. Growth and Development cides. Moreover, these workers measured epicuticular (a) Morphology * The development of the extensive wax thickness of 85 mgcm2 on the adaxial surface and root and rhizome system (Fig. 1B) is important for the 56 mgcm2 on the abaxial surface, noting the amount of weed’s survival. The aggressive spread and persistence of wax was 2.8 times greater and cuticle thickness 1.6 times the weed is most likely due to the large reserves of greater in A. cannabinum than in common milkweed. carbohydrates in the root system (Balbach 1965; Becker They attributed the lower absorption of glyphosate and Fawcett 1998), which serve as a major resource for and 2,4-D in A. cannabinum compared with common

Fig. 5. Distribution of Apocynum cannabinum in Canada plotted from specimens examined from the herbaria ACAD, ACK, ALTA, CAN, DAO, HAM, MMMN, MT, NFLD, NSPM, QFA, QUE, SASK, TRT, TRTE, UNB, UVIC, UWO, UWPG, WAT, WIN, and V. Acronyms according to Holmgren et al. (1990). A. distribution of A. cannabinum var. cannabinum and var. hypericifolium plotted from 1642 specimens; B. distribution of Apocynum cannabinum var. cannabinum plotted from 230 specimens, including those which could not be confidently placed in either subspecific taxon; C. distribution of putative hybrids between Apocynum cannabinum and Apocynum androsaemifolium (A.floribundum) plotted from 88 specimens. 984 CANADIAN JOURNAL OF PLANT SCIENCE milkweed to the greater thickness of the cuticle and occur 10 wk after full bloom (Schultz and Burnside epicuticular wax. 1979a; Becker 1981). Apocynum cannabinum has been shown to be more Carbohydrate levels in the roots, mainly in the form susceptible to herbivory following touching or handling of starch, decline with vegetative growth in the spring, of field plants by humans (experimenter) or by the reach seasonal lows during flowering, and increase until experimenter visiting test plots containing the plant dormancy when levels are the highest (Becker and (Cahill et al. 2001, 2002; Niesenbaum et al. 2006). The Fawcett 1998). The decline of stored carbohydrate latter is believed to reduce above-ground competition for during vegetative growth and flowering correlates with light through trampling of neighbouring vegetation, thus the high energy demands of these life stages (Becker and increasing the visibility or apparency of A. cannabinum Fawcett 1998). plants to herbivores. Touching or handling the plants increased oviposition by herbivores and altered the (e) Mycorrhiza * Rickerl et al. (1994) included defense chemistry or nutrition of plants, with the latter A. cannabinum in a study investigating mycorrhizal leading to increased emergence of the stem borer Papai- colonization of wetland plants in South Dakota. They pema baptisiae Bird (a noctuid moth) (Cahill et al. 2002). recorded approximately 29% mycorrhizal colonization Mid-vein cutting has been suggested to have evolved of A. cannabinum in a hydric soil (but without surface in insects as a countermeasure to deactivate induced leaf water). latex or cardenolide defences in milkweeds and dog- banes. In field experiments in Nebraska, transverse 8. Reproduction cutting of the leaf mid-vein in A. cannabinum reduced Reproduction occurs via seed and an extensive system of several gas exchange parameters, but only downstream roots and rhizomes (Orfanedes et al. 1993). Local (distal) from the injury location (Delaney and Higley populations may propagate through a mixture of sexual 2006). Injury was most severe as the location ap- and vegetative reproduction or entirely clonally (Ran- proached the petiole, suggesting that the effects of vein som et al. 1998b). cutting on leaf physiology would be more severe than just partial leaf tissue consumption of the plant. (a) Floral Biology *The small, pale flowers (Fig. 1C, 4) Lee et al. (1972) maintained tissue cultures of A. are not adapted for specialized pollinators. Lipow and Wyatt (1999) provided a definitive description of the cannabinum initiated from seedlings for 3 yr on solid floral biology, and noted that pollination is only media, in flask suspension, and in a New Brunswick 5-L mediated through insects attracted to the fragrant fermentor. They recorded an average growth rate of flowers and abundance of nectar. Autogamy is pre- 5.33 g L1 d1 in the fermentor. The tissue cultures vented by the morphology of the pistil, where the stigma produced glycosides such as cymarin, which may be is located on the underside of the style head; however, if useful as medicines (see Section 3b). self-pollination occurs, late-acting self-incompatibility results in termination of embryo development (Lipow (d) Phenology * Growth is initiated each spring from and Wyatt 1999). Although there are large numbers of crown buds and rhizomes (Robison and Jeffery 1972). insect visitors, they represent only 25 species and most Emergence from crown buds was observed to occur at carry little or no pollen (Johnson et al. 1998). Lipow and soil temperatures of 17198C in Nebraska (Schultz and Wyatt (1999) determined that floral structure limits the Burnside 1979a). Within 28 wk from the seedling stage, number of effective pollen distributors. Since the insect roots were as long as 3 m; after two years of growth, the proboscis must be slipped between the stamens, con- same plants’ roots extended up to 4 m in length and 5.4 tacting the stigma first, previously collected pollen is m radially (Robison and Jeffery 1972). Hitchcock and deposited before new additional pollen is picked up. Clothier (1898) recorded a single horizontal root mea- Often the narrow space does not allow enough room to suring 8.8 m long. The flower bud stage occurs withdraw the proboscis and insects have been found approximately 47 wk after shoot emergence (Schultz dead within the flowers of A. cannabinum (Lipow and and Burnside 1979a; Becker 1981). In Colorado, Wyatt 1999). Johnson et al. (1998) observed that flowering began in mid-June (sometimes in May) and continued through (b) Seed Production and Dispersal * Seeds (Fig. 1E, F) are August or until September. Plants do not flower in the set in summer and mature in the fall (USDA-NRCS 2004) first year after seedling emergence, but flower readily in in long pods (follicles) (Fig. 1D). The follicles may contain the second season (Frazier 1945). Webster and Cardina up to 200 seeds (Doll 1994). In Nebraska, the number of (1999) observed that 75% flowering was attained at a developing seeds per follicle increased rapidly between similar calendar date in 1997 (July 02) and 1998 (June weeks 4 and 5 after flowering, with seed weight tripling 30) in Ohio, despite a large variation in accumulated from 4 to 13 wk after flowering (Schultz and Burnside growing degree units (GDU). Early flowering, full 1979a). Evetts and Burnside (1972) found a range of 80 to bloom and follicle initiation proceed at 1-wk intervals 200 seeds per follicle in Nebraska. Schultz and Burnside following the flower bud stage and the first viable seeds (1979a) recorded an average number of 81 seeds per DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 985 follicle in naturally pollinated field-grown plants from 4.3 cm in coarse-textured soils, but only 3.3 cm in fine- Nebraska. The average number of follicles per plant textured soils. Although seeds may germinate between produced in Nebraska ranged from 150 in a monotypic 10 and 408C, Evetts and Burnside (1972) reported nursery stand to 2 in soybean fields (Schultz and Burnside optimal seedling growth between 20 and 258C. The 1979a). Lipow and Wyatt (1999) recorded an average of highest percentage seed germination recorded by 46.7933.8 seeds per follicle in hand-pollinated green- Thompson (1972) was at 358C. Similarly, Webster and house plants in Georgia. This lower number relative to Cardina (1999) found maximum germination occurred results from Nebraska may be due to the inefficiency of at 348C when seeds from Ohio populations were their hand pollination since 162.9965.7 seeds developed subjected to alternating temperatures. They also found in two naturally pollinated follicles within a flower when that germination followed a sigmoidal pattern for the greenhouse plants were placed in the field. Lorenzi constant temperatures, whereas with alternating tem- and Jeffery (1987) estimated production of approximately peratures there was a linear relationship between 200 seeds per follicle in populations from across the germination and maximum daily temperature between United States. When grown in competition with most 15 and 348C. agronomic crops, A. cannabinum does not produce many Evetts and Burnside (1972) obtained a high germina- viable seeds (Schultz and Burnside 1979a) and depends tion percentage with ample moisture (91% germination primarily on vegetative reproduction (Gerhards et al. at 0 MPa of osmotic pressure), but seeds failed to 1997). germinate at 0.91 MPa or higher. Similarly, Webster The seeds with their tuft of white silky hairs are and Cardina (1999) observed a linear decline in germi- approximately 4-6 mm long and 0.75 mm wide and nation going from 80% at 0 MPa to 4% at 1.0 MPa, adapted to wind dispersal (Robison and Jeffery 1972; with seed germination decreasing rapidly at osmotic Doll 1994). The ability of seeds to float facilitates potentials below 0.2 MPa. potential dispersal by water (Evetts and Burnside 1973). Burnside et al. (1981) concluded that owing to (d) Vegetative Reproduction * Extensive vegetative poor survival of seed in soil, seed dispersal plays a role reproduction and spread occurs by the horizontal roots in establishing new populations, but new plants are and rhizomes (Woodson 1930). New shoots may emerge primarily established by vegetative propagation. from either crown buds or from buds forming on the horizontal roots and rhizomes (Woodson 1930; Frazier (c) Seed Banks, Seed Viability and Germination * 1944; Orfanedes and Wax 1991). Frazier (1944) con- Jeffery and Robison (1969) found that in Nebraska ca. ducted a series of experiments to elucidate the vegetative 50% of the seeds initially released from the follicle are growth of A. cannabinum. Small feeding roots that grew dormant. In contrast, Burnside et al. (1981) found that along the main vertical root that were in a suitable A. cannabinum seeds from Nebraska had ‘‘essentially no position (i.e., mainly in the top 18 cm of soil) grew more seed dormancy’’, with most buried seeds germinating robust and became permanent lateral roots. Buds within a year of burial. Four years of burial reduced the produced along this permanent lateral root formed a germination of seeds to below 1%. In Nebraska, Schultz secondary vertical root along with a shoot or rhizome. and Burnside (1979a) examined seed weight and viabi- After 28 wk of growth without competition, Frazier lity for seeds harvested at weekly intervals after flower- (1944) found four permanent lateral roots with a range ing. They recorded an increase in seed weight from 199 up to 3.5 m. By the second year, the roots had mg per 100 seeds 4 wk after full bloom to 736 mg per 100 penetrated to 4.2 m deep and 5.9 m outwards (Frazier seeds 13 wk after full bloom. The first seeds to germinate 1945). Webster and Cardina (1999) demonstrated that were those harvested 10 wk after full bloom, and the shoot appearance could be predicted based on accumu- maximum germination attained was 38% for seeds lated growing degree units (GDU), with 50% of shoots harvested 14 wk after full bloom. Lipow and Wyatt emerging after about 280 GDU. (1999) obtained germination of 93.7% of the seeds produced via hand-pollination. 9. Hybrids After 21 mo of burial in a Nebraska field study, Evetts Hybridization occurs frequently among species in the et al. (1972) found that no A. cannabinum seeds genus Apocynum, complicating taxonomic classification germinated. Germination increased 41% when seeds and increasing intraspecific variability (Woodson 1930; were placed in the light, without any scarification, but Anderson 1936; Balbach 1965; Voss 1996). Hybrids scarifying seeds and subjecting them to either light or derived from Apocynum androsaemifolium and Apocy- dark increased germination (Robison and Jeffery 1972). num cannabinum, are sometimes designated as A. Unfortunately, these workers did not indicate whether floribundum Greene (A. medium Greene) and are they used freshly harvested seeds for these studies. Seeds found throughout the sympatric distribution of the planted at 1 cm depth resulted in 70% emergence, while parental species (Fig. 5C). Plants identified by Anderson emergence is greatly reduced at increasing depths (1936) as either A. cannabinum or A. androsaemifolium (Robison and Jeffery 1972; Thompson 1972). Evetts bred true, whereas offspring of A. floribundum and Burnside (1972) observed maximum emergence at (F2 generation) segregated and displayed some traits 986 CANADIAN JOURNAL OF PLANT SCIENCE that resembled those of the parental species, but other ha1) resulted in greater stem growth and more leaf traits (e.g., pollen viability) were substantially different. pairs than the high fertility level treatment (224 kg N Johnson et al. (1998) identified six isozyme loci diag- ha1) (Robison and Jeffery 1972). Ransom et al. nostic for A. cannabinum and A. andorsaemifolium, and (1998a) collected plants from 16 populations in both found four putative hybrids which were heterozygous. Michigan and Illinois and subsequently planted them in Plants identified as hybrids exhibited lower seed set and a common garden in each state. These workers recorded produced smaller sized seed than parental species. greater shoot number, shoot height and ground area Balbach (1965), on the other hand, was unable to covered for ecotypes grown in Michigan as compared germinate seeds from plants intermediate between A. with those grown in Illinois. Mean shoot dry weights cannabinum and A. androsaemifolium. were greater in Illinois plants, although considerable variation was observed within ecotypes from Illinois. 10. Population Dynamics Leaf shape also differed, with Michigan-grown plants Populations of A. cannabinum have been increasing exhibiting longer leaves in proportion to width as throughout the north-central, eastern, and the Great compared with leaves produced in Illinois, and was Plains regions of the United States (Robison and Jeffery likely due to site differences. In general, Ransom et al. 1972), but increased prevalence of this species in Canada (1998a) observed a great deal of variation in almost has not been reported. Usually, A. cannabinum is every morphological attribute they measured, presum- distributed in patches, and is rarely found to infest ably reflecting both a high degree of phenotypic entire fields (Robison and Jeffery 1972; Schultz and plasticity and considerable genetic differences among Burnside 1979a). Coffman and Frank (1988) observed ecotypes. that A. cannabinum patches in no-till corn in Maryland Apocynum cannabinum is not a strong competitor in tended to remain in approximately the same locations small grains, hay, alfalfa or winter wheat (Becker 1981), over a 5-yr period. Patch growth and movement has but tends to grow faster than row crops, especially in been studied fairly intensively. Webster et al. (2000b) spring (Furrer et al. 1983). In Nebraska, corn also found that patches in Ohio with an initial area less than competes well with this weed whereas soybeans and 23 m2 doubled in one year, whereas Gerhards et al. grain sorghum do not (Schultz and Burnside 1979a). (1997) observed that patch sizes remained stable for 4 yr Within corn, sorghum and soybean fields, the average in Nebraska crop fields. In the latter study, A. canna- number of plants ranged from 39 700 to 76 500 ha1 binum was more stable than the three annual weeds with irrigated fields containing approximately 25 000 monitored, being largely unaffected by various weed more plants ha1 than dryland fields (Schultz and control practices (Gerhards et al. 1996). The movement Burnside 1979a). The latter authors also found that of A. cannabinum between fields is often facilitated by the highest infestations were in oats and soybeans and tillage equipment dragging roots, rhizomes and crown the lowest in alfalfa and winter wheat. In weedy check fragments (Schultz and Burnside 1979a). The patch plots maintained by Glenn et al. (1997) within a corn borders are established early in the growing season crop in Maryland, A. cannabinum populations increased and although the patches grew 2.43.5% per day in May only 10% over 2 yr, as compared with 123% for and June, 50% of the final patch size was already Allegheny blackberry (Rubus allegheniensis Porter) and determined in mid-May (Webster et al. 2000b). The 177% for lamb’s-quarters (Chenopodium album L.). potential for a serious infestation can be seen in the Current crop production systems favour the increase relative abundance, where 60% of the fields evaluated in in A. cannabinum populations. Removal of annual Nebraska had a population of 125 plants ha1,25% weeds via pre-emergence herbicides decreases competi- had 26250 plants ha1, and 15% had 2512500 plants tion and encourages abundant growth of this perennial ha1 (Schultz and Burnside 1979a). The ability of species (Schultz and Burnside 1979a; Orfanedes and individual plants to spread may be strongly influenced Wax 1991). by genotype, as more aggressive plants were shown to Thompson (1972) reported that the number of days occupy 19 times more area than the least aggressive needed for the first shoot to occur after clipping when grown in common garden experiments in Illinois decreased as days from planting to clipping increased; and Michigan (Ransom et al. 1998a). the regrowth percentage of the weed clipped at the Although A. cannabinum ordinarily attains heights soil line increased as days from planting to clipping between 30 and 60 cm, it may occasionally produce increased. shoots over 150 cm, with its growth strongly affected by environmental conditions (Woodson 1930). Robison 11. Response to Herbicides and Other Chemicals and Jeffery (1972) recorded effects of soil type and No specific Canadian studies on herbicidal control of A. fertility level on plant growth in a greenhouse study. cannabinum have been reported; thus, all findings are Higher fertility generally resulted in taller and heavier based on studies carried out in the United States. shoots, longer branches, more leaf pairs, and heavier There is a lack of consistency in the reported roots. For one of the soil types tested (sandy soil), effectiveness of chemical applications on A. cannabinum, however, the moderate fertility treatment (112 kg N and herbicides often fail to control the weed (Evetts and DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 987

Burnside 1973; Schultz and Burnside 1979b; Glenn is one of the most effective herbicides against A. and Anderson 1993; Ransom and Kells 1998). Schultz cannabinum (Webster and Cardina 1999). and Burnside (1980) attributed the differences in control to various edaphic, climatic and biotic factors. 2,4-D and Dicamba * The herbicides 2,4-D (1120 g a.i. Welch and Ross (1997) conducted a common garden ha1) and dicamba (280 g a.i. ha1) together work well pot study of root and shoot growth in response to the to suppress growth of A. cannabinum, but may require an herbicides glyphosate, glufosinate, and 2,4-D. Shoot additional application in the second year to maintain growth was reduced more than root growth, and some suppression (Roeth 1977). In one study, 2,4-D alone (560 healthy root tissue remained in all treatments. However, g a.i. ha1) was found to control 7989% of A. single applications of either glyphosate (1262 g a.i. cannabinum (Orfanedes and Wax 1991). However, as in ha1) or glufosinate (400 g a.i. ha1) resulted in more the case of glyphosate, diffusion of 2,4-D across the shoot dry weight than untreated plants. There was a cuticle is limited (Wyrill and Burnside 1976b). Wyrill and reduction in shoot dry mass from a single application of Burnside (1976b) pointed out that the lack of 2,4-D 2,4-D (1121 g a.i. ha1). The only treatment that metabolism in the roots of A. cannabinum explains its prevented the formation of new shoots was a split susceptibility to the chemical. In corn, Bradley and application of glyphosate, where a second application of Hagood (2001) found that 2,4-D with either primisul- 1262 g a.i. ha1 was applied to surviving shoot growth. furon-methyl (39 g a.i. ha1) or nicosulfuron (35 g a.i. For all other treatments, Welch and Ross (1997) ha1) provided better control than dicamba (560 g a.i. concluded that even if A. cannabinum was controlled ha1) with either primisulfuron-methyl or nicosulfuron. during the growing season, it would be capable of Glenn and Anderson (1993) found that tank mixtures of re-establishing new plants subsequently from surviving nicosulfuron (3162 g a.i. ha1) with 2,4-D (560 g a.i. root segments. ha1) or dicamba (280 g a.i. ha1) gave 72100% control, while triclopyr (140280 g a.i. ha1) and 2,4-D Glyphosate *Control of A. cannabinum with glyphosate (280560 g a.i. ha1) mixtures gave 7298% control. may be limited, when compared with other perennial Kalnay and Glenn (2000) agreed with Glenn and weeds, due to reduced foliar uptake. Wyrill and Burn- Anderson (1993) and showed that dicamba (70 g a.i. side (1976b) recorded that only 0.1% of applied ha1)nicosulfuron (35 g a.i. ha1) increased translo- glyphosate diffused through the leaf cuticle of 5- to cation of both herbicides more than either one alone. The 6-wk-old seedlings. Richard and Slife (1979) found that ester form of 2,4-Ddicamba provided erratic control, adjuvants increased the amount of glyphosate absorbed but two studies (Schultz and Burnside 1979b; Ransom in the first half hour by 3.75 times, but did not extend and Kells 1998) found that the 2,4-D ester (40140 g a.e. the period or amount of absorption. Barnes and ha1) performed better than the 2,4-D amine (70280 g Brenchley (1972) observed that glyphosate (1700 a.e. ha1). For best control, Becker and Fawcett (1980b) and 3400 g a.i. ha1) was effective when applied to recommended applying in late June, while Roeth (1977) plants in the early bud stage (plants 1.2 to 1.5 m tall), recommended September applications. but was ineffective at the late flowering stage (plants 1.5 to 2.1 m tall). The addition of ethoxylated amines at up Paraquat * Bradley and Hagood (2001) recommend to 0.3% (wt/vol) concentrations acted as effective using paraquat (260 g a.i. ha1) to control A. cannabi- surfactants, improving uptake and increasing glyphosate num in established alfalfa fields. toxicity (Wyrill and Burnside 1977). In contrast, Doll (1997) found that glyphosate applied to A. cannabinum Fluroxypyr and Clopyralid * Although sensitive to in the vegetative and bud stages was less effective at all fluroxypyr, A. cannabinum is not sensitive to clopyralid rates used (6301680 g a.e. ha1) than glyphosate (560 g a.e. ha1), possibly because of differences at the applied in the early and full flower stages. The 630 g activity site (Orfanedes and Wax 1991; Orfanedes et al. a.e. ha1 rate seldom gave 90% control, while rates of 1993) or, because the latter is highly water-soluble, its 840 g a.e. ha1 or more almost always provided more penetration of the thick cuticular wax is inhibited than 90% control. Glyphosate application (1130 or 2260 (Orfanedes et al. 1993). Resprouting of A. cannabinum g a.i. ha1) resulted in approximately 90% and 85% plants near the base of controlled shoots has been control when applied in early summer and fall, respec- observed 48 wk after application of fluroxypyr (70280 tively (Fawcett and West 1978; Curran et al. 1997). g a.i. ha1) (Orfanedes and Wax 1991). Increasing glyphosate rates did not improve control in corn, nor did applications in combination with 2,4-D Thiocarbamates * Thiocarbamates may suppress re- and dicamba (Curran et al. 1997). Studies conducted by growth from either crown or lateral roots (Schultz and Schultz and Burnside (1978b,c,d) found that impurities Burnside 1979b; Becker 1981). According to Schultz and in water, especially high levels of Ca2 reduced the Burnside (1979b), preplant applications of thiocarba- phytotoxicity of glyphosate, whereas monovalent mate herbicides (e.g., butylate) aided in control of the cations had no effect. In general, however, glyphosate weed by delaying emergence, suppressing vigour, and 988 CANADIAN JOURNAL OF PLANT SCIENCE possibly allowing subsequent foliar applications of 2,4- grow from dormant below-ground buds (Glenn and D to be more effective, with these effects persisting for Anderson 1993). about 2 mo.

Nicosulfuron * Nicosulfuron (35 g a.i. ha1) was shown 12. Response to Other Human Manipulations to have similar efficacy as dicamba (560 g a.i. ha1), No-till systems, more than chisel or moldboard, often and the efficacy of both was enhanced in combination experience infestations because the under-ground root with 2,4-D (280 g a.i. ha1) (Glenn et al. 1997). system is left intact, which allows new plants to develop from lateral root buds (Becker 1981; Buhler et al. 1994). Primisulfuron * Doll (1994) found 8090% control with However, reduced density of established A. cannabinum primisulfuron (20 g a.i. ha1) when plants were 1230 populations through tillage may be accompanied by cm and better at stem heights up to 61 cm. Curran et al. increased area of infestation due to root fragmentation 1 (1997) also tested primisulfuron (20 g a.i. ha )with and dispersal throughout the tilled area (Woodson 1930; 1 dicamba (282 g a.e. ha ) and found control equal to Robison and Jeffery 1972; Schultz and Burnside 1979b). fall applied glyphosate (85%). Glenn et al. (1997) Doll (1995) recommended using no-till systems where 1 reported that primsulfuron (20 g a.i. ha ) was less possible because tillage may increase the already vari- 1 effective than nicosulfuron (35 g a.i. ha ) or dicamba able early emergence, while no-till systems allow the 1 (560 g a.i. ha ). plants to reach a more susceptible stage when postemer- gence herbicides are normally applied. Likewise, Becker Glufosinate * Although a single application of glufosi- 1 and Fawcett (1980a) concluded that no tillage, as nate (400 g a.i. ha ) in a greenhouse experiment failed compared with moldboard plough, chisel plough or to provide adequate control, a split application, whereby disk systems would result in the least persistence in the same herbicide dosage was re-applied to surviving terms of numbers of plants (but not plant vigour). Fall shoots, resulted in a 79% reduction in shoot volume chisel ploughing may only improve early-season control, (Welch and Ross 1997). while spring chisel ploughing may increase biomass 1 when herbicides are not used (Curran et al. 1998). Amitrole * Amitrole (5602240 g a.i. ha ) provided Postemergence herbicide applications do not tend to poor control in all studies (Schultz and Burnside 1978g; correspond with susceptible stages of A. cannabinum, Schultz and Burnside 1979b). and thus reduced tillage systems may favour this species over other weeds (Triplett 1985). Similarly, cultivation Timing of Application of Certain Herbicides * Most should be timed to correspond to the early seedling stage studies have concluded that fall application is more ( 25 cm tall) before they are capable of forming new effective than spring (Robison and Jeffery 1972; Roeth B 1977; Becker 1981; Furrer et al. 1983; Curran et al. 1997; shoots from root buds (Doll 1995). Plant vigour, rate of Becker and Fawcett 1998). Fawcett and West (1978) flowering, and maturation are decreased with increasing found almost no control if herbicides are applied after severity of tillage (Becker and Fawcett 1980a). Shallow corn harvest and Furrer et al. (1983) cautioned against cultivation at 2- to 3-wk intervals for 2 to 3 yr will spraying after frost- or drought-induced yellowing in the eventually deplete the energy reserves in the roots leaves. Doll (1994) found that spot treating or applying (Schultz and Burnside 1979b; Becker 1981). pre-harvest in soybeans was effective. Spring spraying Crop rotation with alfalfa and frequent clipping for has been recommended during the early reproductive hay will diminish the competitive effects of A. cannabi- stage to early flowering stage when most of the growth num (Evetts and Burnside 1973; Becker 1981). In a and phloem movement is occurring (Furrer et al. 1983; greenhouse clipping experiment, Robison and Jeffery Orfanedes and Wax 1991; Orfanedes et al. 1993). Early (1972) found that regrowth occurred only after plants post-emergence applications of herbicides will not were 41 d old and that plants less than 10 cm in height or inhibit regrowth from perennial roots (Becker 1981; with fewer than eight leaf pairs did not regrow. Schultz Furrer et al. 1983; Ransom and Kells 1998). On the and Burnside (1978e,f) found that regrowth of clipped other hand, seedlings were susceptible to a wide range of plants in a greenhouse decreased if clipping occurred 1 d soil-applied herbicides, i.e.,80% control was achieved after spraying with either 2,4-D or glyphosate, and with clomazone (840 g a.i. ha1), sulfentrazone (220 g remained depressed if clipping was delayed up to 2 wk a.i. ha1), metribuzin (280 g a.i. ha1), atrazine (840 g after application of high rates of 2,4-D (105 g ha1). a.i. ha1), flumetsulam (40 g a.i. ha1), cloransulam (30 Rotation with winter wheat allows for increased control g a.i. ha1), imazaquin (140 g a.i. ha1), and metribuzin of A. cannabinum patches (Evetts and Burnside 1973; (180 g a.i. ha1) plus chlorimuron (30 g a.i. ha1) Furrer et al. 1983). Evetts and Burnside (1973) recom- (VanGessel 1999). Often, the timing of pre-emergent mended that if this species still persisted in a field after herbicide application does not correlate with susceptible competition with winter wheat, periodic cultivation stages of perennial weeds, therefore, only the top growth could serve to further deplete food reserves and even- of the weeds is affected, while the weed continues to re- tually cause mortality. DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 989

13. Response to Herbivory, Disease and Higher America: Aecidium apocyni Schwein. (North Carolina), Plant Parasites Bionectria apocyni (Peck) Schroers & Samuels (Nec- (a) Herbivory tria apocyni Peck) (New York), Colletotrichum trunca- tum (Schwein.) Andrus & W.D. Moore (Illinois), (i) Mammals * No information was located. Fusarium oxysporum Schltdl. (Delaware), Macropho- mina phaseolina (Tassi) Goid. [M. phaseoli (Maubl.) (ii) Birds * No information was located. S.F. Ashby] (Illinois), Pestalozziella andersonii Ellis & Everh. (Montana), Phyllosticta apocyni Trel. (Florida, (iii) Insects * Schultz and Burnside (1978a) in Nebraska Mississippi, New Jersey, New York, Oklahoma, Wis- observed four different Lepidoptera feeding on the foliage consin), Phymatotrichopsis omnivora (Duggar) Henne- of A. cannabinum, which caused enough defoliation in bert (Phymatotrichum omnivorum Duggar) (Texas), some cases to decrease the effectiveness of foliar applied Puccinia smilacis Schwein. (Illinois, Kansas, Maryland, herbicides. The four insects found were the woolly bear North Carolina, Tennessee, Virginia, Wisconsin), Sep- moth Ammalo tenera Hubner (Arctiidae), Pyrausta futia- toria littorea Sacc. (Kansas, Mississippi, North Dakota, lis Lederer (Pyralidae), the leafroller Aphelia pallorana Nebraska, Ohio), Stagonospora apocyni (Peck) Davis Robinson (Tortricidae), and the milkweed tiger moth (Indiana, Minnesota, New York, South Dakota, Virgi- Euchaetes egle Drury (Arctiidae). Most foliar damage was nia, Wisconsin) and Thanatephorus cucumeris (A.B. caused by A. tenera and P. futialis and the extent of Frank) Donk. (Washington). Venkatasubbaiah et al. defoliation varied from 2 to 95% (Schultz and Burnside (1992) identified a fungus found extensively on A. 1978a). Another lepidopteran specializing on A. cannabi- cannabinum in Virginia as Stagonospora apocyni. All of num (and the genus Asclepias), the dogbane tiger moth the toxins produced by S. apocyni (citrinin, mullein, Cycnia tenera Huebner (Arctiidae) was observed causing tyrosol and aactyloricinol) caused necrosis on leaves of considerable damage to A. cannabinum in Pennsylvania hemp dogbane. Plants inoculated with S. apocyni had (Cahill et al. 2002). Cahill et al. (2002) also recorded the small black lesions, and heavily infected leaves abscised. dogbane beetle Chrysochus auratus Fabricius (Chrysome- lidae) feeding on A. cannabinum in Pennsylvania. They (ii) Bacteria * No information was located. also noted that A. cannabinum damage due to these herbivores increased when nearby vegetation was (iii) Viruses * No viruses have been recorded for any trampled and that touching or handling of A. cannabinum species of Apocynum in the VIDE database (Brunt et al. plants resulted in higher incidence of emergence holes 1996 onwards). from the lepidopteran stem borer Papaipema baptisiae Bird (Noctuidae). Panic moth, Saucrobotys futilalis (c) Higher Plant Parasites * No information was Lederer (Pyralidae), larvae have also been documented located. to feed on A. cannabinum foliage in central New York State (Grant 2007). Other lepidopterans documented to use A. cannabinum as a host in Nearctic regions of North ACKNOWLEDGEMENTS America include Marmara apocynella Braun (Gracillar- The curators are thanked for the loan of specimens from iidae), zebra caterpillar moth Melanchra picta Harris the following herbaria: ACAD, ACK, ALTA, CAN, (Noctuidae), and the snowberry clearwing moth Hemaris DAO, HAM, MMMN, MT, NFLD, NSPM, QFA, diffinis Boisduval (Sphingidae) (Natural History Mu- QUE, SASK, TRT, TRTE, UNB, UVIC, UWO, seum 2008). Lepidopterans reported to use Apocynum UWPG, WAT, WIN, and V. The help provided by spp. as host plants in Nearctic regions include the Oregon Scott Morris and Marisa Isaacson to locate references is Cycnia moth Cycnia oregonensis (Stretch) (Arctiidae) and also acknowledged. the six-spotted gray moth Spargaloma sexpunctata Grote (Noctuidae) (Natural History Museum 2008). Anderson, E. 1936. An experimental study of hybridization in the genus Apocynum. Ann. Mo. Bot. Gard. 23: 159168. (iv) Nematodes and Other Invertebrates * No informa- Anonymous. 1970. Selected weeds of the United States. US tion was located. Dep. Agric., Agric. Res. Serv. Agric. Handb. No. 366. 463 pp. Anonymous. 2009. [Online] Available: http://www.allfiberarts.- (b) Diseases com/cs/dyeplants.htm [2009 Apr. 17]. Babcock, P. A. and Carew, D. P. 1962. Tissue culture of the (i) Fungi * Fungi reported from A. cannabinum Apocynaceae. I. Culture requirements and alkaloid analysis. (including A. sibiricum) in Canada are Cercosporella Lloydia 25: 209213. Balbach, H. E. 1965. Variation and speciation in populations apocyni (Ellis & Kellerm.) Trel., Cylindrosporium apoc- of Apocynum in North America. Ph.D. thesis, University of yni Ellis & Everh., C. sibiricum Dearn. & Bisby, Puccinia Illinois, Urbana, IL. 95 pp. seymouriana Arthur and Septogloeum apocyni Peck Barnes, D. and Brenchley, R. 1972. Response of hemp dogbane (Conners 1967). Farr et al. (2004) listed additional to the isopropylamine salt of glyphosate (MON-2139). Proc. species recorded on A. cannabinum elsewhere in North North Central Weed Cont. Conf. 27:5455. 990 CANADIAN JOURNAL OF PLANT SCIENCE

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Pages 2640 in A. F. Weise, leaves ovate to broadly elliptic, widely spreading or ed. Weed control in limited tillage systems. Weed Sci. Soc. Am. drooping; seedsB3 mm long ...... A. andro- Monogr. 2. saemifolium Triplett, G. B., Jr. and Lytle, G. D. 1972. Control and ecology of weeds in continuous corn grown without tillage. Weed Sci. 1. Flowers terminal, rarely axillary; calyx about 1/2 or 20: 453457. more as long as corolla; corolla (2) 2.54.5 (6) mm long, Turner, N. J., Bouchard, R. and Kennedy, D. I. D. 1980. petals erect, white to greenish; leaves oblong to broadly Ethnobotany of the Okanagan-Colville Indians of British Columbia. British Columbia Provincial Museum, Victoria, lanceolate, usually ascending or slightly spreading, but BC. Occasional Paper No. 21. never drooping; seeds3 mm long ...... A. USDA-NRCS. 2004. The PLANTS Database, Version 3.5. cannabinum.Goto2 National Plant Data Center, Baton Rouge, LA. [Online]. Available: http://plants.usda.gov [2008 Apr. 17]. 2. Leaves in the middle of the stem with blades tapering Van der Laan, F. M. and Arends, J. C. 1985. Cytotaxonomy of to a petiole3 mm long ...... A. cannabinum var. Apocynaceae. Genetica 68:335. cannabinum VanGessel, M. J. 1999. Control of perennial weed species as seedlings with soil-applied herbicides. Weed Technol. 13: 425 428. 2. Leaves in the middle of the stem with blades rounded to Venkatasubbaiah, P., Baudoin, A. B. A. M. and Chilton, W. S. cordate at the base, often clasping the stem, petiole 1992. Leaf spot of hemp dogbane caused by Stagonospora usuallyB3 mm long .... A. cannabinum var. hypericifo- apocyni, and its phytotoxins. J. Phytopathol. 135: 309316. lium