Tag Archives: Ludwigia decurrens

Ludwigia decurrens (winged water-primrose)

California Pest Rating for
Ludwigia decurrens (winged water-primrose)
Myrtales; Onagraceae
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)


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.


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.

Pest Rating:  A  |  Proposed Seed Rating:  P

Posted by ls