Ludwigia decurrens (winged water-primrose)

California Pest Rating
Ludwigia decurrens (winged water-primrose)
Myrtales; Onagraceae
Former Pest Rating:  Q
CURRENT Pest Rating:  A  |  Seed Rating:  P
Initiating Event:

This plant was been detected in California in 2011.

History & Status:

Winged water-primrose is an invasive weed that was identified in Butte County rice fields in 2011. Most infestations are along borders of fields and canals; however, this weed can thrive in the flooded environment within rice fields. Winged water-primrose can disperse through seeds and plant fragments floating in the irrigation water and tillage and harvest equipment.

Official Control: Butte County has been carrying out control in partnership with rice growers.

California Distribution:  Winged water-primrose occurs in several rice fields in Butte County, California. It has persisted in low number despite several years of attempted eradication.

California InterceptionsWinged water-primrose was found in a rice field inspection.

Other range: It is native to the southeastern U.S. and has been introduced into Japan where it is an invasive weed of rice.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score: 2

Low (1) Not likely to establish in California; or likely to establish in very limited areas.
Medium (2) may be able to establish in a larger but limited part of California.
High (3) likely to establish a widespread distribution in California.

Risk is Medium (2), as the plant could occur in wetlands such as the Delta as well as in rice fields.

2) Known Pest Host Range: Evaluate the host range of the pest. Score: 3

Low (1) has a very limited host range.
Medium (2) has a moderate host range.
High (3) has a wide host range.

Risk is High (3) as weeds do not require any one host, but grow wherever ecological conditions are favorable.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score: 3

Low (1) does not have high reproductive or dispersal potential.
Medium (2) has either high reproductive or dispersal potential.
High (3) has both high reproduction and dispersal potential.

Risk is High (3). The plant produces via numerous seeds and can spread rapidly in water, in poorly-cleaned seed, and on farming equipment. It is likely to have been introduced into California from a seed lot.

4) Economic Impact: Evaluate the likely economic impacts of the pest to California using the criteria below. Score: 3

A.  The pest could lower crop yield.

B.  The pest could lower crop value (includes increasing crop production costs).

C.  The pest could trigger the loss of markets (includes quarantines).

D.  The pest could negatively change normal cultural practices.

E.  The pest can vector, or is vectored, by another pestiferous organism.

F.  The organism is injurious or poisonous to agriculturally important animals.

G.  The organism can interfere with the delivery or supply of water for agricultural uses.

Low (1) causes 0 or 1 of these impacts.
Medium (2) causes 2 of these impacts.
High (3) causes 3 or more of these impacts.

Risk is High (3) as the plant can lower crop yields, trigger quarantines, and force changes in cultural practices.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A.  The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B.  The pest could directly affect threatened or endangered species.

C.  The pest could impact threatened or endangered species by disrupting critical habitats.

D.  The pest could trigger additional official or private treatment programs.

E.  The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score: 3

Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
High (3) causes two or more of the above to occur.

Risk is High (3) as the plant could invade the water systems of California, disrupt natural wetland communities and potentially lower biodiversity by invading wetlands.

Consequences of Introduction to California for Winged water-primrose:

Add up the total score and include it here. (14)

Low = 5-8 points
Medium = 9-12 points
High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. Score: Low (-1)

Not established (0) Pest never detected in California, or known only from incursions.
Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (13)

Uncertainty:

It is a weed of rice in other localities and seems similar in biology to its relatives that are also weeds of rice in California. So, the uncertainty is low.

Conclusion and Rating Justification:

A potentially significant weed in CA of both natural wetlands and rice fields. Deserves an A rating as it’s so invasive in Japan and other rice growing regions.

References:

Flora of North America Editorial Committee, eds.  1993+.  Flora of North America North of Mexico.  16+ vols.  New York and Oxford.

Chandrasena, J. P. N. R. 1988. Ludwigia decurrens Walt. – A new rice field weed in Sri Lanka. Journal of National Scientific Council, Sri Lanka 16: 97-103.

UC Rice Blog: Behavior of Winged Primrose Willow and Herbicide Options for Control. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7778


Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0312; plant.health[@]cdfa.ca.gov.


Comment Period:  CLOSED

The 45-day comment period opened on Monday, December 21, 2015 and closed on February 4, 2016.


Pest Rating:  A  |  Proposed Seed Rating:  P

11 thoughts on “Ludwigia decurrens (winged water-primrose)”

  1. Dear Dr. Kelch,

    The California Crop Improvement Association (CCIA) is the designated seed certifying agency in California. The CCIA inspects 20,000 to 25,000 acres of rice seed production annually, and certifies 150 to 180 seed lots annually. Approximately 90% of the rice seed planted in California is certified seed. The CCIA general standards state in Section 13.1.c “Presence of prohibited noxious weeds shall cause rejection of the field unless areas containing such weeds are clearly separated from the remainder of the field.” As viable seeds of Ludwigia decurrens would be present by the time of rice harvest, reclassification of this weed to an ‘A’ rated pest with a ‘P’ seed rating would formalize a zero tolerance policy for this weed in all fields producing certified seed. The current population range of Ludwigia decurrens is in close proximity to a number of fields producing classes of certified seed. A ‘P’ seed rating would be cause for rejection of certified rice seed production fields if the seed-bearing plant is in the field at the time of harvest.

    The current proposal states, “The plant produces via numerous seeds and can spread rapidly in water, in commercial seed, and on farming equipment. It is likely to have been introduced into California from a seed lot.” The seed size of Ludwigia decurrens is approximately ½ mm in length and ¼ mm in width. The seed capsules are approximately 2-3 cm long and ¾ cm wide. Seeds of this size are highly unlikely to pass through the conditioning process that planting seed undergoes in California, thus making dispersal through seed lots highly unlikely. Additionally, seed capsules of this size are too large to pass through the conditioning process.

    Fields producing certified seed often contain weeds with viable seeds at the time of harvest, especially late watergrass, early watergrass, barnyardgrass, redstem, sprangletop, smallflower umbrella sedge, and ricefield bulrush. Of these commonly observed weeds, only smallflower umbrella sedge (Cyperus difformis) and redstem/redberry (Ammannia spp.) have seed sizes as small as Ludwigia decurrens. It should also be noted that while redstem seeds are small, the seeds can pass through the conditioning process in the round seed pods (“berries”) which are of similar size to rice seed. In reviewing the 853 seed laboratory Reports of Analysis of all certified rice lots between 2010 and 2014 (2015 harvested seed is still being conditioned), a total of five (5) Reports of Analysis reported the presence of weed seed in the seed samples. Of these five (5) samples, three (3) contained Echinochloa spp., one (1) contained bulrush, and one (1) contained Ammannia spp.

    Taking into account that it is highly unlikely that the large seed capsule or the extremely small seed would pass through the rice conditioning process, while also considering the economic impact of rejection of certified seed fields containing noxious weeds with a ‘P’ (Prohibited) seed rating, we propose that the seed rating be removed or changed to an ‘R’ (Restricted) rating. An ‘R’ rating would allow for the presence of the weed in the field and have zero tolerance for the weed seed in certified lots.

    Sincerely,
    Timothy Blank
    California Crop Improvement Association
    Certified Rice Program Manager

    1. Certification of seed is not required. Certified seed is held to a high standard for a reason; to provide value added seeds to California and our trading partners. In addition, it is important to protect California agriculture from new pests that increase production costs and cause damage to the environment. Winged water-primrose is found as a rice weed in the southeastern U.S., Japan, SE Asia, and South America. It would be a good thing to eradicate it from California. Additionally, it would be best to exclude it from further introduction into California in commercial seed, regardless of how well that seed lot has been cleaned. Those growers who wish to produce the highest quality seed should exclude or eradicate weeds such as winged water-primrose from their fields.

  2. February 3, 2016

    Mr. Dean G. Kelch, Primary Botanist
    California Department of Food and Agriculture
    1220 N Street
    Sacramento, CA 95814

    RE: Comments on the proposal to change the current pest rating to A and the seed rating to P for the Ludwigia Decurrens (Winged Water-Primrose)

    Dear Mr. Kelch:

    The California Rice Commission (CRC) is a statutory organization representing the state’s rice industry encompassing 2,500 rice growers, 40 millers, and approximately 500,000 acres of farmland. On behalf of the California rice industry, we offer several solutions to the current proposal to change the pest rating of the Winged Water-Primrose.

    Our primary request is an extension of the comment period and deferral to reevaluate the proposal of changing the current rating to A, and the seed rating to P. The CRC suggests a change in the scoring if the current regulatory process does not allow for reevaluation of the weed pest.

    We ask that the California Department of Food and Agriculture extend the comment period another 45-days, and postpone the decision for a minimum of one year to reevaluate the criteria for the proposal. As a proactive industry, we have the tools to identify and control the pest if it remains under jurisdiction of the Butte County Agricultural Commissioner’s office. The weed issue was not strongly addressed under the previous regime at the county level. Recent changes in personnel have created the structure for collaboration in identification, control and management of the weed pest.

    It is our understanding that funding does not exist at the state level for weed control programs. The notice for the proposal to change the current rating provides linkage to rice industry-funded research that assists in identification and offers effective herbicides for control. The listed herbicides are registered in California for use on rice, right of ways and irrigation canals, and readily available to the growers and irrigation districts in Butte County.

    Outreach to local county entities has taken place with extensive collaboration on identification, education and control. The letter written by Dr. McKenzie, Director of the Rice Experiment Station, outlines the concept draft proposal for responsibilities of the local agencies, organizations and supporters.

    Our second suggestion is to adjust the scoring, if the current regulatory process does not allow for an extension of the comment period and postponement of the decision to change the ranking. We suggest a reconsideration of the proposal for changing the ranking to A and suggest the Winged Water-Primrose become a B-rated pest. The CRC recommends the following scoring:
    1) Climate/Host Interaction: Score 1
    Low (1) not likely to establish in California or likely to establish in very limited areas. The weed pest has remained at the location first discovered in Butte County.
    2) Known Pest Host Range: Score 3
    High (3) agree a weed does not require a host even though it appears rice is identified as the crop.
    3) Pest Dispersal Potential: Score 3
    High (3) has both high reproduction and dispersal potential even though the seeds are small and would filter out of any harvesting or milling equipment.
    4) Economic Impact: Score 1
    Low (1) from communication with other rice states, the weed pest does not lower crop yield, lower crop value or increase production costs, change normal cultural practices, injurious or poisonous to agriculturally important animals or interfere with water delivery or the supply of water for agricultural uses. It is not certain the weed pest can vector or is vectored by another pestiferous organism. The impact on trade or quarantine would be evident with the A ranking.
    5) Environmental Impact: No scoring
    The CRC provided no scoring, since we have not found data and information specific to California rice growing conditions.
    6) Post Entry Distribution and Survey Information: Score 1
    Low (1) pest has a localized distribution in California or is established in one suitable climate/host area (region).
    7) Final Score: 9-11
    Medium = 9-12 points. The CRC provided a range due to the uncertainty of item number 5, the Environmental Impact for California rice growing conditions.

    For the reasons provided in this comment letter, the CRC requests either an extension of the comment period and reevaluation to defer the decision or provide B ranking to maintain control by the Butte County Agricultural Commissioner. Please contact our office if you have questions or need additional information. Phone: 916-387-2264.

    Sincerely,

    Roberta L. Firoved
    Industry Affairs Manager

    1. I was discussing the primrose with Dr. Kassim Al-Khatib, Rice Weed Scientist at UCD, and he expressed concern that some pest ratings can prohibit field research being done to understand the biology and develop effective control protocols. Would this be the case with an A classification?
      Kent S. McKenzie

      1. Moving A rated pest propagules requires a state permit, but this is usually not a major inconvenience. It involves sanitation and security conditions that most researchers can meet with a little care.

  3. Butte County Rice Growers Association
    P.O. Box 128 Richvale, CA 95974 (530) 882-4261

    Dean G. Kelch, Primary Botanist
    California Department of Food and Agriculture 1220 N. Street
    Sacramento, CA 95814

    February 2, 2016

    Subject:
    CDFA’s Division of Plant Health’s Pest Ratings and Proposals Ludwigia de currens (winged water-primrose)

    Dear Mr. Kelch,
    I am writing to comment on the proposed reclassification of the winged water-primrose from a current pest rating of “Q” to a proposed pest rating of “A”.
    This reclassification raises two main concerns:
    1. The first concern is that it may impact our current seed production which currently takes place at the Rice Research Station in addition to seed growers within the localized area
    of the known pest.
    2. The second concern involves the potential for economic impact to the rice industry due to possibly phytosanitary restrictions that may be imposed due to this reclassification. This could impact local rice drying and storage facilities, grower production from fields and marketing organizations that export rice from the area.
    These two concerns are of such significance that a stakeholder group of interested parties are currently meeting to create an aggressive program to identify and control the winged water -primrose in 2016. We ask that CDFA delay the proposed reclassification of this weed pest to allow the control program to be implemented over the next growing season. There is significant concern about the A rating being exploited as a trade restriction to exporting California rice at a time when the industry is struggling with drought, competition, and access to foreign markets.
    As to reviewing the report, there are a few specific comments that I would like to raise in regards to the following sections:

    Official Control: Butte County Ag Commissioner (BCAC) has been monitoring the situation but lacks staffing time. There has been staff turnover and recently a new Ag Commissioner was named. Because of a lack of state funding for weed control, the county has had limited resources to address this issue.
    California Interception: It is our review that this weed does not survive in fields that are farmed conventionally. Registered Rice Herbicides such as grandstand control the weed effectively. The only known field where the plant survived was an organically grown field that did not treat the weed.
    Pest Dispersal Potential: This currently has a score of 3 (High). In this determination, seed is commercial seed is mentioned as a cause for spreading the pest. All commercial seed is grown and cleaned by approved state seed conditioners, and all seed sold has been approved by CCIA (California Crop Improvement Association). All seed has lab results by lot identifying germination and purity. Since the pest weed seeds are extremely small, they would clean out in the seed conditioning process and this is borne out by the small area location of the infestation. If the pest was being spread via seed, it would have shown up in random fields around the area, not concentrated in one geographic area. I believe that this score should be reduced.
    Economic Impact: This currently has a score of 3 (High).
    Item A. It is noted that the pest could lower crop yields. This has not been the case.
    Butte County Rice Growers Association just had its two highest yields per acre in its 101 year history during 2014 and 2015.
    Item C. This states that the pest could trigger the loss of markets, however this pest is in the Southern Rice area, and it has not contributed to a loss of markets.
    Item E. The pest can vector. We are not aware of this happening. Is there any evidence of this that can be documented?
    Item F. The organism is injurious or poisonous to agriculturally important animals.
    Again, we are not aware of this occurring. Is there any evidence of this that can be documented?
    Item G. The organism can interfere with the delivery of water. Per discussions with the Richvale Irrigation management, there is no evidence that this is causing delivery problems.
    Based upon all of the above facts, we believe this score should be reduced.
    In conclusion, we ask that CDF A hold back from making this reclassification and allow for the coalition of parties that is being formed to aggressively pursue a program to control this weed in the 2016. This coalition represents the Butte County Ag Commissioner, the Rice Research Station, Ag Drying and Storage Cooperatives, PCA’s/CCA’s, Irrigation Districts, land owners

    and the University of California. Together, we believe that we can make a difference in controlling the spread of this pest.
    Sincerely

    Carl D. Hoff President and CEO

    1. As required by Title 3, California Code of Regulations, section 3162 pest risk assessments follow a format with certain criteria; seed production is not among them. If the weed in question spreads further, it may impact seed production. Assigning a A rating to a Q rated plant should not affect seed production.

      Q rated pests are treated as if they are A rated in regulation. The proposed permanent rating of A should not affect regulation in this regard. As the seeds of winged water-primrose are much smaller than rice grains, there should be no problem in producing clean rice seed from lightly infested rice fields such as currently exist.

      The seed of this pest can be removed by cleaning seed. However, winged water-primrose may be spread by uncleaned seed. Even if this pathway were rated low risk as almost all seed is cleaned, this pest still has the ability to spread quickly via water, equipment, and even animals.

      The lettered list in the Proposed Pest Rating is a list of potential economic impacts. The PPR states that “Risk is High (3) as the plant can lower crop yields, trigger quarantines, and force changes in cultural practices.”
      .Risk analysis addresses potential as well as demonstrated risk. You state above that in fact this plant does potentially threaten markets. It has already changed cultural practices in infested areas. That it has not yet lowered crop yields is excellent news, but its known allelopathy and its behavior in other countries demonstrates a significant risk that it could do so if not controlled.

  4. TO: Dean G. Kelch, Primary Botanist
    California Department of Food and Agriculture (CDFA)

    FROM: Kent S. McKenzie, Director and Plant Breeder
    Rice Experiment Station (RES)

    RE: Division of Plant Health’s Pest Rating and Proposal
    Ludwigia decurres Winged Water-Primrose (WWP)

    The classification of the WWP as a category A pest by CDFA is of serious concern to this organization and the California Rice Industry because of:
    1. The production of certified classes of rice seed by the Rice Experiment Station and seed growers in the area. The Rice Experiment Station produces the foundation seed for more than 90% of California’s rice production. The presence of an A weed pest would disqualify a seed field.
    2. Possible phytosanitary issues with commercial rice production, storage, and its marketing worldwide. There is great concern about the A rating being exploited as a trade restriction/barrier for exporting California rice at a time when the California Rice Industry is struggling with drought, price issues, competition, and access to foreign markets.
    A coalition of interested parties (Ag Cooperatives, Rice Experiment Station, Richvale Irrigation District, land owners and rice seed growers, and the University of California) is being formed to launch an aggressive program to identify and control WWP in 2016. I request that CDFA delay the proposed classification of this potential weed pest, allowing the WWP control program to be implemented over the next two growing seasons. A concept draft proposal is included after the specific comments that follow.
    Specific Comments
    History & Status:
    Official Control: Butte County Agricultural Commissioner (BCAC) has only had limited and part time staff monitoring. There has been departure of staff and a transition to a new Agricultural Commissioner and details and extent of the control efforts are not clear and were certainly limited. No funded state program for weed control is available.
    California Distribution: Details on the distribution from the BCAC are being requested but need updating for 2015. Growers in the region have been watching for the WWP with the help of BCAC and private pest control advisors and treating, but the specifics and extent of that is unknown.

    Other range: In contacting a weed scientist colleague with Louisiana State University Agricultural Center about their experience with WWP. His email response was that it was easy to control with registered rice herbicides (especially Grandstand and ALS herbicides) and was not a weed that he gets a lot of questions about.

    Pest Dispersal Potential:
    I would submit that the potential for distribution in commercial seed is relatively low. RES varieties are grown on more than 90% of California’s rice acreage. All the new varieties are protected under the Plant Variety Protect Act Title V (must be grown as a class of certified seed). California Crop Improvement Association (official seed certifying agency) is very diligent and is not going to approve a seed field with
    WWP, and certified classes of seed are lab inspected for purity from weeds. In addition, the seeds are very small and would not likely make it through the harvester and seed cleaning process. Registered rice herbicides and contact herbicides are available and are effective control agents.

    Economic Impact:
    Although this pest in found in the Southern US, it is apparently easily controlled by registered herbicides in commercial rice production and not identified as a major weed pest. Major economic impact on yield, production costs, market loss, or normal cultural practices is not indicated. It is not a known vector, or injurious or poisonous to agriculturally important animals, interfering with water delivery, and thus the High Risk (3) rating should be reduced.

    Based on the considerations above (no yield/management impact, not transported in rice seed, available herbicides, and instigating broad based control program in the region) we request the Total Score be reduce to 11, placing it in the B category.

    Comprehensive Winged Water-Primrose Control Program:
    Beginning in January 2016 a series of meetings have been initiated among stakeholders and expanded to include more key groups to develop an aggressive program to address this weed pest. Understanding the efforts made by BCAC and others over the past years is still incomplete but is now starting to come together with genuine concern and conviction.

    Concept Draft Proposal
    Agencies, Organizations, Supporters Responsibility

    Butte County Agricultural Commissioner Regulatory, Oversight, Monitoring
    University of California
    Cooperative Extension Butte Co. Education and Outreach Approach
    UC Davis Rice Weed Science Biology, Control options
    Rice Experiment Station Support, grower outreach and treatment
    Butte County Rice Growers Association Support, grower outreach and treatment
    Richvale Irrigation District Monitoring, grower outreach and treatment
    Drainage Districts Monitoring, grower outreach and treatment
    Richvale Seed Growers & others Support, monitoring, outreach and treatment
    Rice growers in the region Support, monitoring, outreach and treatment
    California Crop Improvement Association Education, monitoring, outreach, scouting
    Butte County Farm Bureau Education and outreach
    Butte County Vector Control Scouting resource
    Identified Needs
    • Full time intern to scout, identify, record, and treat sites in cooperation with participants including confirmation of grower, land owner or agency treatment to begin in March through the fall.
    • Restrictions on equipment movement and or required cleaning of infected fields or sites.
    • Planting of only certified classes’ of rice seed
    • Identification of critical points of control and monitoring for control success and containment.
    • Demonstration of control of pest from infested areas
    • Funded multi-year effort

    Cc: L. Mendoza, BCAC
    C. Hoff, BUCRA
    S. Early, Richvale Irrigation District
    R.G. Mutters, UCCE Butte County
    T. Blank, California Crop Improvement Association
    CCRRF Board of Directors

    1. As required by Title 3, California Code of Regulations, section 3162 pest risk assessments follow a format with certain criteria; seed production is not among them. If the weed in question spreads further, it may impact seed production. Assigning a A rating to a Q rated plant should not affect seed production.

      Q rated pests are treated as if they are A rated in regulation. The proposed permanent rating of A should not affect regulation in this regard. As the seeds of winged water-primrose are much smaller than rice grains, there should be no problem in producing clean rice seed from lightly infested rice fields such as currently exist.

      The seed of this pest can be removed by cleaning seed. However, winged water-primrose may be spread by uncleaned seed. Even if this pathway were rated low risk as almost all seed is cleaned, this pest still has the ability to spread quickly via water, equipment, and even animals.

      The PPR states that “Risk is High (3) as the plant can lower crop yields, trigger quarantines, and force changes in cultural practices.”
      Risk analysis addresses potential as well as demonstrated risk. You state above that in fact this plant does potentially threaten markets. It has already changed cultural practices in infested areas. That it has not yet lowered crop yields is excellent news, but its known allelopathy and its behavior in other countries demonstrates a significant risk that it could do so if not controlled.

  5. Re: 3. Pest Dispersal Potential: It is unlikely that the dispersal potential is high. I disagree with the assumption that the weed was introduced into CA from a seed lot, thus making the score 2. Re: 4. Economic Impact: Thus far, there has been no proven impact on rice yield because of this pest; this pest has no foreseen indications of triggering a quarantine that could lead to the loss of markets, and our cultural practices in rice are already diversified, and there would be no change to which cultural practices couldn’t be adapted, thus making the score 1.
    Re: 5. Environmental Impact: Since the detection of this pest there has been no verifiable proof of significant environmental impact, thus making the score 1.

    Therefore, the final score would be more accurately stated to be 8, allowing the continued Pest Rating to remain Q.

    1. As required by Title 3, California Code of Regulations, section 3162 pest risk assessments follow a format with certain criteria; seed production is not among them. If the weed in question spreads further, it may impact seed production. Assigning a A rating to a Q rated plant should not affect seed production.

      The seed of this pest can be removed by cleaning seed. However, winged water-primrose may be spread by uncleaned seed. Even if this pathway were rated low risk as almost all seed is cleaned, because of the voluminous production of very small seed, this pest still has the ability to spread quickly via water, equipment, and even animals.

      The lettered list in the Proposed Pest Rating is a list of potential economic impacts. The PPR states that “Risk is High (3) as the plant can lower crop yields, trigger quarantines, and force changes in cultural practices.”
      Risk analysis addresses potential as well as demonstrated risk. This plant does potentially threaten markets. It has already changed cultural practices in infested areas. That it has not yet lowered crop yields is excellent news, but its known allelopathy and its behavior in other countries demonstrates a significant risk that it could do so if not controlled.

      New weeds of important commodities and of wetlands are generally viewed as high risk, even if a management plan exists to control or eradicate it. In fact, one major reason to rate a pest is to help regulate its movement into and through the state and to encourage control measures.

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