HORTSCIENCE 53(9):1244–1249. 2018. https://doi.org/10.21273/HORTSCI13112-18 Native Weedy Pests of the Deep South S. Christopher Marble1 Department of Environmental Horticulture, University of Florida, Mid-Florida Research and Education Center, 2725 South Binion Road, Apopka, FL 32703 Additional index words. invasive plants, nursery crops, landscapes, environmental horticulture Abstract. By definition, an invasive plant is a non-native or alien species whose introduction causes or may cause economical or environmental harm. Due to well-documented and widespread devastating impacts of invasive plants, all exotic or introduced plant species often are erroneously referred to as invasive or considered detrimental, whereas native plants may be promoted as beneficial. Although invasive plants have been the subject of a great deal of research and discussion, less attention has been placed on native plant species that can become economically important weedy pests under certain scenarios, such as in landscape plantings or agricultural production systems. The objective of this manuscript is to synthesize current literature available on native weedy plants in Florida and other Southern United States (including Alabama, Arkansas, Georgia, Louisiana, North Carolina, Mississippi, South Carolina, Tennessee, and Texas) and discuss how their biology paired with human activities, preferences, and available management practices cause these species to proliferate and be problematic. Focus is placed on nine important native weeds in residential and commercial landscape plantings, including spurges (Euphorbia spp.), woodsorrels (Oxalis spp.), saw palmetto [Serenoa repens (Bartram) Small], bracken fern [Pteridium aquilinum (L.) Kuhn], artillery weed (Pilea microphylla L.), Virginia creeper [Parthenocissus quinquefolia (L.) Planch], trumpet creeper [Campsis radicans (L.) Seem. Ex Bureau], eastern poison ivy [Toxicodendron radicans (L.) Kuntze], and pennyworts/dollarweed (Hydrocotyle spp.). Reasons these species become problematic, including fast growth and reproductive rates, lack of selective management options, and ability to thrive in the landscape environment, also are discussed.
An invasive species is defined as ‘‘an alien et al., 1992). Many authors generally refer to to hybridization and other factors (Ayres (non-native) species whose introduction does weeds as problematic plants in managed et al., 2004). The objective of this manuscript or is likely to cause economic or environ- sites, such as agriculture, whereas ‘‘inva- is to provide a concise description of about mental harm or harm to human health’’ sives’’ are non-native plants growing aggres- nine native weed pests in the southeastern (USDA, 2018a). Invasive plants have been sively or expanding in nonmanaged areas United States, with specific focus on species subject to significant research from environ- (Ellstrand, 2009; Radosevich et al., 2007). that cause management issues or losses in mental (Pimentel et al., 2005), economical Alternatively, Rejmanek (2000) defined in- ornamental landscapes and provide reasons (Lovell et al., 2006; Olson, 2006), and man- vasive taxa as a subset of naturalized taxa that why these native species become problematic agement points of view (Kettenring and are non-native and form sustainable popula- (Table 1). Adams, 2011). About 25,000 alien plant tions without direct human help but not species have been introduced into the United necessarily spreading. The general public COMMONALITIES OF NATIVE AND States. Pysek (1995) defined an alien species may consider all exotic or weed plants as INTRODUCED WEEDS as ‘‘one which reached the area as a conse- invasive, regardless of their native status, quence of man or his domestic animals.’’ making consistent terminology very impor- Generally, a weed is a plant (native or Although some are very profitable agricul- tant when discussing different categories of non-native) that is not valued where it is tural crops [e.g., Zea mays L. (corn), Triticum species to avoid confusion (Caplat and growing (USDA, 2018b). Regardless of na- spp. (wheat), Oryza sativa L. (rice)], many Coutts, 2011). There is considerable debate tive status, traits of all weedy plants (Mack, cause significant environmental harm, result- about defining an invasive (Colautti and 1996; Olson, 1999), most notably by Baker ing in losses of $35 billion annually MacIsaac, 2004) or native species (Kendle (1974) include 1) ability to germinate in (Pimentel et al., 2005). Due to the overall and Rose, 2000; Webb, 1985), as not all different environments, 2) longevity of seed, damage associated with invasive plants, more species can be clearly categorized. Discus- 3) rapid growth, 4) continuous seed produc- attention has been placed on invasive (i.e., sing the complex issues that lead to these tion, 5) self-compatibility, 6) ability to cross exotic or non-native) weeds and their im- categorizations such as time, human interac- pollinate, 7) prolific seed production, 8) high pacts. Although invasive plant species result tion, or geopolitical boundaries are beyond plasticity, 9) short- and long-distance seed in significant losses, native plants also may the scope of this manuscript but have been dispersal mechanisms, 10) vigorous vegeta- cause management issues by spreading ag- summarized in Kendle and Rose (2000). tive reproduction for perennial species, 11) not gressively in natural or managed systems, It is common for authors to report native easily pulled from the ground, and 12) having such as commercial or residential landscapes status differently for many species. To estab- a special competitive advantage (e.g., allelo- managed for aesthetic appeal. lish a delineation between native or exotic chemicals). Several comprehensive quantita- Terms such as ‘‘invasive’’ or ‘‘exotic’’ are plants, the U.S. Department of Agriculture tive analysis of various weed species lists have sometimes used synonymously by the lay- (USDA)–National Resources Conservation been conducted to identify plant traits that person, and there is disagreement within Service database (USDA-NRCS, 2018) was may lead to ‘‘weediness.’’ Kuester et al. academia in defining an invasive species used here to classify species as native or (2014) analyzed plants from the USDA plants and the difference in invasive plants vs. introduced. Of the 357 weeds listed in the database and the Weed Science Society of weeds (Davis and Thompson, 2001; Perrins USDA Weeds of the U.S. list (USDA, America (WSSA) composite list of weeds 2018b), 173 (48%) are categorized as native (Van Wychen, 2016) to test for significant or likely native. However, native status often differences between weeds and nonweeds is defined by geopolitical boundaries (such as using both native and introduced species by This paper results from the workshop entitled ‘‘Strategies for mitigating invasiveness of native the contiguous 48 states) and may not in- examining traits, such as herbicide resistance, species,’’ held 20 Sept. 2017 at the ASHS Confer- dicate true native range, such as Spartina environmental stress tolerance, growth and ence, Kona, Hawaii, and sponsored by the Invasive alterniflora Loisel. (smooth cordgrass), reproductive rates, life cycle, genome size, Plants Professional Interest Group (INPR). which is native to the southeastern United and introduction date. Of the 12 traits evalu- 1Corresponding author. E-mail: marblesc@ufl.edu. States but invasive in parts of California due ated, four (annual life form, high growth rate,
1244 HORTSCIENCE VOL. 53(9) SEPTEMBER 2018 WORKSHOP
Table 1. List of common native plants that become weeds in southern landscapes in the United States. Genus and species Common name Native rangez Acer rubrum Red maple Eastern United States, FL west to TX, north to Canada Campsis radicans Trumpet creeper Throughout most of contiguous United States Conyza canadensis Horseweed Throughout the United States and Canada Cyperus surinamensis Surinam sedge FL west to TX, north to NE Euphorbia maculata Spotted spurge Throughout contiguous United States Hydrocotyle umbellata Pennywort/dollarweed Throughout Southeastern United States, CA and OR also listed Oxalis corniculata Creeping woodsorrel Throughout contiguous United States Oxalis stricta Yellow woodsorrel Most of contiguous United States, CA, OR, NV, UT not included Parietaria floridana Florida pellitory Southeastern United States, FL west to TX, north to NC Parthenocissus quinquefolia Virginia creeper Eastern United States, FL west to TX, north to Canada Paspalum setaceum Thin paspalum Throughout most of contiguous United States Pilea microphylla Artillery weed FL and southern portions of AL, AR, GA, LA, MS, TX Pteridium aquilinum Bracken fern Throughout contiguous United States Richardia scabra Rough mexican clover Southeastern United States, FL west to TX, north to VA Serenoa repens Saw palmetto FL, TX, southern portions of AL, GA, LA, MS, SC Sida acuta Common sida FL north to AL, west to TX Toxicodendron radicans Eastern poison ivy Throughout eastern United States, east of TX, north to Canada zNative status and range derived from USDA Plants Database (USDA-NRCS, 2018). FL = Florida; TX = Texas; NE = Northeast; CA = California; OR = Oregon; NV = Nevada; UT = Utah; NC = North Carolina; AL = Alabama; AR = Arkansas; GA = Georgia; LA = Louisiana; MS = Mississippi; VA = Virginia; SC = South Carolina. high fruit abundance, and high seedling vigor) before human settlement. However, fire sup- NATIVE INVADERS OF LANDSCAPES were more likely to be associated with weedy pression by people, livestock overgrazing plants compared with nonweedy plants re- prairie grasses that previously outcompeted Many of the most common classical gardless of introduction status, and these traits eastern redcedar, and other factors have led to landscape weeds are native, such as Hydro- were more likely to occur among introduced this species becoming a troublesome weed in cotyle spp. (pennyworts), some species of weeds compared with native weeds. The Oklahoma and other states (Ansley and Digitaria (crabgrasses), specifically D. cilia- authors also found that although introduced Rasmussen, 2005). ris (southern crabgrass), Gamochaeta pur- weeds were more likely to be salt tolerant, they Most research of plant invasions has purea (L.), Cabrera (purple cudweed), and were less likely to be shade and calcium focused on very large ecological scales at several Oxalis spp. (woodsorrel) (Neal et al., carbonate tolerant, indicating that native and a national or regional level (Lonsdale, 1999). 2017). In the 2015 WSSA survey of most introduced weeds may have different stress In these nonmanaged areas, genetic traits common and troublesome weeds in land- adaptations. In addition, 73% of herbicide- would likely be the primary means by which scapes (Van Wychen, 2016) (including sur- resistant species in the U.S. flora were in- one species could outcompete another, and vey results from ornamentals not classified troduced weeds, and these species were more eventually become established/naturalized, as in a production system), 50% are classi- likely to rapidly reproduce a high number and then possibly invasive. In managed fied by the USDA Plants database as native. offspring. Sutherland (2004) performed landscapes, weedy traits common to both Of the southern states that participated in a similar analysis and found that although introduced and native weeds (Kuester et al., the survey (Arkansas, Florida, Mississippi, certain traits such as generalized pollina- 2014; Sutherland, 2004) would still likely be North Carolina, Texas, and Virginia) the tion, short regeneration time, competitive required. However, some traits may not be as most frequently listed native species were growth, or protection from herbivory such critical due to very high levels of routine and Euphorbia spp. (syn. Chamaesyce)(spurges) as being armored (spines or thorns) distin- continual human activity that may provide (Van Wychen, 2016), whereas the most guished weeds from nonweeds, these traits additional opportunities for weeds to be- frequently introduced weed listed was Cyn- were common among both native and non- come aggressive or outcompete landscape odon dactylon (L.) Pers. (bermudagrass). native weeds. Plants frequently perform plants due to inputs associated with plants Of the 30 plant species, 15 were introduced better and are less affected by herbivores grown for aesthetic purposes (e.g., irriga- and 12 were native. Three species could be in an introduced range (Bossdorf et al., tion, fertilization, insecticides and fungi- considered either native or introduced as 2005). It is often assumed that exotic weeds cides, etc.). some survey participants listed genera [e.g., are more aggressive than native weeds. Another important distinction is the Cardamine, which has introduced (C. hirsuta) However, some authors have stated that threshold in which these common or trou- and native (C. pennsylvanica) species] when traits commonly associated with invasive blesome species are considered a nuisance several species may be considered common plants are shared with many successful and or problematic. In natural or nonmanaged or troublesome (Table 2). expanding native species (Thompson and sites, plant species are of specific con- In the southern United States, some of Davis, 2011; Thompson et al., 1995). Re- cern when they begin to alter native plant these native weeds can be especially prob- search by Kuester et al. (2014) and Suther- communities and ecological processes lematic. Certain native species become weedy land (2004) also show that the same traits (Villa et al., 2011). Weeds, whether native pests due to high seed production, fast growth make invasive and native weeds successful. or introduced, require action in food crops rate, or ability to tolerate a wide range of When native plants become weeds, it is or other agricultural production systems environmental conditions, but management often due to human-induced disturbances when populations reach levels where yield practices also play a role (Sutherland, 2004). such as agriculture, construction, or recrea- is negatively impacted (Cousens, 1985). If any unwanted plant can be considered a tion that creates vegetation gaps (Baker, In landscapes managed for aesthetic pur- weed, any plant species could be considered 1962; Thompson et al., 1995). A classic poses, pest thresholds can be extremely low- a weed depending on the situation. However, example of a native species aggressively based, depending on personal preferences for a species to receive attention (e.g., re- spreading throughout its native range due to and expectations (Raupp et al., 1988). Even search to develop management guidelines, human disturbance is Juniperus virginiana L. when weed populations do not reach levels inclusion in identification guides, bulletins, (eastern redcedar) and other Juniperus spe- that affect landscape plants negatively, they and other resources, etc.), it typically must cies that were once confined to specific areas may still be considered a nuisance due to cause considerable management issues (aes- due to frequent fires that occurred in the their appearance in a highly manicured thetic or otherwise) on a local, regional, grasslands in the Midwestern United States landscape. or national level. By reviewing common
HORTSCIENCE VOL. 53(9) SEPTEMBER 2018 1245 Table 2. Native weedsz listed as common or troublesome in landscapes and ornamentals in the 2015 Weed of herbicides (Marble et al., 2017). Spurge Science Society of America weed survey.y and oxalis are by no means the only two States citing as common/troublesome common native weed species that pose Genera and speciesx Common name Common Troublesome challenges due to rapid growth and re- Cardamine spp. Bittercress species FL productive rates, although they are very Cyperus compressus Annual sedge MS prevalent. Other common weed species that Eclipta prostrata Eclipta FL FL thrive in landscapes for these reasons include Euphorbia humistrata Prostrate spurge AR, MS, TX MS Acer rubrum L. (red maple), Parietaria flor- Euphorbia maculata Spotted spurge VA idana Nutt. (florida pellitory), and Richardia Euphorbia spp. Spurge species FL, NC FL scabra L. (rough mexican clover), among Ipomoea spp. Morningglory species NC others. Oxalis corniculata Creeping woodsorrel VA Oxalis spp. Woodsorrel species FL Oxalis stricta Yellow woodsorrel FL, AR, MS NATIVES LACKING EFFECTIVE OR Richardia spp. Mexican clover species FL SELECTIVE MANAGEMENT Rubus trivialis Southern dewberry TX OPTIONS Sibara virginica Virginia winged rockcress MS Stachys floridana Florida betony MS Many native weeds are troublesome be- Toxicodendron radicans Eastern poison ivy NC, TX cause of the lack of effective management zNative status was based on USDA Plants Database (USDA-NRCS, 2018). options, such as Serenoa repens (Bartram) y Responses used included those from southern U.S. states (AR, FL, MS, NC, TX, and VA) and included Small (saw palmetto) in Florida. Saw pal- common or troublesome weeds in landscapes or in ornamentals not specified as being production metto can grow up to 2.5 to 3.5 m tall and has ornamentals (i.e., in container or field production). Full survey results are available in Van Wychen (2016). a clumping growth habit that requires ample xSurvey respondents may have included only genera when multiple species from that genera are common or troublesome in landscapes. Those genera may include both native and introduced species. space not available in smaller landscapes. As FL = Florida; MS = Mississippi; AR = Arkansas; TX = Texas; VA = Virginia; NC = North Carolina. the result of a deep root system, it is difficult to remove or transplant. Often the plants can become weedy in pastures, reducing forage yield, or can prevent access to power poles or landscape weeds that are included in man- 2002; Marble et al., 2009; Norcini and other utilities. Although it is very slow- agement or identification guides, it could Aldrich, 1992; Stamps and Neal, 1990), but growing, saw palmetto is very difficult to be deduced that native weeds become prob- spurge continues to be one of the most control. Some herbicides are effective (Fast lematic most commonly due to 1) fast growth common landscape weeds (Neal and Derr, et al., 2015), but most products found to be and reproductive rates, 2) lack of effective or 2005: Neal et al., 2017). effective are not labeled for use in residential selective management options, or 3) ability to Despite susceptibility to most preemer- or commercial landscapes (Fast et al., 2015; thrive in the landscape environment, espe- gence herbicides, several Oxalis spp. also are Shiver et al., 1991). cially when where proper cultural practices problematic weeds in landscapes and in the Pteridium aquilinum (L.) Kuhn (bracken are not followed. southern United States (Neal et al., 2017). fern) is a species with several varieties native The most common species encountered in to North America and distributed all over the NUISANCE NATIVES DUE TO FAST southern landscapes is O. stricta or O. corni- world (Page, 1976). In areas that are dis- GROWTH AND REPRODUCTION culata. Both species are perennial and be- turbed due to deforestation or agriculture and come troublesome because of their ability to in landscapes, the species has a tendency to Many weed species have the ability to spread via seeds and vegetatively through spread out of control and produce mono- reproduce and spread quickly (Kuester et al., rhizomes and stolons (Marshall, 1987; Neal cultures that prevent regeneration of other 2014). The genera Oxalis (woodsorrel) and and Derr, 2005). Stevens (1932) reported that plants. Schneider (2006) reported that over Euphorbia (spurge) contain several native O. stricta produces 570 seeds per plant, but the span of 15 years, areas occupied by species routinely identified as problematic because of its perennial nature seed production bracken fern monocultures increased 4-fold in landscapes. could occur at almost any time of the year in the Calakmul region in Mexico. In addition Many spurge species are widespread depending on the environment (Marshall, to aggressive growth, bracken fern are poi- throughout the United States (Dunn, 1979). 1987). Both species also produce seed cap- sonous and a concern for grazing livestock Spurges are well controlled by many pre- and sules that explosively dehisce on maturation, (Knight and Walter, 2001). Multiple herbi- postemergence herbicides labeled for use in spreading seeds up to 2 m away from the cides and other control measures have been landscapes (Neal et al., 2017); however, these mother plant (Van Der Pijl, 1969). Seeds of O. evaluated on bracken fern in many parts of species, particularly E. maculata (spotted stricta and O. corniculata have no dormancy the world (Lawton, 1988; Milligan et al., spurge), have management issues due to a fast requirement (Neal and Derr, 2005) and can 2016; Pakeman et al., 2002; Stewart et al., growth rate and high seed production germinate over a broad range of temperatures 2008). Bracken fern is difficult to control (Ehrenfeld, 1976). A single plant may pro- (Holt, 1987). In studies by Holt (1987), fresh with herbicides because few chemicals, such duce several thousand seeds (Molinar, 2009; seeds of O. corniculata showed up to 90% as glyphosate, are translocated in large Suzuki and Ohnishi, 2006). Early studies by germination. enough percentages to affect the rhizome Stevens (1932) showed seed production from Despite effective control by numerous (Gaskin and Kirkwood, 2017). Herbicides common Euphorbia species such as E. nutans herbicides, Euphorbia and Oxalis species including 2,4-D, triclopyr, metsulfuron, and and E. humistrata ranged from 1720 to more are management challenges in landscapes chlorsulfuron often are recommended for than 14,000 per plant. In addition to signif- because of their ability to produce copi- bracken fern control in pastures (Sellers icant seed development, vegetative and re- ous amounts of highly viable seeds, ability et al., 2017), but these herbicides would not productive growth occur simultaneously in to grow in a diverse range of conditions, and be suitable in most landscape situations. spotted spurge resulting in increased repro- in the case of oxalis, ability to spread also Glyphosate is the top-selling pesticide ductive outputs (Suzuki and Ohnishi, 2006). spread vegetatively. Although cultural prac- worldwide (EPA, 2017) and is readily avail- Spotted spurge seed also has no dormancy tices such as mulching also have been shown able to homeowners at retail outlets. Many requirement and can produce multiple gen- to provide effective control of both spurge homeowners do their own pest control, and erations per year (Neal and Derr, 2005; and woodsorrel (Cochran et al., 2009; Wilen glyphosate may be the only herbicide avail- Suzuki and Ohnishi, 2006). Much research et al., 1999), mulch will decompose over able for them to purchase in affordable has been conducted to determine effective time and will not provide long-term control quantities or without a pesticide license. control methods for spurge (Altland et al., without supplemental handweeding or use Pilea microphylla L. (artillery weed) is
1246 HORTSCIENCE VOL. 53(9) SEPTEMBER 2018 a common weed in Florida and in many other NATIVE WEEDS THAT THRIVE IN vulnerable to many invasive or introduced southeastern states that is poorly controlled THE LANDSCAPE ENVIRONMENT weed species {e.g., doveweed [Murdannia with glyphosate. Once widely planted as an nudiflora (L.) Brenan] or hairy crabgrass ornamental groundcover (Blessington and Improper use of fertilizers, irrigation, [Digitaria sanguinalis (L.) Scop.]}, native Collins, 1993), artillery weed spreads aggres- mowing, and other practices can stress turf- plants can become weedy in the artificial sively in landscape planting beds and in grass species and allow certain weed species environment of a residential landscape. cracks in hardscapes. Saha et al. (2017) to proliferate. Homeowners may be unaware reported that glyphosate provides only sup- of proper cultural practices, although 70% to CONCLUSIONS pression of mature artillery weed, with fresh 80% may perform their own lawn/garden weight reductions ranging from 30% to maintenance (Butterfield, 1999; Varlamoff Landscapes are vulnerable to weed in- 50% in one experiment. Numerous preemer- et al., 2001). Studies have shown that many festations in many ways. Many non-native gence herbicides provide effective control, homeowners do not know how much water and native species (such as spurge or wood and herbicides including flumioxazin and they are applying with irrigation systems sorrel) are routinely reintroduced to land- glufosinate provide effective postemergence (Bremer et al., 2012) and may excessively scapes via infested container-grown orna- control (Saha et al., 2017). Although many of irrigate their lawns (Romero and Dukes, mentals. Almost any weed could become these herbicides are available to homeown- 2011), which can increase growth of many problematic in container nursery produc- ers, they are typically only available for weed species. Hydrocotyle spp. (pennyworts, tion due to high levels of fertilization and purchase in very large quantities (e.g., 9.5-L dollarweed) are native to the southeastern irrigation (Stewart et al., 2017). Weeds also bottles or 23-kg bags), which increases the United States and commonly grow in ditches, may be introduced with mowers and other cost considerably for homeowners managing sloughs, or in floating mats (Tobe et al., lawn equipment or wind. Once in the land- small areas. Glyphosate-resistant biotypes of 1998). Although lawns are not typical of a scape, weeds may persist through high re- weeds such as Conyza canadensis (L.) Conq. wetland habitat, excessive irrigation can in- productive rates or the ability to tolerate (horseweed) pose the same challenges. crease incidence and spread of some native landscape labeled herbicides and other treat- Vining weeds in landscapes commonly wetland species such as pennywort. In a study ment options. When desirable ornamentals or are reported as problematic because of the by Busey and Johnston (2006) H. umbellata turf is present, chemical control options are lack of selective herbicide options, and many L. (dollarweed) increased in cover and bio- more limited due to high potential for non- of these species grow very quickly among mass with increasing irrigation and fertiliza- target damage. If control options are lacking, desirable ornamental plants. Parthenocissus tion in a Stenotaphrum secundatum (Walt.) inputs intended for the landscape, such as quinquefolia (L.) Planch (virginia creeper) is Kuntze (st. augustine grass) lawn. In se- fertilizer, can cause these weeds to grow and a native vining plant that grows on ornamen- verely wilted lawns, St. Augustine showed spread further (Blackshaw et al., 2003). tal plants or fences in landscapes and consid- stress, and the cover of other weeds in- Problematic landscape weeds may not nec- ered a weed. Although not as competitive as creased, including native species surinam essarily outcompete ornamentals for re- some invasive vines, virginia creeper has sedge (Cyperus surinamensis Rottb.), thin sources but can create aesthetic issues at shown ability to reduce growth of native paspalum (Paspalum setaceum Michx.), even very low levels for some homeowners. trees, reducing height of Liquidambar syraci- and southern sida (Sida acuta Burm f.). A survey by Varlamoff et al., (2001) showed flua (sweetgum) by more than 30% in a 2- Invasive plants will presumably have 76% of Georgia residents rated a weed-free year field study (Dillenburg et al., 1993). a greater response to high nitrogen availabil- lawn as important, and previous research Several studies have examined response of ity compared with natives. Rickey and showed weed coverage thresholds were virginia creeper to herbicides (Richardson Anderson (2004) showed that the invasive 10% (Carpenter and Meyer, 1999). et al., 2009; Tworkoski et al., 1988; Tworkoski exotic grasses Phragmites australis Cav. Introduced invasive plants cost millions and Young, 1990). Most of the herbicides Trin. Ex Steud. (common reed) benefited of dollars each year to manage, threaten evaluated (2,4-D, triclopyr, hexazinone, glyph- from additional nitrogen to a much greater biodiversity, and reduce property values. In osate) on virginia creeper are not labeled for degree than the native Spartina pectinata contrast, native plants are promoted for the use in landscapes or would cause significant Bosc ex Link (prairie cordgrass) and, thus, many benefits they provide, including their nontarget damage. would be able to outcompete prairie cord- aesthetic value, providing food for wildlife, Other native vining weeds commonly grass in high nitrogen environments. How- attracting and supporting pollinators, and are found in landscapes include Campsis radi- ever, Lowe et al. (2002) reported no popular among homeowners (Helfand et al., cans L. Seem. Ex Bureau (trumpet creeper) difference in nitrogen response between two 2006). Native plants also very commonly and Toxicodendron radicans (L.) Kuntze native plant species, including blue grama promoted for their low-maintenance charac- (eastern poison ivy). Trumpet creeper is (Bouteloua gracilis H.B.K. Lag.) and western teristics. Native plants often are indeed low a troublesome weed in cotton (Gossypium wheatgrass [Pascopyrum smithii (Rybd.) A. maintenance in terms of water or pesticide spp.) fields and forestry (Webster, 2001) and Love], and four exotic species, including needs, as they are adapted to local environ- also can become a management issue in cheatgrass (Bromus tectorum L.), leafy mental conditions. However, as outlined landscapes because it often is planted for spurge (Euphorbia esula L.), canada thistle here, many native plants can become aggres- ornamental purposes and quickly grows to (Cirsium arvense L.), and russian knapweed sive in anthropogenic environments and trou- unmanageable levels. Trumpet creeper roots (Centaurea repens L.). In a meta-analysis, blesome as the result of our own expectations extensively when the vine has soil contact, Davidson et al. (2011) reported that invasive or preferences. Many of the species outlined making handweeding difficult, as stem frag- plants have greater phenotypic plasticity than in this manuscript would not be planted for ments left behind can form new shoots co-occurring noninvasive plants, but this aesthetic purposes, but it is important to (Edwards and Oliver, 2004). might not be related to performance or evaluate and document aggressive tendencies Poison ivy lacks vigorous growth charac- fitness. Daehler (2003) reviewed invasive of native plants under different environmen- teristic of trumpet creeper or virginia creeper and native plant comparison studies and tal conditions, rather than applying broad but is difficult to control selectively when found 79 studies showing there were no generalizations such as classifying all natives growing on trees and causes severe dermati- differences in growth rate, competitive abil- as ‘‘low maintenance.’’ This is especially tis, making manual removal a health hazard ity, or fecundity between the invasive and important when considering the confusion (Gladman, 2006). Poison ivy has been listed native plant pairs and that the performance of and many challenges that arise when basing as one of the most troublesome landscape the invaders depended on the growing con- native status on geopolitical boundaries. Fu- weeds (Van Wychen, 2016), although many ditions. In 55 comparisons that involved ture research should focus on identifying herbicides, including ready-to-use mixtures, more than one growing condition, the native the role that different environmental condi- available to homeowners, provide control plant performed as well or better than tions or various maintenance practices have (Wehtje and Gilliam, 2012). the invasive plant. Although landscapes are in the unwanted spread of native species.
HORTSCIENCE VOL. 53(9) SEPTEMBER 2018 1247 Additional information in this area could help depth affects weed germination. J. Environ. Kuester, A., J.K. Conner, T. Culley, and R.S. direct the selection of native plants for Hort. 27:85–90. Baucom. 2014. How weeds emerge: A taxo- ornamental purposes. If a native species had Colautti, R.I. and H.J. MacIsaac. 2004. A neutral nomic and trait-based examination using United a tendency to spread uncontrollably in a given terminology to define ‘invasive’ species. Di- States data. New Phytol. 202:1055–1068. situation, another native species or a nonin- vers. Distrib. 10:135–141. Lawton, J.H. 1988. Biological control of bracken in Cousens, R. 1985. A simple model relating yield loss Britain: Constraints and opportunities. Philos. vasive, non-native species could be chosen to weed density. Ann. Appl. Biol. 107:239–252. Trans. R. Soc. Lond. B Biol. Sci. 318:335–355. instead. Although many aggressive native Daehler, C.C. 2003. Performance comparisons of Li, W., J. Luo, X. Tian, W.S. Chow, Z. Sun, T. species have been identified in this manu- co-occurring native and alien invasive plants: Zhang, S. Peng, and C. Peng. 2015. A new script as being problematic in landscapes, Implications for conservation and restoration. strategy for controlling invasive weeds: Select- these species serve critical ecological func- Ann. Rev. Ecol. Evol. Syst. 34:183–211. ing valuable native plants to defeat them. Sci. tions in their natural habitat. An additional Davidson, A.M., M. Jennions, and A.B. Nicotra. Rep. 11004. area that deserves further investigation is 2011. Do invasive species show higher pheno- Lonsdale, W.M. 1999. Global patters of plant how to use the aggressive growth and re- typic plasticity than native species and, if so, invasions and the concept of invisibility. Ecol- productive abilities of these native plants for is it adaptive? A meta-analysis. Ecol. Lett. 14: ogy 80:1522–1536. environmental benefits. As detailed in Li 419–431. Lovell, S.J., S.F. Stone, and L. Fernandez. 2006. Davis, M. and K. Thompson. 2001. Invasion termi- The economic impacts of aquatic invasive et al. (2015), some of the more-aggressive nology: Should ecologists define their terms dif- species: A review of the literature. Agr. Resour. native species could be used as management ferently than others? No, not if we want to be of Econ. Rev. 35:195–208. tools to outcompete invasive non-native any help! Bull. Ecol. Soc. Amer. 82:206. Lowe, P.N., W.K. Lauenroth, and I.C. Burke. 2002. plants in different environments (Li et al., Dillenburg, L.R., D.F. Whigham, A.H. Teramura, Effects of nitrogen availability on the growth of 2015). A common mantra of landscape de- and I.N. Forseth. 1993. Effects of below- and native grasses and exotic weeds. J. Range Mgt. sign is to select the right plant for the right aboveground competition from the vines Loni- 55:94–98. place. When selecting plants for a landscape, cera japonica and Parthenocissus quinquefolia Mack, R.N. 1996. Predicting the identity and fate environmental benefits, aesthetic value, and on the growth of tree hos Liquidambar styraci- of plant invaders: Emergent and emerging long-term maintenance needs, including the flua. Oecogia 93:48–54. approaches. Biol. Conserv. 78:107–121. potential for unwanted spread, should be Dunn, P.H. 1979. The distribution of leafy spurge Marble, S.C., A.K. Koeser, G. Hasing, D. (Euphorbia esula) and other weedy Euphorbia McClean, and A. Chandler. 2017. Efficacy considered regardless of native status. spp. in the United States. Weed Sci. 27:509–516. and estimated annual cost of common weed Edwards, J.T. and L.R. Oliver. 2004. Emergence control methods in landscape planting beds. Literature Cited and growth of trumpetcreeper (Campus radi- HortTechnology 27:199–211. Altland, J.E., C.H. Gilliam, and J.W. 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1248 HORTSCIENCE VOL. 53(9) SEPTEMBER 2018 Implications for regulation of introductions. No. SS-AGR-357. 7 Mar. 2018.
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