The biology of Canadian weeds. 135. Lonicera japonica Thunb.
Transcription
The biology of Canadian weeds. 135. Lonicera japonica Thunb.
The biology of Canadian weeds. 135. Lonicera japonica Thunb. Brendon M. H. Larson1, Paul M. Catling2, and Gerald E. Waldron3 1Department of Environment and Resource Studies, University of Waterloo, Waterloo, Ontario, Canada N2L3G1; 2Biodiversity, National Program on Environmental Health, Agriculture and Agri-Food Canada, Research Branch, Saunders Bldg., Central Experimental Farm, Ottawa, Ontario, Canada K1A 0C6; 37641 County Road 20, R. R. #1, Amherstburg, Ontario, Canada N9V 2Y7. Received 18 April 2006, accepted 14 December 2006. Larson, B. M. H., Catling, P. M. and Waldron, G. E. 2007. The biology of Canadian weeds. 135. Lonicera japonica Thunb. Can. J. Plant Sci. 87: 423–438. Japanese honeysuckle (Lonicera japonica Thunb.) is a twining semi-evergreen vine native to Japan, Korea and eastern China. Over the past 150 yr it has been introduced as an ornamental and become established in temperate and tropical regions worldwide. It was first discovered in Canada in 1976 in southwestern Ontario woodlands and has since been found growing without cultivation in 15 localities. While L. japonica does not occur very frequently in southern Ontario, climate change models suggest that it may become more abundant in this region. Its predominance elsewhere derives from morphological and physiological characteristics that allow it to be particularly successful in the edge habitats of fragmented landscapes. Through extensive vegetative propagation and competitive ability it occupies space which may otherwise host a diverse native flora. The plant has many uses in Asian medicine and is a popular ornamental, but has been prohibited in some regions due to its displacement of other species. A combination of cutting and foliar application of glyphosate has proven to be an effective control method in some circumstances. Planting of L. japonica should be discouraged and horticulturalists should consider alternative attractive vines. The spread of L. japonica should be monitored in Ontario and control of newly established populations should be considered to avoid costly large scale control in the future. Key words: Invasive species, Lonicera japonica, weed biology, climate change Larson, B. M. H., Catling, P. M. et Waldron, G. E. 2007. La biologie des mauvaises herbes au Canada. 135. Lonicera japonica Thunb. Can. J. Plant Sci. 87: 423–438. Le chèvrefeuille du Japon (Lonicera japonica Thunb.) est une vigne volubile mi-sempervirente originaire du Japon, de la Corée et de l’est de la Chine. Introduite il y a 150 ans comme plante ornementale, elle s’est implantée dans toutes les régions tempérées et tropicales de la planète. L’espèce a été découverte pour la première fois au Canada en 1976, dans des boisés du sud-ouest de l’Ontario. Depuis, on la retrouvée à 15 endroits sans qu’elle y ait été plantée. Bien que L. japonica ne se rencontre pas souvent dans le sud de l’Ontario, les modèles du changement climatique laissent croire qu’elle pourrait devenir plus abondante dans cette région. Ailleurs, on doit sa prédominance à ses caractéristiques morphologiques et physiologiques qui lui permettent de prospérer dans les habitats à la lisière des reliefs morcelés. Une forte multiplication végétative et une bonne compétitivité lui permettent d’occuper les espaces où se développerait normalement une flore indigène plus diversifiée. Cette plante a maints usages dans la pharmacopée asiatique et est populaire en horticulture, mais on en a interdit la culture dans certaines régions à cause de sa propension à supplanter d’autres espèces. La coupe combinée à l’application de glyphosate s’avère efficace comme méthode de lutte dans certaines circonstances. On déconseille aux horticulteurs de planter L. japonica en leur suggérant d’opter pour d’autres vignes aussi attrayantes. Il conviendrait de surveiller la propagation de L. japonica en Ontario et de détruire les nouveaux peuplements si l’on veut s’épargner une lutte plus ardue et plus coûteuse dans l’avenir. Mots clés: Espèce envahissante, Lonicera japonica, biologie des mauvaises herbes, changement climatique 1. Names Lonicera japonica Thunb. – Japanese honeysuckle (Catling 1997; Nuzzo 1997), Chinese honeysuckle (often referring to var. chinensis), Hall’s honeysuckle (often referring to var. halliana), woodbine (in older textbooks, Nuzzo 1997). Chèvrefeuille du Japon (Erhaeghe 2004), clématite du Japon (USDA 2005), ren dong (Chinese, USDA 2005), nindo (Japanese, USDA 2005), suikazura (Japanese, USDA 2005), madreselva (Spanish, USDA 2005), Caprifoliaceae, honeysuckle family, Caprifoliacées. Lonicera japonica Thunb. ex Murray (Systemat Vegetabilium, ed. 14: 216. 1784 - May–June) has priority over Lonicera japonica Thunb. (Flora Japonica 89–90. 1784 - Aug.). Common synonyms include Nintooa japonica (Thun.) Sweet and Caprifolia japonicum (Thunb.) Kuntze. The variety halliana (Dippel) G. Nicholson is a well-known cultivated variety that has escaped in northeastern North America. This and other varieties, including chinensis (P. Watson) Baker, repens (Hort Bogor. ex Seibold) Rehder, and aureo-reticulata (T. Moore) Jacob-McKoy) are treated as synonyms by most authors. The genus name Lonicera commemorates German naturalist Adam Lonitzer (1528–1586). The specific epithet japonica refers to Japan, where it is native. The horticultural variety name halliana refers to Dr. George Hall, who introduced it to the United States in 1862 (Coombes 1991). 423 424 CANADIAN JOURNAL OF PLANT SCIENCE Lonicera japonica is placed in subgenus Chamaecerasus on the basis of twining growth and flowers in axillary pairs (Sax and Kribs 1930). 2. Description and Account of Variation (a) Description – Perennial, semi-evergreen (in Canada) twining and trailing vine (Fig. 1), ascending to 10 m, but in Canada rarely more than 4 m high. Younger stems reddishbrown or light brown and pubescent, becoming woody, hollow, brownish and glabrous with age, and eventually developing a bark that peels off in long strips. Leaves opposite, ovate or oblong, acute or obtuse and apiculate, entire or early leaves more or less lobed, pubescent but becoming glabrous above, relatively thick, 3–8 cm long and 1–3.5 cm wide, with pubescent petioles 0.4–1 cm long. Flowers white, sometimes with some external purple (or red in var. chinensis), becoming yellowish on the second day after opening, 3–4 cm long, glandular-pubescent externally, with a slender tube and with two spreading and recurved lips at the apex, fragrant, produced all summer in axillary pairs on branches 5–15 mm long on young shoots, often crowded at the shoot tips, with calyx glandular-pubescent or smooth, 1–2 mm long, the individual flowers sessile and attached at the summit of a pedicillate ovary 2–3 mm long, subtended by a pair of ovate bracts 1–2 cm long. Stamens 5, attached to and about as long as the corolla. Style about as long as the corolla. Ovary inferior, developing into a globose or oval, black or purple-black, pulpy berry 6–7 mm long (Fig. 2), which matures from September (in Ontario) to November (in southeastern US). Seeds 1–16 (average 6) in each fruit, brown or brownish-black, ovate or oblong, flat, 2–3 mm long, each ca. 3.6 mg. See Fig. 3 for illustration of a seedling. Description from Bailey (1949), Fernald (1950), Schierenbeck (2004) and examination of living and herbarium specimens. The normal chromosome number for L. japonica is 2n = 18. Wang and Wang (2005) provide details on its karyotype. (b) Distinguishing features – Lonicera japonica is easily distinguished from other northeastern North American Lonicera because it is a twining vine with separate leaves and flowers in pairs on axillary peduncles (Fig. 1). Other Lonicera vines are either rare escapes (L. sempervirens L.) or infrequent natives (L. hirsuta Eat. and L. dioica L.) with leaves below the inflorescence encircling the stem and flowers in clusters at the end of branches. (c) Intraspecific variation – The form with yellow-veined leaves, generally referred to as var. aureoreticulata, is a result of infection by honeysuckle yellow vein virus. Lonicera japonica var. chinensis, with purple, mostly glabrous leaves, and red flowers, has also escaped in North America but does not occur north of New Jersey and Pennsylvania (Fernald 1950). Most of the North American plants and those of Canada are referable to var. halliana, which has green leaves and white flowers that turn yellow. The variety repens has green leaves and white flowers with a purple tinge. At least 12 horticultural varieties are known and many of these, such as “elegant creeper”, Hall’s prolific”, “cream cascade”, “mint crist”, “Interold Darts World” (the latter with purple-crimson flowers), are widely available. Schierenbeck et al. (1995) compared allozyme variability of L. japonica with sympatric L. sempervirens L. in the southeastern United States. Among 10 populations in South Carolina and Georgia, L. japonica had 75% polymorphic loci (Ps), 1.96 alleles per locus (As), 2.28 alleles per polymorphic locus (Aps), and a total genetic diversity (Ht) of 0.216. This variation was consistently lower than L. sempervirens, but genetic variation within both species was equivalent to that of other species with similar life history characters. More recently, Peng et al. (2005) found differing concentrations of two polyphenolic compounds (hyperoside and chlorogenic acid) among samples of L. japonica from three Chinese populations, whereas the concentrations of two others (luteolin and caffeic acid) were similar among populations. 3. Economic Importance (a) Detrimental – Lonicera japonica is considered a problematic invader around the world because it displaces native species and competes with cultivated plants. For example, it is considered a serious threat to the flora of the Juan Fernandez Islands, Chile (Swenson et al. 1997) and to native vegetation in southern Australia (Carr et al. 1992), where it occurs in diverse plant associations including heathlands, sclerophyllous forest, riparian scrub and temperate rainforest. In Hawaii it contributes to the decline of the endangered endemic naenaè, Dubautia latifolia (A. Gray) Keck (Starr et al. 2003). In many parts of the world where it has established, further planting of L. japonica is discouraged and its spread is monitored so that new populations can be rapidly controlled, thus avoiding more expensive control later. More than 50 yr ago, Fernald (1950) described L. japonica in the United States as “a most pernicious and dangerous weed, overwhelming and strangling the native flora and most difficult to eradicate … [it is] extensively planted and encouraged by those who do not value the rapidly destroyed indigenous vegetation (Fernald 1950).” In Michigan, adjacent to its area of occurrence in southwestern Ontario, it has been considered “an aggressive vine that defies eradication, forming dense tangles that overwhelm the native vegetation” (Voss 1996). Lonicera japonica outcompetes native vegetation for both light (Bruner 1967; Thomas 1980) and below-ground resources (Whigham 1984; Dillenburg 1993a, b), and thereby changes the structure of woodlands. Because it is evergreen it has a capacity to photosynthesize and grow during the early spring and late fall (Carter and Teramura 1988a), thereby excluding light from spring ephemerals and other woodland vegetation at these times of maximum light availability. By overtopping pre-existing vegetation, the vines topple shrubs and smaller trees (Slezak 1976; Thomas 1980; McLenmore 1981), producing a more open habitat favourable to their growth. Any disruption of the tree canopy was found to hasten development of L. japonica cover, resulting in further loss of trees (Thomas 1980). Similarly, Webb et al. (2000) found that large-scale removal LARSON ET AL. — LONICERA JAPONICA THUNB. 425 Fig. 1. Flowering branch of Lonicera japonica (modified by P. M. Catling from Fig. 137 on p. 216 in Dippel, L. 1889. Handbuch der Laubholzkinde. Verlag von Paul Parey, Berlin. 449 pp.). of Acer platanoides L. resulted in significant release of nonnative species, including L. japonica. Yurkonis and Meiners (2004) speculated that L. japonica affects local species richness by appropriation of resources available for colonizing species rather than through more direct competitive interactions emphasized in other studies. In southwestern Ontario, L. japonica overgrows and shades native vegetation in a region where numerous species are at risk (Catling and Cayouette 1996). Nonetheless, its potential harmfulness has been recognized only recently. It was not identified in the 1996 national survey of significant invasive species (Haber 1996). In a recent detailed evaluation developed for North America, L. japonica was not among the top 81 invasive species (Catling and Mitrow 2005), but using more updated information it ranked within Canada’s national prioritized list (Catling et al. 2006). 426 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 2. Fruit and seeds of Lonicera japonica. A, Section of a fruiting branch. B, Berries showing position on branch. C, Seeds after removal of pulp. Photos by P. M. Catling from material collected in a ravine at Colchester Harbour, Ontario, on 2006 Oct. 21 by G. E. Waldron. There is much concern that L. japonica establishment after selective logging will prevent forest re-growth (Evans 1984). It is particularly problematic in managed pine stands. For example, Cain (1984) reported that it causes severe regeneration problems in uneven-aged stands of loblolly and shortleaf pines in southeastern Arkansas. Nelson (1953) estimated that 1 million acres in the lower Piedmont had heavy honeysuckle growth, and that perhaps 2.5 million acres had some degree of coverage. The tendency of L. japonica to outcompete tree seedlings following site preparation by discing, burning and bush-hogging led forest companies to conduct research on herbicide control methods (Prine and Starr 1971; McLenmore 1981). Lonicera japonica is also problematic along railway rights-of-way (Regehr and Frey 1988) and in field borders and hedges (Warbach 1953; Gunning 1964). Shankman (1986) found that L. japonica covered abandoned fields shortly after the cessation of cultivation on loess bluffs in western Tennessee, yet it was replaced by continuous forest canopy within three decades. Some caution may be required in using and handling L. japonica for medicinal purposes (see below). There is a single record of three patients incurring a contact dermatitis similar to poison ivy (itchy raised blisters) after pruning Hall’s Japanese honeysuckle (L. japonica halliana), yet it was easily treated with topical steroids (Webster 1993). When eaten in large quantities the fruit may be toxic, causing diarrhea, vomiting, rapid heartbeat, respiratory failure, convulsion and coma (Russell 1997). Lonicera japonica may also act as a host for insect pests of crop plants. In Tift County, Georgia, it was a local host for populations of two noctuid moths, the tobacco budworm [Heliothis virescens (F.)] and the corn earworm [Helicoverpa zea (Boddie)], which feed on crop plants (Pair 1994). The larvae were found in populations along roadsides adjacent to agricultural fields in numerous sites, but whether L. japonica is a host outside of southern Georgia and northern Florida is unknown. Although heliothine larvae were predominately found in crops rather than wild hosts (including L. japonica) during the growing season in Mississippi (Parker 2000), L. japonica could be a significant contributor to over-wintering populations of these larvae (Pair 1994). Similarly, L. japonica may be a winter food source for a tortricid moth in Brazil and Uruguay [Bonagota cranaodes (Meyrick)], thus augmenting its reduction of apple crops (Bentancourt et al. 2004). In North Carolina, L. japonica populations adjacent to crop fields are host to overwintering populations of two spotted spider mite (Tetranychus urticae Koch) that re-invade corn and peanut in the spring (Margolies and Kennedy 1985). Lonicera japonica may also impact agriculture as a source of whitefly-transmitted viruses. For example, whitefly-transmitted begomoviruses have been introduced to Europe with L. japonica (Briddon 2001) and Osaki (1979) noted that a whitefly (Bemisia lonicerae Takahashi) may transmit tobacco leaf curl virus (TLCV) (which attacks tomatoes and tobacco) from L. japonica to crops. (b) Beneficial – Lonicera japonica has long been used in traditional Asian medicine, and related species of Lonicera are used in different parts of China (Bensky and Gamble 1993). The Chinese Pharamacopoeia lists both its stem, Ren Dong Teng or Caulis Lonicerae, and its flowers, Jı̄n Y¯ın Huā or Flos Lonicerae (Tang and Eisenbrand 1992; Bensky and Gamble 1993). Ren Dong Teng is the dry cane of L. japonica collected in the fall and winter; it is used to treat fever, dysentery, abscess and rheumatic swelling. J¯ın Y¯ın Huā is composed of the dry flower buds of L. japonica and other LARSON ET AL. — LONICERA JAPONICA THUNB. Fig. 3. Seedling of Lonicera japonica, 70 d after germination and 105 d after planting. From seed collected at Colchester Harbour, Ontario on 2006 Oct. 15 (specimen voucher at DAO) and grown under unheated greenhouse conditions (+4 to +21°C) through November, December and January (without cold treatment). Drawing by Gerald Waldron. species of Lonicera collected in early summer before blooming (Zhang et al. 2004); it is used to treat abscess, dysentery, cold, and fever, generally acting to “clear heat and poisons” (Bensky and Gamble 1993). Lonicera japonica has been used as an antibacterial, antiinflammatory, antispasmodic, antiviral, depurative, diuretic, febrifuge, and as a cure for tuberculosis, venereal disease and skin disorders (Yeung 1985; Foster and Duke 1998). Lee et al. (1998) noted the general efficacy of L. japonica extracts in the treatment of urinary disorders, fever and headache, and as an anti-inflammatory agent for upper-respiratory tract infections, diabetes mellitus and rheumatoid arthritis. It is an antimicrobial and antiviral agent against 427 influenza and other infectious diseases (Li 1974; Benksy and Gamble 1986). It has also been studied as a source of HIV-1 reverse transcriptase activity, although it has lower efficacy than other Chinese herbs (Chang et al. 1995). Finally, it is a popular, healthy cooling drink among Chinese people during the summer (Li 1974). Lonicera japonica is often combined with other Chinese medicinal herbs for maximum effect (Bensky and Gamble 1993), such as in the popular herbal product Quilinggao (Wong and Chan 2003). Recent studies have confirmed the effectiveness of some traditional uses of L. japonica (for example, Chang and Hsu 1992; Lee et al. 2001; Houghton et al. 1993; Kwak et al. 2003; Kwon et al. 2004), and given its medicinal activity there have been numerous recent attempts to isolate its active ingredients for pharmacological purposes (for example, Tang and Eisenbrand 1992; Peng et al. 2005). Three possible types of contraceptives may be developed from L. japonica: an anti-ovulatory contraceptive, a postcoital contraceptive, and a male contraceptive. The Central Drug Research Institute in Lucknow, India, in collaboration with the US National Institutes of Health, the World Health Organization, and the ICMR have confirmed anti-implantation activity by L. japonica (Chaudhury 1993). Lonicera japonica was first introduced to North America as a garden ornamental. There are numerous early references to its attractiveness (Andrews 1919; Hardt 1986) and it is still popular due to its fragrant flowers and rapid growth (Bradshaw 1991). Lonicera japonica is easily grown and propagated but is not the only choice for the garden. Considering its detrimental aspects, a number of good substitutes have been proposed (Swearingen 2006), including false jasmine [Gelsemium sempervirens (L.) Ait. f.], trumpet honeysuckle (Lonicera sempervirens L.), trumpet creeper [Campsis radicans (L.) Seem. ex Bureau], crossvine (Bignonia capreolata L.), native wisteria [Wisteria frutescens (L.) Poir.], and Jackman clematis (Clematis × jackmanii T. Moore). Numerous studies have considered the benefits of L. japonica as a food for economically important animals. Livestock may feed on it, especially when other roughage is limited, and preliminary experiments showed that it may be acceptable as emergency roughage for dairy cattle (Noland and Morrison 1954). Although the boiled leaves are used as a vegetable and to make a tea, some caution is required because they contain toxic saponins (Facciola 1990). Lonicera japonica has often been recognized as a locally preferred browse species of white-tailed deer, so wildlife managers have recommended transplanting it into old fields and pine groves where deer are desired or even using fertilizers to increase its growth (Handley 1945; Nixon et al. 1970; Sheldon and Causey 1974; Segelquist and Rogers 1975; Stransky 1984; Dyess et al. 1993). With increasing recognition of its invasive properties, however, this is probably ill-advised. In the southeastern US, L. japonica is part of the winter diet of bobwhite quail and turkey (Handley 1945; Brazil 1993). Tangles of L. japonica provide nesting sites, feeding stations, and general cover (Handley 1945), particularly in the 428 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 4. Geographic distribution of naturalized Lonicera japonica in Canada. The herbarium records are based on specimens in DAO, MICH and TRT (acronyms from Holmgren 2005). southeastern US, where leaves are retained through the winter. For example, L. japonica thickets in Ohio were sometimes used over extensive periods for bedding of deer (Nixon et al. 1970). Peles et al. (1995) demonstrated that L. japonica was a preferred nest site and food source of golden mice in Kentucky. Lonicera japonica may also support songbird populations. Suthers et al. (2000) assessed fruit consumption by fall migratory songbirds in central New Jersey and found that fruits of L. japonica were favored. In particular, 54–60% of the diet of neotropical Catharus thrushes feeding in panicled dogwood shrubland was comprised of L. japonica (based on seed recovery from feces). Because the fruits remain on the vines during the winter, they may also be important for overwintering birds (White and Stiles 1992). There have been numerous reports that L. japonica thickets reduce erosion and stabilize river banks (Stadtherr 1982; Evans 1984; Hardt 1986). However, there is little evidence that erosion rates are lower with L. japonica than with other species. Jackson (1974) and Moerman (1998) reported that Cherokee Indians used L. japonica stems to make baskets and trays. This is a recent phenomenon since it escaped from cultivation around 1900. (c) Legislation – Lonicera japonica is not listed as a noxious weed in Canada’s Seeds Act (Agriculture Canada 1985) nor in any provincial weed and seed acts. It is not listed on the United States federal Noxious Weed or Seed lists, but there is control in some states. For example, commercial sale is prohibited in Illinois by the Exotic Weed Act (Nyboer 1990; Nuzzo 1997). Although often recognized as a pest, L. japonica is widely available in the US and Canada and even recommended by some wildlife managers for planting for forage and cover (see Schierenbeck 2004). To assist with the control of L. japonica in North America, its importation, propagation, distribution and sale should be prohibited in Canada. New Zealand has developed legislation that is apparently effective for dealing with invasive species, including L. japonica. The New Zealand National Pest Plant Accord, a cooperative agreement between regional councils and government departments, enables the regional councils to undertake surveillance to prevent the commercial sale and/or distribution of an agreed upon list of pest plants (Biosecurity New Zealand 2001). For example, L. japonica is no longer permitted to be sold, propagated, distributed or commercially displayed because it is on the Regional Surveillance Plant Pest List for Auckland region (Auckland Regional Council 1997). This could provide a model for dealing with invasive species like L. japonica elsewhere. 4. Geographical Distribution Lonicera japonica is native and common in Japan, Korea and eastern China, including Manchuria, where it grows as LARSON ET AL. — LONICERA JAPONICA THUNB. a trailing or climbing vine in thickets on hills and mountainsides (Ohwi 1965; Schweitzer and Larson 1999). It has been introduced and naturalized in temperate and subtropical regions around the world. Currently it occurs in much of southern North America including most of the United States. It is particularly well established in eastern North America north to Missouri, Michigan, southern Ontario, New York and Massachusetts (Hardt 1986; Kartesz and Meachum 1999). It is also established in the Caribbean region, Central and South America, Europe including England, Wales, Portugal and Corsica, northern Africa and South Africa, Australia and New Zealand, the Philippines, the Hawaiian Islands, and the Pacific Islands (Nuzzo 1996; Starr et al. 2003; Schierenbeck 2004). Sasek and Strain (1990) and Evans (1984) provide maps that differentiate areas where it is ornamental, naturalized and invasive. Herbarium specimens documenting the distribution (Fig. 4) of L. japonica are located at CAN, DAO, HAM, TRTE, TRT, UWO and WAT (acronyms from Holmgren 2005). With the exception of two literature reports that are not documented with a specimen (Lockrey and Pegg 1993; Bree 2000), L. japonica is confined in Canada to the Carolinian region of extreme southwestern Ontario, also known as the Lake Erie Lowland ecoregion of the Mixedwood Plain ecozone (Ecological Stratification Working Group 1995). This region is part of the 5b hardiness zone (National Land and Water Information Service 2000), which also extends into much of Nova Scotia and southern British Columbia and therefore L. japonica could occur in these regions. Herbarium and sight records indicate that L. japonica is frequent in parts of mainland Essex County and on Pelee Island (Fig. 4). It also occurs as a cluster of populations in the London area of Middlesex County and in part of the Niagara Peninsula. Single populations are known in Elgin, Kent and Hamilton-Wentworth counties. Sasek and Strain (1990) predicted that a doubling of atmospheric carbon dioxide could allow L. japonica to spread northward up to 400 km. The effects of L. japonica could be exacerbated throughout its range with further global warming, both because of growth enhancement at low temperatures (especially important because it is semi-evergreen and produces leaves in the spring before other species) and greater water use efficiency with increasing CO2. More recent studies at Oak Ridge National Laboratory’s free-air carbon dioxide enrichment (FACE) facility confirmed that L. japonica responds to CO2 enrichment in situ (Belote et al. 2004). 5. Habitat (a) Climatic requirements – Sasek and Strain (1990) concluded that the area in which L. japonica is considered a serious weed is limited by low temperature sensitivity of overwintering stems. The northern limit of this area corresponds to the –20°C isocline of the 30-yr mean lowest winter temperature in the eastern United States. Lonicera japonica is naturalized in regions with more than 100 cm of annual precipitation and mean January temperatures above –1°C (that is, below about 36°N latitude), with growth in New Jersey beginning with temperatures between 1.1 and 429 8.9°C. Cold winter temperatures determine the extent of stem die-back and at their extreme may kill plants (Leatherman 1955). The westward limit of L. japonica in North America relates to insufficient moisture and drought during seedling establishment. These factors limit its naturalization in the western United States to local areas with irrigation, even though it is still a popular ornamental. Lonicera japonica is also limited to warmer and moister parts of its native Japan (Sasek and Strain 1990). Leatherman (1955) noted that the type locality of L. japonica in Japan is climatically similar to eastern North America, consistent with Baker’s (1974) suggestion that climatic similarities may account for the establishment of some weedy species from eastern Asia in parts of eastern North America. (b) Substratum – Lonicera japonica grows best on welldrained soils (Leatherman 1955), but it also occurs in low, wet bottomlands, clay soils with pH from 6 to 7.5, sand plains and mine spoils (Jackson 1974). However, it is noticeably absent on coarse sands and poorer peat soils (Jackson 1974). In the Pennypack Wilderness located in a suburban Pennsylvania landscape, Robertson et al. (1994) found slightly higher frequency and density of L. japonica in mixed mesophytic forest than in mixed oak forest. They suggested that the slightly better drainage, greater acidity, and lower fertility of the latter, because of its origin on sandstone, could be a factor contributing to lower densities. (c) Communities in which the species occurs – Lonicera japonica is found in a variety of habitats, ranging from old fields, thickets, roadsides, fencerows, and open woodlands, to mature woodlands, where it is especially prominent in canopy gaps (Evans 1984), bottomlands (Oosting 1942) and edge habitats (Yates et al. 2004). Lonicera japonica survives in most associations into which it is introduced, except for spruce and fir-dominated communities and coastal pine barrens (Jackson 1974). Webb et al. (2000) reported that L. japonica occurred in forests dominated by either Acer saccharum Marsh., Acer platanoides L. or Fagus grandifolia Ehrh., but densities were much lower in the latter type. Robertson et al. (1994) found L. japonica more frequently in woodlands than in old fields, thickets, mature forests and riparian plots, but density was highest in the thickets and old fields. In North Carolina, L. japonica extended further into forest interior compared with other non-native species and more so on south-facing edges (Fraver 1994). It occurs commonly in old fields that are regenerating to woody vegetation (Keever 1979; Myster and Pickett 1992; Meiners et al. 2001). Near Amherstburg in Essex County, L. japonica occurs on slopes in mature forest dominated by American elm (Ulmus americanus L.), black walnut (Juglans nigra L.), black cherry (Prunus serotina Ehrh.), and green ash (Fraxinus pennsylvanica Marsh). In this area, it was displacing native species of Geum, Parthenocissus, and Circaea and was overgrowing bladdernut shrubs (Staphylea trifolia L.). On Pelee Island in southwestern Ontario, it occurs in the Nature Conservancy’s Shaughnessy Cohen Nature Reserve in moist green ash forest that has developed 430 CANADIAN JOURNAL OF PLANT SCIENCE on previously cultivated land, and in open woodlands dominated by hackberry (Celtis occidentalis L.). At Big Creek in Essex County the plants are widespread in hawthorn (Crataegus spp.) thickets. At several southern Ontario sites, it is climbing over dogwoods (Cornus spp.). In general, the abundance of L. japonica tends to increase with disturbance and edge effects, as with other lianas (Teramura et al. 1991; Merriam 2003; Yates et al. 2004). In mature mixed-oak woodland in New Jersey, Davison and Forman (1982) found a positive correlation between percent cover of L. japonica and light levels. After debris avalanches in Nelson County, Virginia, L. japonica was an important component of vegetative recolonization (Hull and Scott 1982). Since L. japonica may increase light penetration through its effects on vegetation structure and composition, its abundance may be self-perpetuating through positive feedback (Thomas 1980). 6. History Lonicera japonica was introduced in the United States from Japan in 1806 as an ornamental, and was later used for erosion control and highway landscaping (Leatherman 1955). Mack (2003) noted that it had not escaped cultivation by 1860, and there is minimal evidence that it did so before the 1890s because it was not included in floras until 1898 when Britton and Brown reported it as freely escaping from southern New York and Pennsylvania to North Carolina and West Virginia. The first record of escape from cultivation was along the Potomac River in 1882 (Schierenbeck 2004). It was reported as far as Florida in 1903 and Texas in 1918 (Hardt 1986). Leatherman (1955) reported its occurrence in southwest Virginia in 1892, Florida in 1897 and Athens, Georgia in 1900. At the same time that L. japonica was increasing its range as an escape from cultivation in North America it was spreading around the world. For example, it was reported as naturalized in Australia between 1820 and 1840 (Schierenbeck 2004), in New Zealand in 1926 (Williams et al. 2001), and in South America in the 1940s (Schierenbeck 2004). Although the earliest records for adjacent Michigan are 1894 and 1902 (Voss 1996), L. japonica appears to have arrived in Ontario much later. It was reported neither for Ontario by Soper and Heimburger (1982) nor for Canada by Scoggan (1979). Although well established now at Point Pelee and on Pelee Island, it was not reported from these regions during the much earlier surveys of Dodge (1914) and Core (1948), respectively. It was first mentioned in the unpublished reports of Maycock et al. (1976 unpublished, Point Pelee dryland vegetation resource analysis, Point Pelee National Park) and Johnson and Wannick (1977), and then in the published list for Essex County by Botham (1981). The earliest collection that we have seen is from Cedar Creek in Essex County in 1981 (TRTE; for an explanation of this and following acronyms see Holmgren 2005). Considering that the most distinctive plants of the Carolinian region of Ontario were extensively surveyed by Soper and others in the 1940s, 1950s and 1960s, it seems likely that L. japonica established only recently as suggested by the collections. By the early 1990s it was well estab- lished in parts of Essex County and had been found escaped near London in Middlesex County (MICH, TRTE), Port Bruce Provincial Park in Elgin County (Oldham et al. 1993, UWO), and in Kent County (MICH). 7. Growth and Development (a) Morphology – Lonicera japonica is a twiner, a vine whose shoots spirally twine around a support (Carter and Teramura 1988a; Chiu and Ewers 1992). It also produces prostrate shoots that root when they contact the ground and allow lateral spread (Larson 2000). Sasek and Strain (1990) reported that individual stems of L. japonica rarely exceed 2–3 m in length, but extensive vegetative growth and branching allow it to form tangled patches. Teramura et al. (1991) observed that L. japonica consistently maintains its leaf temperatures above ambient by arraying its leaves nearly horizontal, which forms a large absorbing surface. The rate of growth from seedlings is not documented because propagation, particularly of the invasive form, is from stem cuttings. Seedling growth may be slow for the first few years (Little and Somes 1967) and water availability may strongly influence growth rate during this period (Sasek and Strain 1990). Once established, the growth rate may exceed 1.5 m yr–1 (Leatherman 1955), with vines sometimes overtopping 4.5 m trees in a single year (Bruner 1967; Bell et al. 1988), though its success is not attributable simply to high growth rates (see below). Schweitzer and Larson (1999) claimed that the success of L. japonica compared with the native coral honeysuckle (L. sempervirens) might result from greater morphological plasticity. Schierenbeck et al. (1994) demonstrated greater morphological plasticity of L. japonica in terms of compensation to herbivore damage, and Sasek and Strain (1990, 1991) showed greater allocation to leaf biomass with CO2 enhancement. In addition, L. japonica allocates more photosynthetic surface area per unit support tissue than L. sempervirens, leading to greater competitive ability (Sasek and Strain 1991; Teramura et al. 1991; Schierenbeck and Marshall 1993). The stem anatomy of L. japonica may enhance its ability to spread. In a study comparing xylem structure in three Lonicera species with different growth forms, L. japonica was the only one with maximum vessel diameter above 50 µm (Chiu and Ewers 1992). These wide vessels could facilitate long-distance water transport by compensating for its narrow stems. Nonetheless, vessel diameter in L. japonica is at the low end for vines in general, and much lower than cohabitant vines of eastern North America, such as Vitis vulpina L. and Parthenocissus quinquefolia (L.) Planch. These narrow vessels may protect against freezing-induced cavitation and xylem embolism, which facilitates water transport in winter, when the semi-evergreen L. japonica is still photosynthesizing (Bell et al. 1988). (b) Perennation – Lonicera japonica may perennate vegetatively by above ground runners and below ground rhizomes (Larson, Catling and Waldron, personal observation). (c) Physiological data – There have been numerous studies of the role of physiological factors in the spread of L. japon- LARSON ET AL. — LONICERA JAPONICA THUNB. ica. Somewhat surprisingly, its success is attributable neither to high growth rates nor to high photosynthetic rates. Its rate of stem elongation is notably low (Bell et al. 1988; Teramura et al. 1991), and its maximum net photosynthetic rate is similar to non-invasive species (Carter et al. 1989). Teramura et al. (1991), however, showed that light-saturated rates of net photosynthesis are higher in L. japonica than for trees on which it grows. Furthermore, even its new winter leaves in January in South Carolina maintain substantial photosynthetic rates (Schierenbeck and Marshall 1993). Lonicera japonica biomass is positively related to irradiance levels (Leatherman 1955; Thomas 1980; Blair 1982; Baars and Kelly 1996). However, a few studies have shown that L. japonica can survive at low light levels (Blair 1982; Robertson et al. 1994; Baars and Kelly 1996). For example, L. japonica can utilize sunflecks for photosynthesis even if it is unable to effectively climb at low light levels (Carter and Teramura 1988a). Bell et al. (1988) found that L. japonica had a distinctive midday maxima of transpirational water loss compared with morning peaks in Vitis vulpina and Parthenocissus quinquefolia. They concluded that reduced water availability would greatly curtail the activity of the latter species. (d) Phenology – The phenology of L. japonica is likely an important contributor to its weediness (Carter et al. 1989). Its leaves may be evergreen or semi-evergreen depending on location within its range (Evans 1984). In southern Ontario, leaves above the snowline are killed in cold weather, whereas those under the snow are green but flaccid (G. Waldron, personal observation. 2003). In South Carolina, peak leaf expansion occurs in September and again between January and April (Schierenbeck et al. 1994). In southern locations it retains its old leaves through the winter, and they continue to photosynthesize, even as a new leaf cohort begins in January (Schierenbeck and Marshall 1993). The ability to maintain stomatal opening on mild winter days greatly increases its annual carbon budget, especially because maximum conductances on these days may be similar to latespring and summer values (Carter and Teramura 1988b). Schierenbeck and Marshall (1993) estimated that the much higher leaf area and photosynthetic rate of L. japonica in January resulted in five times higher carbon fixation than in L. sempervirens. In the United States, L. japonica exhibits a bimodal flowering period (Pair 1994; Larson et al. 2002). In the southern US, the peak bloom occurs in April and May, and there is a subsequent blooming from September through November (Pair 1994). In central New Jersey, L. japonica fruits ripen in October and persist into the winter (Suthers et al. 2000), and in the southeastern U.S. they are present from September to November. (e) Mycorrhiza – There are no reports of mycorrhizal associations with L. japonica. 8. Reproduction (a) Floral biology – Lonicera japonica is thought to be xenogamous because only 2.1% of flowers from which pol- 431 linators were excluded set fruit (Miyake and Yahara 1998; Larson et al. 2002). Preliminary allozyme analyses support this interpretation (Schierenbeck et al. 1995). Although its flowers have characteristics of the hawkmoth-pollination syndrome (such as long, white tubes; sweet scent; anthers dehiscing at dusk; abundant nectar), bees are prevalent visitors in its native Japanese range (Miyake and Yahara 1998; Miyake et al. 1998), in England (Roberts 1979) and in Arkansas, near the western edge of its North American range (Larson et al. 2002). Miyake et al. (1998) observed visits to L. japonica by three different sphinx moths, an anthophorid and an halictid bee species in Japan. Among the bee and wasp genera listed as pollinators by Schierenbeck (2004) are Bombus, Apis, Vespa and Vespula. Syrphid flies are reported as pollinators by Leatherman (1955) and Schierenbeck et al. (1994). In Arkansas, primary shoots of L. japonica produce paired axillary flowers in early May, and about 3 wk later, after these die, there is a second distinct flowering period, when secondary lateral shoots produce axillary flowers (Larson et al. 2002). Flowering is generally reduced in shaded habitats (Robertson et al. 1994). Individual flowers open and their anthers dehisce in the evening (Roberts 1979; Miyake and Yahara 1998; Larson et al. 2002). In a study conducted within a population in the native Japanese range of L. japonica, the flowers were still white and contained most of their pollen the next morning, but by the end of that day most pollen had been removed and floral color had faded to yellow (Miyake and Yahara 1998). This flowering pattern corresponded with high visitation, but limited pollen removal, by a nocturnal hawkmoth, Theretra japonica de L’Orza, followed by diurnal visits by bee species (Tetralonia nipponensis Pérez and Lasioglossum sp.) that removed most of the pollen from flowers by the end of the day, owing to extensive pollen removal during individual visits. Nocturnal flowering allows long-distance pollination with low pollen removal, followed by higher removal during a diurnal phase of short-distance pollen movement (Miyake and Yahara 1998, 1999). Larson et al. (2002) postulated that pollen delivery limited fertility in Arkansas populations of L. japonica because few floral visitors or ripe fruits were seen, and nectar was observed dripping from the corolla tube. They confirmed pollen limitation by showing that naturally pollinated control flowers set significantly fewer fruit (17.4% of flowers) compared with those to which supplemental pollen was added by hand (78.7%). Fruit set for flowers on secondary shoots (23%) was significantly greater than that on primary shoots (13%). Hawkmoths were only observed on the flowers during the second flowering period, and other insect visitors appeared to be pollen and nectar robbers (see also Roberts 1979), so low visitation rates and low visitor quality accounted for limited fertility. In particular, short distance pollen movement by bees could cause reduced fertility through geitonogamy in the large clones of L. japonica. Pair’s (1994) finding that traps baited with L. japonica flowers were attractive to a number of economically important adult Lepidoptera inspired two studies. Schlotzhauer et al. (1996) reported that constituents derived from phenyl- 432 CANADIAN JOURNAL OF PLANT SCIENCE propanoid increased at night, whereas compounds from lipoxygenase activity increased during the day. Some constituents were constant through the day, whereas others, particularly the dominant terpenoids, peaked in fresh and 24-h-old flowers. Miyake et al. (1998) found that linalool, an isoprenoid, was the most prevalent volatile emitted by flowers of L. japonica. This volatile showed maximal emission during the night, when sphinx moths are active. (b) Seed production and dispersal – Fruit set takes place about 60 d after abscission of the corolla (Schierenbeck 2004). In New Zealand, L. japonica fruits had a mean diameter of 5.1 mm and contained an average of 6.1 seeds that weighed 1.10 mg each (Williams et al. 2001). Lonicera japonica fruits in Arkansas had a mean weight of 186 mg (wet) and 57 mg (dry), with 6.2 seeds per fruit that weighed an average of 3.4 mg (air dried) (Shelton and Cain 2002). The mean seed length within Kentucky populations was 2.89 mm (Hidayati et al. 2000). Most plants from Point Pelee, Ontario had 6 seeds/fruit (G. Waldron, personal observation). Lonicera japonica fruits have been classified as “juicy fibrous,” based on a pulp water content of 80–85% (Williams et al. 2000). Peles et al. (1995) reported a mean caloric content of 4.48 kcal g–1 dry weight, a mean percent crude protein of 9.75%, and total phenolics (percent gallic acid equivalents) of 2.20%. The caloric and crude protein values were within the range normally required by mammalian herbivores, and the phenolic content was considered relatively low. Suthers et al. (2000) reported that their fruit were 1.6% lipid and 50.3% carbohydrate. Handley (1945) recorded 10.42% crude protein, 7.86% fat, and 6.65% crude fiber. White and Stiles (1992) considered the fruit pulp to be of low quality, since it contained less than 10% dry mass lipid. Birds and small mammals have often been listed as dispersal agents for L. japonica (White and Stiles 1992; Suthers et al. 2000). Birds that have been observed to eat the fruits in North America include wild turkey, bobwhite, mockingbird, white-throated sparrow, white-crowned sparrow, dark-eyed junco, American robin, purple finch, goldfinch, bluebird, pine grosbeak, hermit thrush and house finch (Martin et al. 1951; Handley 1945; Schierenbeck 2004). Dispersal may also result from transport and dumping of garden waste, which may include both vegetative material that roots readily as well as seeds (Larson, Catling and Waldron, personal observation). (c) Seed banks, seed viability and germination – Hidayati et al. (2000) found that seeds of L. japonica from Kentucky had underdeveloped spatulate embryos that were about 43% of seed length when dispersed. Embryo length increased very slowly with cold stratification (5°C) in the light, but more quickly with warm stratification (25/15°C). After 12 wk of warm stratification, embryo length had increased about 67%, allowing the embryos to split their seed coats. Waldron collected L. japonica seeds from Point Pelee, Ontario on 20 January, and obtained 50% germination (per- sonal observation). This is the first observation of germination of L. japonica seed in Canada. Hidayati et al. (2000) showed that maximum germination occurs after cold stratification. These results are consistent with earlier studies that concluded that moist L. japonica seeds germinate after 28–40 days stratification at 4°C (Leatherman 1955; Williams et al. 2000). Gibberellic acid (GA3) treatment is a successful substitute for cold stratification (Hidayati et al. 2000). The requirements for embryo growth and dormancy break in L. japonica correspond to germination phenology under natural conditions (Hidayati et al. 2000). In Kentucky, seeds began to germinate under leaf litter beginning in late January 1998, but peak germination was between February 15 and 22. Since most seeds of L. japonica dispersed in the fall are not exposed to warm temperatures before germination, only cold stratification is required for germination. Physiological dormancy is broken in mid-winter, but embryos do not grow until temperature increases later in the season. There is limited potential for a persistent L. japonica seed bank since seeds germinate to high percentages under either leaf litter or soil (Hidayati et al. 2000; Fowler and Larson 2004). Shelton and Cain (2002) found that seed viability was significantly reduced after 2 or 3 yr in the forest floor, with only 1% of seeds germinating after 3 yr of field storage. (d) Vegetative reproduction – Once it colonizes a site, L. japonica spreads extensively by vegetative means (Slezak 1976), including rhizomes and prostrate shoots. Larson (2000) compared circumnutation (rotation about a central axis) behavior in L. japonica and L. sempervirens. She found that erect shoots behaved quite similarly (rotating about 31° clockwise per hour), but that their prostrate shoots differed markedly. Shoots of L. japonica had reduced circumnutation (averaging 2.1° per hour) compared with those of L. sempervirens. This behavior increased the rooting success and dispersion of L. japonica, because its prostrate shoots grow in a relatively constant compass direction compared with the more erratic growth (because of interference with the ground) of L. sempervirens shoots. Consequently, the maximum dispersion of L. japonica prostrate shoots was 39% greater than that of L. sempervirens, despite similar total shoot lengths. Furthermore, shoots of L. japonica remained closer to the ground, which resulted in much greater node rooting. All nodes of L. japonica that were less than 2 cm above the ground developed roots. Effectively, the lateral shoots of L. japonica give them a behavior much like the stolons of clonal herbs, and this clonal mobility, combined with its climbing success, allow it to exploit varied microclimates (Larson 2000). 9. Hybrids Hybrids are only known between species of the same section of Lonicera (Sax and Kribs 1930). Sax and Kribs (1930) assign L. japonica to subgenus Chamaecerasus, section Nintooa, with Chinese species such as L. henryi Hemsl. and L. alseuosmoides Graebn. Other species of section LARSON ET AL. — LONICERA JAPONICA THUNB. Nintooa are not established in North America. Chiu (1998) suggested that the variability in L. japonica in Taiwan could be related to the presence of hybrids and that L. shintenensis Hayata may be a hybrid of L. japonica and L. hypoglauca Miq. 10. Population Dynamics Thomas (1980) hypothesized the following sequence of events in L. japonica colonization of a forest on Theodore Roosevelt Island (on the Potomac River in Washington, DC). First, he found reduced vertical structure in habitats with L. japonica, suggesting that disturbance of this structure allows it to colonize. It may be present in the understory for long periods even in closed-canopy forest (Whigham 1984; Robertson et al. 1994; Spyreas et al. 2004), but can respond rapidly to disturbance (Leatherman 1955; Slezak 1976; Davison and Forman 1982; Carter and Teramura 1988a; Teramura et al. 1991). The second major colonization event hypothesized by Thomas (1980) was that extensive growth of L. japonica in response to greater light effectively allows it to form a new ground layer, which may suppress the reproduction of overstory dominants and kill small trees and shrubs. The rapid development of populations of L. japonica may also result from its allelopathic effects on trees (Skulman et al. 2004) and herbs (Thomas 1980; Friedland and Smith 1982; Davison and Forman 1982). Suppression of dominant species may lead to positive feedback that converts the forest to an open vine-dominated disclimax (Little 1961; Thomas 1980; Whigham 1984). However, on Theodore Roosevelt Island, L. japonica is gradually being replaced by the invasive alien Hedera helix L. and is expected to decline with time (Thomas 1980). Lonicera japonica and Liquidambar styraciflua L. have been studied as a model system for the effect of vines on tree growth. Whigham (1984) found that the growth rate of the trees was significantly higher when vines were removed from both the tree and the ground. This study suggested that an understory of vines alone can suppress the growth of canopy trees, likely as a result of root competition for nutrients and water. Similarly, Dillenberg et al. (1993a) showed that below-ground competition with L. japonica significantly decreased Liquidambar styraciflua sapling growth, and that canopy competition was only effective when it occurred in concert with root competition. Meiners et al. (2001) found that L. japonica colonized fields within 5 yr of abandonment and reached its peak after 15 yr, whereas Myster and Pickett (1992) suggested a somewhat later peak. 11. Response to Herbicides and Other Chemicals Evans (1984) reviewed early studies of herbicide treatments on L. japonica and Nuzzo (1997) provided a later update. Glyphosate (Round-up) treatment is often recommended, though L. japonica may be defoliated by high-volume spring sprays of a variety of herbicides (Evans 1984). However, control is not dependable, and some individuals are nearly always present after treatment (Warbach 1953; Little 1961). Nyboer (1990) pointed out that the semi-evergreen habit of L. japonica allows it to be detected and treat- 433 ed in the winter when co-habitants are dormant (see also Nuzzo 1997). He recommended careful application of glyphosate or Crossbow (triclopyr and 2,4-D combination) at this time of the year, but the latter may be more persistent. Note, however, that Regehr and Frey (1988) reported that applications of glyphosate or dichlorprop plus 2,4-D were less effective when the leaves were senescing in December. Cain (1984) found that hexazinone (Velpar L) was more effective than amitrol (Amitrol T) or mechanical cutting over a 3-yr study in all-aged loblolly-shortleaf pine stands in Arkansas, but the trees had to be protected from the application and multiple applications were required. Yeiser and Howell (1997) reported that metsulfuron (Escort) and glyphosate (Accord) provided the best control in young clearcuts and in older bottomland hardwood stands. Caiazza and Quinn (1980) found that lower leaf surface stomatal density decreased and upper surface trichome density increased in L. japonica populations closer to a zinc ore smelter in Pennsylvania. They suggested that lowered stomatal density could reduce the penetration of gaseous particulates into the mesophyll (e.g., along a gradient of SO2 air pollution), whereas increasing trichome density could lower metabolic rates and thereby reduce pollution damage. 12. Response to Other Human Manipulations In a recent review, Schierenbeck (2004) noted that “although L. japonica is naturalized in many areas where it has been introduced, there still may be hope for the control of local infestations and of its further spread in areas that have a fairly recent introduction history.” This obviously applies to Canada. A number of mechanical methods are available, some to be used in combination with chemical methods. Hand-pulling is effective only for removing L. japonica seedlings, as older plants have extensive roots that will regenerate (Nuzzo 1997). Consequently, some managers have considered hand-pulling only practical for small areas to remove incipient patches of seedlings. Hand-pulling can reduce spraying requirements, however, and in some cases has been used to remove L. japonica over hundreds of acres. The roots are pulled out and tied up, but the plants are not removed from the trees since this would simply provide light for regrowth (M. Imray, personal communication). Mowing and grazing may reduce the spread of vegetative runners (Handley 1945; Nelson 1953), but tend to increase the number of stems or produce a low mat (Stransky 1984; Faulkner et al. 1989; Nyboer 1990). Repeated mows may reduce recovery (Evans 1984). The efficacy of grazing has not been shown empirically, and its costs likely outweigh its benefits in many sensitive habitats (Evans 1984). Unless it is repeated, grazing may simply stimulate resprouting, as with mowing. Bush-hogging is ineffective since re-invasion occurs within a year (McLenmore 1985). Discing has proven to be effective, but it destroys native species and may stimulate germination of L. japonica seedlings (Nuzzo 1997). Lonicera japonica is susceptible to fire (Handley 1945), but resprouts from its roots after a single burn (Leatherman 1955; Faulkner et al. 1989). Pre-burn cover is re-established 434 CANADIAN JOURNAL OF PLANT SCIENCE within a few years (Oosting and Livingstone 1964; Barden and Mathews 1980). Burning may be most effective combined with foliar application of reduced amounts of herbicide, such as glyphosate (Nyboer 1992; Nuzzo 1997). Mid-summer cutting or fall grazing may also limit resprouting (Evans 1984). Stransky (1984) studied alternate control methods within deer food lots and reported that burning is an inexpensive way to confine honeysuckle to food plots. Lonicera japonica may be a candidate for biocontrol (see below), especially given that it has no close relatives in North America, but this requires the usual cautions about potential unintended consequences of such action. 13. Response to Herbivory, Disease and Higher Plant Parasites Lonicera japonica is sometimes described as “pest-free” (Dehgan 1998), and the absence of herbivory in North America has been used to explain its success (Leatherman 1955). Dillenberg et al. (1993b) noted that L. japonica had much less leaf damage due to mildew and beetle grazing than Parthenocissus quinquefolia. However, in young woodland in South Carolina, Schierenbeck et al. (1994) found that L. japonica was more subject to herbivory than L. sempervirens. When subjected to insect and mammal herbivory, L. japonica showed a compensatory response that led to its greatest biomass and allocation to leaves. In contrast, L. sempervirens showed the opposite pattern, accumulating the most biomass in the absence of herbivory. In short, the ability of L. japonica to compensate for relatively low rates of herbivory gave it an additional advantage over its congener, as well as other species. The early season leaf growth of L. japonica also allows it to better escape herbivory before insect herbivores are active. Herbivory (a) Mammals, including both domestic and wild animals – Livestock feed on L. japonica, especially when other roughage is limited (Noland and Morrison), and their feeding stimulates sprouting. Williams and Timmins (1997) reported a rapid response to its browsing by goats, deer and opossums. Lonicera japonica is a locally preferred species of white-tailed deer (Handley 1945; Stransky 1984). (b) Birds and/or other vertebrates – Consumption of fruit by birds is beneficial for the dispersal of L. japonica seeds and the foliage is consumed by bobwhite quail and turkey during the winter, but it is a minor part of their diet (Handley 1945). No records of consumption by other vertebrates have been found. (c) Insects – In China, L. japonica is host to aphids and a cicadellid [Empoasca biguttula (Ishida)] that are also pests of cotton (Chen et al. 1987; Li and Wen 1988). The cerambycid Xylotrechus grayi White also feeds on L. japonica in its native range. In North America, L. japonica is affected by leaf rollers and scale insects (Brickell and Zuk 1997), noctuid moths (Pair 1994), and tortricid moths (Bentancourt et al. 2004). (d) Nematodes and/or other non-vertebrates – In North Carolina, two spotted spider mite (Tetranychus urticae) occurs on L. japonica (Margolies and Kennedy 1985). Diseases (a) Fungi – Lonicera japonica is sometimes damaged by powdery mildew, leaf spots and blights (Brickell and Zuk 1997). Some but not all populations are resistant to leaf blight caused by Insolibasidium deformans (C.J. Gould) Oberwinkler and Bandoni (Gould 1945). (b) Bacteria – No record has been found. (c) Viruses – Brunt et al. (1980) isolated a previously undescribed carlavirus, honeysuckle latent virus, from plants in southern England that had severe leaf chlorosis. Macintosh et al. (1992) used monoclonal antibodies to confirm the presence of whitefly-transmitted tobacco leaf curl virus in two European populations of L. japonica var. aureo-reticulata. This geminivirus could be spread from the ornamental L. japonica by whiteflies, potentially infecting European crops (Osaki 1979). Also, honeysuckle yellow vein mosaic begomovirus has been reported from Japanese and New Zealand populations of L. japonica (Lyttle and Guy 2004; Were et al. 2005). 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