Minnesota Invasive Terrestrial Plants & Pests Center New Species Evaluation

Cotoneaster lucidus Schltdl. (Hedge cotoneaster)

Evaluated: A.C. Morey; Reviewed: R.C. Venette (1/14/20)

OVERVIEW:

Common names: shiny cotoneaster, hedge cotoneaster, Peking cotoneaster (sometimes) Synonyms: Cotoneaster acutifolius var. lucidus, C. sinensis Hort., C. acutifolia Lindl., (not Turcz.)

Cotoneaster lucidus is a deciduous shrub native to central and eastern Asia, especially the Lake Baikal region and Altai Mountains, a mountain range where Russia, China, Mongolia, and Kazakhstan intersect. Some consider this species to now be a variety of C. acutifolius (also called the Peking cotoneaster), a native of northern China. The later species is dull green and hairy compared to C. lucidus. The difference in ecological and agronomic traits between the two is unclear. This likely also confounds current estimates of distribution. EDDMapS has separate entries for C. lucidus (map only) and C. acutifolius var. lucidus (with no data), and no entry for C. acutifolius. Conversely, the USDA-NRCS Plants Database has map entries for C. lucidus (with a different distribution than EDDMapS) and C. acutifolius, but not for C. acutifolius var. lucidus.

MAJOR KNOWLEDGE GAPS ASSOCIATED WITH ASSESSMENT:

 Current distribution (uncertainty with identification)  Effect on native communities  Effect on ecosystem services  Economic impact of control/regulation (e.g. industry value)  Dispersal capacity and vectors  Reproductive capacity

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ARRIVAL Proximity to Minnesota: VERY HIGH

RANKING Very High Pest is known to occur in Minnesota Pest occurs in Wisconsin, Iowa, South Dakota, North Dakota, Manitoba or High Ontario Medium Pest occurs in North America Low Pest is not known to occur in North America

The naturalized distribution of C. lucidus in North America seems uncertain (see taxonomic notes above).

One database shows occurrence in four Minnesota counties – Ramsey, St. Louis, Lake, and Cook Co. – and one northwestern county in Wisconsin (EDDMapS 2019). Herbarium records confirm the MN county records, dating from 2004 to present (UMN-Bell 2019). Another database shows state records for Wisconsin, Montana, and Colorado only (USDA-NRCS 2019).

It is noted that C. lucidus is considered a woody landscape species that is not known to naturalize in Iowa (Widrlechner et al. 2004). It is also a recommended landscape species in North Dakota (Herman and Chaput 2003). Its occurrence in Canada includes Quebec, Ontario, Manitoba, Saskatchewan, and Alberta (Canadensys 2019).

Existence of Pathways: HIGH

RANKING High Pathways for arrival of the pest in Minnesota are known to occur Pathways for the arrival of the pest in Minnesota are conceivable, but not Medium known to occur Low Pathways for arrival of the pest in Minnesota are difficult to conceive

There are currently no regulations for C. lucidus in Minnesota and there are records of it in the state since at least 2004 (UMN-Bell 2019).

The most likely pathway into Minnesota is intentional planting: C. lucidus is one of many Cotoneaster species grown in North America as popular ornamental plants (Slabaugh and Shaw 2008; CBG 2019). It is a species often used in conservation plantings (Slabaugh and Shaw 2008) and recommended for landscaping in Minnesota (Meyer, Brown, and Zins 2007). Seeds and plants are widely available for purchase online and are brought into the state for sale at multiple retails locations (see Spread: Existence of Pathways).

Additional entry into Minnesota via bird-dispersed seeds is also possible (see Innate Dispersal Capacity); the species is documented for all Canadian provinces

2 | C . l u c i d u s surrounding Minnesota (Canadensys 2019) and a Wisconsin county (Bayfield Co.) very near the shared border (EDDMapS 2019).

Innate Dispersal Capacity: MODERATELY LOW

RANKING Maximum recorded dispersal >500 km per year (or moves in low level Very High jets/ upper atmosphere) High Maximum recorded dispersal 500-250 km per year Moderate Maximum recorded dispersal 100-250 km per year Maximum recorded dispersal 1-100 km per year (wind dispersal; flowing Moderately Low water) Maximum recorded dispersal <1 km per year (movement through soil; Low splash dispersal)

Seeds of C. lucidus, like other Cotoneaster sp., are dispersed by birds such as blackbirds and other thrushes (Pliszko 2014; Boer 2014). Though no quantitative estimates of dispersal distance could be found for C. lucidus, some note that the bird dispersal distance for Cotoneaster sp. is “relatively low” or over “short distances linked to the roost locations of birds” (Boer 2014; Dickoré and Kasperek 2010). However, others consider bird-dispersal of Cotoneaster sp. “long-distance” and note other animals may also act as dispersers of viable seed (Wotton and McAlpine 2015; Piqueray, Mahy, and Vanderhoeven 2008; Starr, Starr, and Loope 2003; Konig 2018). Therefore, a rating of ‘moderately low’ was assigned here.

ESTABLISHMENT AND PERSISTENCE

Suitability of Minnesota Climate: HIGH

RANKING High >40% of Minnesota is predicted to be suitable Medium >20 to 40% of Minnesota is predicted to be suitable Low >0 to 20% of Minnesota is predicted to be suitable Negligible No part of Minnesota is suitable

The minimum USDA hardiness zones reported for C. lucidus vary somewhat, with some sources reporting up to Zone 4 (e.g., Univ. of Connecticut, Missouri Botanical Gardens) and others up to Zone 3 (e.g., Univ. of Illinois Extension, Oregon State University, Chicago Botanic Gardens). The Minnesota Department of Agriculture (MDA 2018) and Gertens (www.plants.gertens.com), a Minnesota-based nursery, purports it is hardy to Zone 2 and 2a, respectively. Survival to any of these zones would allow climatic suitability in >40% of the state.

Based on the current point records for Minnesota (EDDMapS 2019), most occurrences appear in Zones 4a or warmer/higher, but one (near Soudan, MN) is

3 | C . l u c i d u s noted in a Zone 3a/3b region. Therefore, this assessment will assume C. lucidus is hardy to Zone 3, which would include all of Minnesota.

Presence of Hosts: HIGH

RANKING High >10% of Minnesota with suitable hosts (or habitat for weeds) Medium >1 to 10% of Minnesota with suitable hosts (or habitat for weeds) Low >0 to 1% of Minnesota with suitable hosts (or habitat for weeds) Negligible 0% of Minnesota with suitable hosts (or habitat for weeds)

In its native range, C. lucidus occurs on rocky slopes, along rivers, and coniferous forests (Pliszko 2014).

In its invaded range, C. lucidus often escapes cultivation to spread to nearby forests, particularly conifer and oak (Pliszko 2014). Records in Minnesota indicate growth in forested understory (pine and spruce), along paths and roadsides within urban and semi-natural areas, and near waterfronts.

Considering only non-interstate roadways, there are ~123,394 miles in Minnesota (Williams 2005). Assuming ‘roadside’ habitat could occur within 100ft of the road edge on either side, that equates to 4,674 square miles, or ~5.7% of total state land. Of the estimated 7,719,200 acres of riparian land in Minnesota, 34.5% is forested (2,663,124 acres) (MN-DNR 2001). This accounts for about 5.2% of Minnesota’s terrestrial land. Pine and spruce forests in Minnesota cover approximately 5.6 million acres (Hillard 2018), or ~11% of state land.

Even if only half of these three habitat estimates were suitable, their combined area would still be >10% of Minnesota.

Hybridization/Host Shift: MEDIUM

RANKING High Species reported to hybridize or has undergone a documented host shift Medium Species in the same genus have been reported to hybridize/shift hosts Low Hybridization/Host shifts have not been reported for this genus or species

Intraspecific hybrids in Cotoneaster are putatively known (Dickoré and Kasperek 2010). No documentation of naturally-occurring C. lucidus hybrids are reported, though the taxonomic uncertainty within the genus (Dickoré and Kasperek 2010) and species (Pliszko 2014) is noted.

Cotoneaster sp. are apomictic (asexual reproduction through seed) and therefore many variants occur within each species. This variation has been used in commercial cultivar and hybrid development (Slabaugh and Shaw 2008).

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SPREAD

Existence of Pathways: HIGH

RANKING High Pathways for arrival of the pest in Minnesota are known to occur Pathways for the arrival of the pest in Minnesota are conceivable, but not Medium known to occur Low Pathways for arrival of the pest in Minnesota are difficult to conceive

Cotoneaster lucidus has been in Minnesota and spreading for more than 5 years and is known to be spread by humans.

Cotoneaster lucidus is one of many Cotoneaster species grown in North America as a popular ornamental plant (Slabaugh and Shaw 2008; CBG 2019). It is a species often used in conservation plantings (Slabaugh and Shaw 2008) and recommended as a good species to grow in “tough” garden sites in Minnesota (Meyer, Brown, and Zins 2007). Seeds and plants are widely available for purchase online (e.g., naturehills.com, amazon.com, hobbyseeds.com, mckaynursery.com) and are advertised as sold through many local retail outlets within the state (e.g., plants.gertens.com, pahls.com, plants.jimwhitingnursery.com, sunnyside- gardens.com, grussendorfnursery.com).

Additional movement of C. lucidus within Minnesota via bird-dispersed seeds and inadvertent movement of vegetative fragments is also possible (see Innate Dispersal Capacity).

Dispersal Capacity-Reproductive Potential: HIGH

RANKING High Annual reproductive potential (r) of pest is >500 descendants per year Medium Annual reproductive potential (r) of pest is 100 to 500 descendants per year Low Annual reproductive potential (r) of pest is <100 descendants per year

Each C. lucidus fruit has an average of 3 seeds (range 1-5) (Slabaugh and Shaw 2008). Estimates on the number of fruits produced by an individual C. lucidus could not be found. However, estimates for other Cotoneaster species are stated as “thousands” per individual (VRO 2019; CAL-IPC 2004).

A North Dakota nursery recorded an average seedling yield for C. lucidus of 30% (Slabaugh and Shaw 2008). Therefore, if 2,000 fruits were produced, 6,000 seeds could result. Assuming a 30% yield, 1,800 seedlings could result from one reproductive C. lucidus.

C. lucidus can also be propagated vegetatively through stem fragments (Slabaugh and Shaw 2008; Boer 2014); however, the effect of this on annual reproductive output is unknown.

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Extent of Invasion: MODERATE

RANKING Very High >60 countries likely to have established populations of the pest High 30-60 countries likely to have established populations of the pest Moderate 15-29 countries likely to have established populations of the pest Moderately Low 7-14 countries likely to have established populations of the pest Negligible 1-7 countries likely to have established populations of the pest

Cotoneaster lucidus is currently documented in four (4) Minnesota counties – Ramsey, St. Louis, Lake, and Cook Co. – with herbarium records dating from 2004 (EDDMapS 2019; UMN-Bell 2019).

Given the extent of climate and habitat suitability would unlikely limit further spread of C. lucidus in Minnesota (see Suitability of Minnesota Climate and Presence of Hosts), the potential invasion extent within the state in 10 years is estimated by its innate dispersal potential and its historical rate of spread:

Assuming a 50km/year spread via innate dispersal from the counties with current record of occurrence, a 500km radius would include all 87 counties within 10 years. Based on the historical county-level spread (4 counties in 15 years), about 2-3 counties would be further invaded within 10 years, for a total of 7 counties.

Considering both of these estimates and that the current state distribution is likely an underestimation, it is estimated here that at least a ‘moderate’ extent of invasion is reasonable.

Existence of Vectors: HIGH

RANKING High Vectored by birds or long distance insect migrants Medium Vectored by insects or bats Low Vectored by other mammals Negligible No evidence of any vectors

Seeds of C. lucidus, like other Cotoneaster sp., are dispersed by birds such as blackbirds and other thrushes (Pliszko 2014; Boer 2014). Other Cotoneaster sp. seeds are also dispersed by other animals (Wotton and McAlpine 2015; Piqueray, Mahy, and Vanderhoeven 2008; Starr, Starr, and Loope 2003; Konig 2018), but this has not been explicitly documented for C. lucidus.

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IMPACT

Problem Elsewhere: MEDIUM

RANKING High Noted as a problem within its native range and areas where it has invaded Medium Noted as a problem only in areas where it has invaded Low Not reported as a problem elsewhere

There is no documentation of C. lucidus being a problem in its native range of central and eastern Asia.

In its invaded range in Europe, C. lucidus is increasingly recognized as problematic, due to its ability to escape cultivation and outcompete native species and for its susceptibility/vectoring of fire blight (Kõiva 2003; Pliszko 2014). It has been reported as “a casual or established alien with invasive capacity” in central, eastern, and northern Europe (Pliszko 2014).

In its invaded range in North America, C. lucidus is currently viewed as a desirable ornamental hedge plant (e.g. (Meyer, Brown, and Zins 2007). Though it is recognized as a host of fire blight and other pests, these are viewed as pests to control in order to preserve C. lucidus, rather than a justification to consider C. lucidus problematic/invasive.

Impact to Yields and Marketability: MEDIUM

RANKING High >$5 million Medium $5 million to 0.5 million Low <$0.5 million

There are no documented, direct negative impacts to crop yields or marketability due to the presence of C. lucidus.

However, C. lucidus as a host of fire blight (Erwinia amylovora), so would indirectly threaten apple and pear crops and any related ornamental groups (e.g., Pyracantha, Sorbus, Crataegus) (Norelli, Jones, and Aldwinckle 2003; Slabaugh and Shaw 2008).

Nationwide, the commercial value of apple production was ~ $3.6 billion in 2017 (nass.usda.gov). Nationwide, fire blight costs U.S. apple growers ~$100 million annually (WSU 2018). Minnesota apple production was valued at $18.5 million in 2017 (Lofthus 2018). If the same loss of value was assumed for Minnesota as is nationwide (i.e., 2.8% of 2017 national value was lost to fire blight), then ~$514,000 would be lost in Minnesota apples alone due to sustained fire blight infection.

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Costs of Quarantine or Other Mitigation (annual): LOW

RANKING High >$5 million Medium $5 million to 0.5 million Low <$0.5 million

There is no information regarding the horticultural value of C. lucidus in the United States (or Minnesota), nor for that of ornamental Cotoneaster, broadly. Therefore, an estimate of its quarantine costs is unknown, though a species-specific quarantine would likely be difficult. The Netherlands and Belgium both determined that bans on sale of unwanted Cotoneaster sp. would be infeasible due to the widespread value of the genus as an ornamental (Boer 2014).

Cotoneaster seeds may remain viable for up to 5 years, so repeated control would be needed. However, it seems that a combination of cutting and application with glyphosate may provide effective control of Cotoneaster (if done repeatedly on any regrowth) (Boer 2014). Given the current limited distribution of plants in Minnesota (EDDMapS 2019) and lacking any other information, it is assumed here that overall mitigation costs would be low.

Impacts to Recreation or Real Estate (annual): NONE

RANKING High >$5 million Medium $5 million to 0.5 million Low <$0.5 million None $0

There are no documented negative impacts to recreation or real estate due to the presence of C. lucidus.

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Consequences to Native Species (Score): 3

References are only needed for the “worst case” situation.

RANKING Could reasonably be expected to affect federally listed Threatened and 5 Endangered Species Could directly, negatively impact pollinator 4 Causes local loss of native species 4 Lowers density of native species (empirical support) 3 Infection to native fauna or flora 2 Consumes native fauna or flora 2 Production of toxic substances including allelochemicals 2 Lowers density of native species (presumed due to dense thicket or vining) 2 Host for recognized pathogens/parasites of native species 1 None of the above apply 0

Documentation of the impact of C. lucidus on native communities is generally sparse. It can rapidly spread into a new area by root-suckering and form mono-dominant thickets (Pliszko 2014). In Europe, this intensive growth has been implicated in displacing native species, including those rare and endangered (Pliszko 2014; Straigyte and Benicsis 2011). Other species of Cotoneaster have been reported to act similarly and “shade out and smother” surrounding vegetation (Boer 2014; Konig 2018; Starr, Starr, and Loope 2003).

Cotoneaster is a susceptible host of fire blight, a disease caused by the bacteria Erwinia amylovora that also impacts apples, pears, and related species (Norelli, Jones, and Aldwinckle 2003; Slabaugh and Shaw 2008).

Consequences to Ecosystem Services (Score): 1

RANKING Modification of soil, sediments, nutrient cycling Alteration of genetic resources Alteration of biological control Changes in pollination services Alteration of erosion regimes Affects hydrology or water quality (includes effects of management) Creates a fire hazard Interferes with carbon sequestration

Documentation of the impact of C. lucidus on ecosystem services is lacking. Cotoneaster species invading coast dunes in the Netherlands were shown to permanently change the vegetation structure if not managed (Boer 2014). It is assumed that local displacement of native species by C. lucidus would alter local soil communities and cycling. Other effects are undocumented.

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Facilitate Other Invasions: HIGH

Invasion by the organism could lead to invasions of other species.

RANKING High The invasive species has facilitated invasions elsewhere The invasive species is a plant or animal that could reasonably be expected Medium to be a host or vector of another invasive species The species has not been reported to facilitate invasion elsewhere and is Low not likely to directly aid in the invasion of other species

Like other Cotoneaster, C. lucidus is a host to the bacterial pathogen, Erwinia amylovora, which causes the disease fire blight of plants in family Rosaceae (CABI 2019). However, E. amylovora is native to North America (Johnson 2000), and therefore not considered invasive for this assessment.

In Wisconsin, C. lucidus was considered an important reservoir for the invasive Eurasian sawfly, the pear slug (Caliroa cerasi), an economically-damaging pest of ornamental Prunus and Crataegus (Raffa and Lintereur 1988). Cotoneaster lucidus is also a host for oystershell scale (Herman and Chaput 2003) and the genus is a host of the invasive Light Brown Apple Moth (Epiphyas postvittana) (Brockerhoff et al. 2011).

REFERENCES

Boer, E. 2014. “Risk Assessment Cotoneaster.” Leiden, Netherlands: Naturalis Biodiversity Center. Brockerhoff, E.G., D.M. Suckling, C.E. Ecroyd, S.J. Wagstaff, M.C. Raabe, R.V. Dowell, and C.H. Wearing. 2011. “Worldwide Host Plants of the Highly Polyphagous, Invasive Epiphyas Postvittana (Lepidoptera: Tortricidae).” Journal of Economic Entomology 104 (5): 1514–24. https://doi.org/10.1603/EC11160. CABI, CAB International. 2019. “Datasheet: Erwinia Amylovora (Fireblight).” Invasive Species Compendium. Wallingford, UK: CAB International, Invasive Species Compendium. 2019. https://www.cabi.org/isc/datasheet/21908. CAL-IPC, California Invasive Plant Council. 2004. “Cotoneaster Lacteus.” Plant Assessment Form. 2004. https://www.cal-ipc.org/plants/profile/cotoneaster- lacteus-profile/. Canadensys. 2019. “Cotoneaster Lucidus Schlechtendal.” Database of Canadian Vascular Plants (VASCAN). 2019. http://data.canadensys.net/vascan/taxon/8644. CBG, Chicago Botanic Gardens. 2019. “Cotoneaster Lucidus.” Plant Finder. 2019. https://www.chicagobotanic.org/plantcollections/plantfinder/cotoneaster_luci dus--shining_cotoneaster. Dickoré, Wolf Bernhard, and Gerwin Kasperek. 2010. “Species of Cotoneaster (Rosaceae, Maloideae) Indigenous to, Naturalising or Commonly Cultivated in Central Europe.” Willdenowia 40 (1): 13–45. https://doi.org/10.3372/wi.40.40102. EDDMapS, Early Detection and Distribution Mapping System. 2019. “Hedge Cotoneaster, Cotoneaster Lucidus Schltdl.” Tifton, GA: The University of Georgia

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- Center for Invasive Species and Ecosystem Health. https://www.eddmaps.org/distribution/uscounty.cfm?sub=18190. Herman, Dale E., and Larry J. Chaput. 2003. “Trees and Shrubs of North Dakota.” EB- 38 (Revised). Fargo, ND: North Dakota State University Extension Service. http://mcscd.com/wp-content/uploads/2014/06/NDSU-Extn-Svc-Trees- Shrubs-guide.pdf. Hillard, Scott. 2018. “Forests of Minnesota, 2017.” Newtown Square, PA: USDA-Forest Service, Northern Research Station. https://www.fs.fed.us/nrs/pubs/ru/ru_fs154.pdf. Johnson, K.B. 2000. “Fire Blight of Apple and Pear.” The Plant Health Instructor. St. Paul, MN: The American Phytopathological Society. https://doi.org/10.1094/PHI-I-2000-0726-01. Kõiva, E. 2003. “Possibility of Appearance of Fire Blight Erwinia Amylovora in Estonia.” Agronomy Research 1 (2): 145–60. Konig, Natalie. 2018. “Simon’s Cotoneaster, Cotoneaster Simonsii Baker.” Anchorage, AL: Alaska Center for Conservation Science, University of Alaska Anchorage. Lofthus, Dan. 2018. “Minnesota Ag News – 2017 Apples.” Washington, DC. www.nass.usda.gov. MDA, Minnesota Department of Agriculture. 2018. “Cold Hardiness List.” 2018. https://www.mda.state.mn.us/plants-insects/cold-hardiness-list. Meyer, M., D. Brown, and M. Zins. 2007. “The Best Plants For 30 Tough Sites.” Master Gardener Bulletin. St. Paul, MN: University of Minnesota Extension Service, Master Gardner. https://conservancy.umn.edu/bitstream/handle/11299/51549/08464.pdf?seq uence=1&isAllowed=y. MN-DNR, Minnesota Department of Natural Resources. 2001. “Riparian Forests in Minnesota: A Report to the Legislature.” http://scholar.google.com/scholar?start=400&q=%22Gap+Analysis+Program%22 +++%22usgs%22&hl=en&as_sdt=0,6#7. Norelli, John L., Alan L. Jones, and Herb S. Aldwinckle. 2003. “Fire Blight Management in the Twenty-First Century: Using New Technologies That Enhance Host Resistance in Apple.” Plant Disease 87 (7): 756–65. https://doi.org/10.1094/PDIS.2003.87.7.756. Piqueray, Julien, Grégory Mahy, and Sonia Vanderhoeven. 2008. “Naturalization and Impact of a Horticultural Species, Cotoneaster Horizontalis (Rosaceae) in Biodiversity Hotspots in Belgium.” Belgian Journal of Botany 141 (2): 113–24. Pliszko, Artur. 2014. “Spontaneous Occurrence of Cotoneaster Lucidus Schltdl. in the Town of Augustów (NE Poland).” Steciana 18 (1): 33–36. https://doi.org/10.12657/steciana.018.005. Raffa, K.F., and G.L. Lintereur. 1988. “New Host Records and Developmental Notes on the Pear Slug Caliroa Cersasi (Hymenoptera: Tenthredinidae), Feeding on Cotoneaster and Chaenomeles Species.” The Great Lakes Entomologist 21 (2): 75–79. Slabaugh, Paul E., and Nancy L. Shaw. 2008. “Cotoneaster Medik.: Cotoneaster.” In Woody Plant Seed Manual Agriculture Handbook No. 727, edited by Franklin T. Bonner and Robert P. Karrfalt, 442–46. Washington, DC: U.S. Department of Agriculture, Forest Service. https://www.fs.usda.gov/treesearch/pubs/32639. Starr, F., K. Starr, and L. Loope. 2003. “Cotoneaster Pannosus.” Maui, Hawai’i: United States Geological Survey--Biological Resources Division Haleakala Field Station. http://www.starrenvironmental.com/publications/species_reports/pdf/cotone

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aster_pannosus.pdf. Straigyte, Lina, and Aurelijus Benicsis. 2011. “Impact of the Invasive Shrub on Spring Vetch (Vicia Lathyroides L.) in Palanga Park.” In Proceedings of the Biennial International Symposium, Forest and Sustainable Development, 295–300. Braşov, Romania. UMN-Bell, University of Minnesota Bell Museum. 2019. “Minnesota Biodiversity Atlas.” St. Paul, MN: University of Minnesota. https://bellatlas.umn.edu/. USDA-NRCS, United States Department of Agriculture Natural Resources Conservation Service. 2019. “Plant Profile: Cotoneaster Lucidus Schltdl.” Plants Database. 2019. https://plants.usda.gov/core/profile?symbol=COLU5. VRO, Victoria Resources Online. 2019. “Large Leaf Cotoneaster (Cotoneaster Glaucophyllus).” 2019. http://vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/weeds_large-leaf- cotoneaster. Widrlechner, Mark P., Janette R. Thompson, Jeffery K. Iles, and Philip M. Dixon. 2004. “Models for Predicting the Risk of Naturalization of Non- Native Woody Plants in Iowa 1.” Ecology 22 (March): 23–31. Williams, J. 2005. “Minnesota Highway Mileage.” St. Paul, MN: Research Department of the Minnesota House of Representatives. https://www.house.leg.state.mn.us/hrd/pubs/ss/ssmnhm.pdf. Wotton, Debra M., and Kate G. McAlpine. 2015. “Seed Dispersal of Fleshy-Fruited Environmental Weeds in New Zealand.” New Zealand Journal of Ecology 39 (2): 155–69. WSU, Washington State University. 2018. “Ph.D. Student Researcher Inoculates Trees in Race against Fire Blight.” WSU Insider, June 18, 2018. https://news.wsu.edu/2018/06/18/inoculating-for-fire-blight/.

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