Biological control of invasive water primroses, Ludwigia spp., in the United States: A feasibility assessment

Authors: Reddy, Angelica; Pratt, Paul; Grewell, Brenda; HARMS, NATHAN - Us Army Engineer Research And Dvelopment Center; CABRERA WALSH, GUILLERMO - Fuedei; HERNANDEZ, CRISTINA - Fuedei; FALTLHAUSER, ANA - Fuedei; CIBILS-STEWART, XIMENA - National Institute Of Agropecuarian Technology (INTA)

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2020
Publication Date: 8/31/2021
Citation: Reddy, A.M., Pratt, P.D., Grewell, B.J., Harms, N.E., Cabrera Walsh, G., Hernandez, C., Faltlhauser, A., Cibils-Stewart, X. 2021. Biological control of invasive water primroses, Ludwigia spp., in the United States: A feasibility assessment. Journal of Aquatic Plant Management. 59s:67–77. https://apms.org/journal/.

Interpretive Summary: Exotic water primroses are aggressive invaders in both aquatic and riparian ecosystems worldwide. Ludwigia hexapetala, L. peploides subsp. peploides, L. peploides subsp. montevidensis, L. grandiflora, and L. decurrens have naturalized in aquatic ecosystems in the US and are the focus of this study. The only control tools available to resource managers for suppression of Ludwigia spp. are physical and chemical methods, but these options are often limited in effectiveness, and by costs and regulatory constraints. Biological control is an alternative that can be used alone or in combination with traditional methods. The purposes of this study are to explore the feasibility of a biological control program targeting problematic Ludwigia spp. in the US, and to propose a list of plant species for consideration during host range studies of candidate herbivores. A variety of native insects feed on Ludwigia spp. in the US, however, most are generalists and have no appreciable influence on plant growth or fitness. Foreign exploration for natural enemies of Ludwigia spp. in South America suggests that a rich herbivore fauna is associated with the plants in their native range. Candidate agents must have a section-level host specificity as several Ludwigia spp. are also native to the US. Therefore, the plant test list is designed to distinguish herbivore host ranges based on phylogenetic relationships of the test plants. For those Ludwigia spp. where eradication may no longer be possible because the weed is regionally abundant, biological control may be the primary control option when traditional methods are not feasible.

Technical Abstract: Exotic water primroses (Ludwigia spp.) are aggressive invaders in both aquatic and riparian ecosystems worldwide. Four Ludwigia taxa have naturalized in aquatic systems of the U.S.: Uruguayan primrose-willow (Ludwigia hexapetala), creeping water primrose (L. peploides subsp. peploides and L. peploides subsp. montevidensis), and large-flower primrose-willow (L. grandiflora). To date, the only weed control tools available to resource managers for suppression of Ludwigia spp. are physical and chemical methods, but these options are often limited by costs and regulatory constraints. Biological control, the introduction of host specific herbivores from the weed’s native range, is an additional management method. The purposes of this study are to explore the feasibility of a biological control program targeting exotic Ludwigia spp. in the U.S. and to propose a list of plant species for consideration during host range studies of candidate herbivores. A variety of native insects feed on Ludwigia spp. in the U.S., however, most are generalists and have no appreciable influence on plant growth or fitness. Foreign exploration for natural enemies of Ludwigia spp. in Argentina and Uruguay suggests that a rich herbivore fauna is associated with the plants in their native range. Candidate biological control agents must have a tribe-level host specificity as several Ludwigia spp. are also native to the U.S. Therefore, the proposed plant test list is designed to distinguish herbivore host ranges based on phylogenetic relationships of the test plants. For those Ludwigia spp. where eradication is no longer possible because the weed is regionally abundant, biological control may be the primary control option when traditional methods are not feasible.