Cuscuta japonica on Schinus molle. Photo credit Joanne Greer
Photo: Joanne Greer

Cuscuta japonica Risk Assessment

Synonyms: Cuscuta reflexa var. densiflora, Monogynella japonica

Common names: Japanese dodder

Cuscuta japonica -- California

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Created by: Scott Heacox
Created on: Sunday, Aug 6th, 2023
Evaluation Summary
Cuscuta japonica, or Japanese dodder, is an annual (occasionally perennializing in warm climates), holoparasitic (requires host plant to survive) vine native to a large portion of East Asia. Due to its parasitic nature, this plant has the ability to weaken or kill a wide range of host plant species through the leeching of nutrients, increasing host susceptibility to pathogens, and smothering under thick mats of the dodder's fast-growing, twining, spaghetti-like stems. Dodders, including Japanese dodder, are of economic concern due to their ability to affect the health and quality of the multitude of crop and ornamental plant species they infest. As such, all non-native Cuscuta species are listed as a federal noxious weeds in the United States. Japanese dodder has been introduced outside its native range into various parts of the US, including California, Texas, and South Carolina, although the population in South Carolina has been eradicated. It is also becoming a major pest of both agricultural and natural systems in Kenya. Japanese dodder normally produces abundant seeds which are typically spread by wind, water, or soil erosion. However, this plan can also readily propagate vegetatively from small pieces of stems, which is thought to be the primary mode of dispersal in California where this plant has not been observed to produce viable seeds. It is thought that this plant was introduced into California intentionally for its value as an herbal medicine in some cultures. Due to this plants ability to readily propagate from both seed and stem pieces, the potential for continued reintroduction for its medicinal uses, and its obvious negative associations with a variety of crop, ornamental, and native plant species, this evaluation finds Japanese dodder to have a "High Potential Risk" of invasiveness in California.
General Evaluation Information
Date of Evaluation: 
August 6, 2023
Evaluation Time (hrs): 
Not Recorded
Evaluation Status: 
Completed
Plant Information
Plant: 
Cuscuta japonica
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
Regional Information
Region Name: 
California
Climate Matching Map
These maps were built using a toolkit created in collaboration between GreenInfo Network, PlantRight, Cal-IPC, and Agricultural Sustainability Institute at UC Davis.
PRE Climate Map (external link)
Climate Matching Maps PDF: 
AttachmentSize
PDF icon ClimateMatch_California_Cuscuta_japonica.pdf1.12 MB
Invasive History and Climate Matching
1. Has the species (or cultivar or variety, if applicable; applies to subsequent "species" questions) become naturalized where it is not native?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Japanese dodder (Cuscuta japonica) is native to Eastern Asia, including China, Mongolia, Japan, Korea, Taiwan, and parts of Vietnam (Texas Invasive Species Institute 2014, Woodward and Quinn 2011, Lanini et al. 2010). This plant can now be found outside of its native range in Kenya (Rotich et al. 2021) and the US states of Texas, Florida, South Carolina, and California (Texas Invasive Species Institute 2014, Lanini et al. 2010, Invasive Plant Atlas 2018, Cal-IPC News 2006, Westbrooks and Eplee 1996, Tidwell 2008). Literature seems to indicate that most infestations in the US are centered around urban areas, where the dodder affects ornamental and agricultural woody trees and shrubs, however the dodder is also able to utilize some native species as hosts (Lanini et al. 2010, Tidwell 2008). Rotich and others (2021) state that Japanese dodder now ranges widely across Kenya, including some natural forests. Therefore, it appears that this species has some ability to naturalize in native ecosystems.
Reference(s): 
Invasive Plant Atlas of the United States (2018).  Japanese dodder. 2023,
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
2. Is the species (or cultivar or variety) noted as being naturalized in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
Cuscuta japonica is currently naturalized in multiple locations of California (Texas Invasive Species Institute 2014, Lanini et al. 2010, Invasive Plant Atlas 2018, Cal-IPC News 2006, Westbrooks and Eplee 1996, Tidwell 2008). Cuscuta japonica is also noted as naturalized in South Carolina (Westbrooks and Eplee 1996, Texas Invasive Species Institute 2014, Invasive Plant Atlas 2018, ODA 2015). According to the PRE Climate Match results, this portion South Carolina shares a climate match with California, although this species appears to have been eradicated from this area (Tidwell 2008).
Reference(s): 
3. Is the species (or cultivar or variety) noted as being invasive in the U.S. or world?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
Very High
Answer / Justification: 
Japanese dodder is federally listed in the United States as a noxious weed, and it is included in state invasive lists and laws in Oregon, Texas, South Carolina, and New Jersey (Invasive Species Atlas 2018), and it is considered a major invasive threat across multiple parts of Kenya, although there is some disagreement on the taxonomy of the exact species present here (Rotich et al. 2021, Mutitu 2020). Multiple sources note the potential for this plant to cause serious economic and environmental harm due to its ability to spread easily and weaken or kill ornamental, agricultural, and native plant species (Texas Invasive Species Institute 2014, ODA 2015, Cal-IPC 2006, Lanini et al. 2010, Rotich et al. 2021, Mutitu et al. 2020).
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
Invasive Plant Atlas of the United States (2018).  Japanese dodder. 2023,
4. Is the species (or cultivar or variety) noted as being invasive in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
3
Confidence Level: 
High
Answer / Justification: 
According to the Climate Match map, the only region that climatically matches California (besides California) where Japanese dodder occurs outside its native range is a small portion of South Carolina. The South Carolina Exotic Plant Pest Council (2014) lists this species at an "alert" status and has indicated that it has been eradicated from the state, however. Within California, this species is invasive in a variety of counties, including Redding, Yuba, Alameda, Contra Costa, Fresno, Los Angeles, and Sacramento (Cal-IPC 2006). All non-native Cuscuta species (including C. japonica) are included in the 2021 CDFA CCR 4500 Noxious Weeds list.
Reference(s): 
5. Are other species of the same genus (or closely related genera) invasive in a similar climate?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Many species of Cuscuta are listed on the Global Compendium of Weeds, some of which, such as Cuscuta reflexa, are listed as invasives in parts of India, Pakistan, and Nepal that share a similar climate to California (Randall 2017).
Reference(s): 
6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
This species is widespread across Asia. Although a large portion of its range in China matches California climate, the majority of Japanese dodder occurrence, mostly through other parts of China, Taiwan, Japan, and the Korean peninsula, do not match California climate (see Climate Match map).
Reference(s): 
Impact on Native Plants and Animals
7. Does this plant displace native plants and dominate (overtop or smother) the plant community in areas where it has established?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Aggressive dodder infestations can produce a thick mat of tangled stems that no doubt "smother" plants (Tidwell 2008), however discussion of this in literature appears to be very rare. Rather, most research centers on their propensity to smother plants via parasitism -- extracting water and nutrients to the point of weakening or killing its host plant (Sarić-Krsmanović and Vrbničanin 2017, Cal-IPC 2006, Lanini et al. 2010, Tidwell 2008).
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
I found no evidence that Japanese dodder, or other species of dodder, have been linked to a change in fire regime. The bulk of the vegetative matter of Japanese dodder consists of thin stem strands which would not serve as a significant fuel source, however dried mats of stems may encourage ignition. The plant is unlikely to alter fire regimes unless at extremely high density. Most infestations occur in urban or agricultural settings, so it is difficult to measure effects on natural fire regimes.
Reference(s): 
9. Is the plant a health risk to humans or animals/fish? Has the species been noted as impacting grazing systems?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
I found no evidence that Japanese dodder poses a significant toxic risk or has the ability to cause noteworthy mechanical injury to humans or other animals. Rather, Nice and others (2006) state that dodder species are nontoxic and palatable to some livestock. It is also valued for its wide range of potential medical uses (Noureen et al. 2019). However, it should be noted that there is other evidence that related species produce for some toxicity in livestock (Abutarbush 2013).
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
I found no discussion of Cuscuta japonica or other Cuscuta species causing impenetrable thickets or otherwise impacting wildlife movement. It's possible to infer that heavy infestations could affect wildlife by altering availability of bird nesting sites, however evidence is lacking. Heavy infestations may be more likely to occur in parts of California that do not experience frost (and hence have a longer or indefinite growing season), however more information is needed to determine the likelihood of this scenario.
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Vegetative reproduction is noted as the main mode of spread in California, where this species apparently does not produce viable seeds (Lanini et al. 2010, Nevada Department of Agriculture 2023, Tidwell 2008). Small pieces of plant stems, which can regrow into new plants, can be easily spread via uncleaned tools, movement of infected plants or plant pieces, and improper composting, as well as by animals that have come into contact with the plant (Lanini et al. 2010, Nevada Department of Agriculture 2023, Tidwell 2008). This plant has also be noted as perennializing in California (Tidwell 2008), which likely aids in sustaining infestations where viable seeds would otherwise be required for multi-year survival.
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
12. If naturally detached fragments from this plant are capable of producing new plants, is this a common method of reproduction for the plant?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Spread via transport of stem pieces is the primary, and potentially only, mode of reproduction in California where C. japonica seeds appear to be nonviable (Lanini et al. 2010, Nevada Department of Agriculture 2023, Tidwell 2008). Elsewhere, this plant appears to be able to reproduce both vegetatively and by seed.
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Japanese dodder is a prolific seeder across most of its range (Parker 2009, Tidwell 2008, Texas Invasive Species Institute 2014). However, this species apparently does not produce viable seed in California (Lanini et al. 2010, Tidwell 2008, Parker 2009). The reason behind this lack of viable seeds in California is unknown, but two hypotheses exist. First, this species is apparently self-sterile, and if populations are primarily clonal (descended from a single plant cutting), they would not be able to cross-pollinate; and second, Japanese dodder flowers unusually late in California, which may not provide enough time for seeds to fully develop before winter (Tidwell 2008, Parker 2009). Cuscuta japonica usually behaves as an annual, but the fact that C. japonica has been noted as perennializing in California is likely critical to its ability to persist for multiple years in spite of producing nonviable seeds (Tidwell 2008). The lower confidence level of this answer is to reflect this geographic variation in seed viability.
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Japanese dodder, as well as other dodder species, has the ability to produce more than 2000 seeds per plant per year (Texas Invasive Species Institute 2014, Mutitu et al. 2020, Saeed and Zaroug 1989). However, as discussed previously, this species has not been observed to produce viable seeds in California and may only persist here due to its ability to perennialize in some warmer climates (Lanini et al. 2010, Parker 2009, Tidwell 2008). The lower confidence level of this answer is to reflect this geographic variation in seed viability.
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
15. Is there significant germination (>25%) of seeds the next growing season, with no requirement of an infrequent environmental condition for seeds to germinate (i.e. fire) or long dormancy period?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Seeds of dodder species, including Japanese dodder, can exhibit a low rate of germination in the following growing season after seed set. Lanini and others (2010) state that around 5% of dodder seeds will germinate in the next year after production, and Parker (2009) states that germination occurs over a long period of time to avoid a scenario where all seeds germinate without a host present. However, the Texas Invasive Species Institute (2014) states that most seeds will germinate within one year after production. Also, as discussed in previous questions, this plant apparently does not produce viable seed in California and multi-year survival is likely aided by this plant's ability to perennialize in warmer climates (Lanini et al. 2010, Parker 2009, Tidwell 2008). The lower confidence level of this answer is due to this discrepancy of reported germination rates.
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
16. Does this plant produce viable seed within the first three years (for an herbaceous species) to five years (for a woody species) after germination?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
This plant is known to be a prolific seeder at most locations across the world (Texas Invasive Species Institute 2014, Mutitu et al. 2020, Saeed and Zaroug 1989). This plant is usually an annual, which means seed production must occur within one year (Parker 2009, Tidwell 2008, Texas Invasive Species Institute 2014). However, this plant has not been observed to produce viable seeds in California and multi-year survival is likely aided by this plant's ability to perennialize in warmer climates (Lanini et al. 2010, Parker 2009, Tidwell 2008).
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
17. Does this plant continuously produce seed for >3 months each year or does seed production occur more than once a year?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
I was unable to find specific seed production information for Cuscuta japonica. However, the Jepson eFlora (Costea and Stefanović 2012) list the time of flowering as September through November, so it is unlikely that this plant will produce seed for more than three months per year. However, it is worth noting that Jepson eFlora also shows 17 of 22 Cuscuta species in California flower for 4 or more months per year.
Reference(s): 
Dispersal
18. Are the plant’s propagules frequently dispersed long distance (>100 m) by mammals or birds or via domestic animals?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
The seed of Cuscuta japonica does not possess any special adaptations to aid in dispersal by animals (Parker 2009). However, some sources indicate that stem pieces can be transported by birds for use as nesting material (Parker 2009, Lanini et al. 2010), and this may play a role in outbreaks in California where C. japonica seeds are apparently nonviable. However, I could not find any compelling evidence to indicate that animal-borne dispersal is a frequent occurrence in California or elsewhere, and infestations in California are more likely influenced by human activity. Also, sources generally indicate that C. japonica seeds are usually spread by wind, water, or erosion, and that this is the primary means of reproduction across most of its range (Parker 2009, Lanini et al. 2010, Texas Invasive Species Institute 2014).
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Most sources indicate that wind- and water-borne seed dispersal is most common for this species (Parker 2009, Lanini et al. 2010, Texas Invasive Species Institute 2014). However, stem pieces seem to be primarily transported by a wide range of anthropogenic mechanisms including contaminated garden waste, improper composting, and transport of infected plants (Lanini et al. 2010, Nevada Department of Agriculture 2023, Tidwell 2008).
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
20. Are the plant’s propagules frequently dispersed via contaminated seed (agriculture or wildflower packets), equipment, vehicles, boats or clothing/shoes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
The seeds of Cuscuta japonica do not possess any morphological adaptations to aid in dispersal via attachment to animals/humans or vehicles, and is therefore not thought to be dispersed as such (Parker 2009). Spread via transport of stem pieces is the primary, and potentially only, mode of reproduction in California (Lanini et al. 2010, Nevada Department of Agriculture 2023, Tidwell 2008) and is most likely primarily due to human activity. However, it should be noted that state noxious weed laws prohibit movement of seeds or sale of crop seed from agricultural fields infected with dodder species which should help decrease instances of dispersal via agricultural products.
Reference(s): 
Lanini, W.T., Cudney D.W., Miyao G., & Hembree K.J. (2010).  Dodder. Pest Notes. 2023,
Evaluation Notes

One of the main issues I had evaluating this species regards how to treat the questions discussing seed viability and germination. Multiple sources discuss that this species has not produced viable seeds in California, although it is a prolific seeder elsewhere in the world. I answered these questions with the assumption that this plant may possess the ability to produce viable seed in California given proper conditions (presence of non-clonal populations, establishment in different climates, etc).

 

Question 17 -- for some reason I could not add the reference for Costea and Stefanović 2012.

Total PRE Score

  • < 13 : Low Potential Risk
  • 13 - 15 : Moderate Potential Risk
  • > 15 : High Potential Risk

PRE Score: 
17
Number of questions answered: 
20
Screener Confidence (%): 
76.0
PRE Content Access and Privacy
Organization: 
2023-2024 Western IPM Project
California Invasive Plant Council (Cal-IPC)
Evaluation visibility: 
Public - accessible to all site users

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