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ARS Home Pacific West Area Albany, California Western Regional Research Center Invasive Species and Pollinator Health Research





- Grewell, Brenda
- Pratt, Paul
- Moran, Patrick
- Mueller, Rebecca
- 2023
- 2022
- 2021
- Publications
- Crop Protection & Quarantine (304)

Research Project: Integrated Weed Management and Restoration Strategies to Protect Water Resources and Aquatic and Wetland Ecosystems of the Far Western U.S. **Location:
                            Invasive Species and Pollinator Health** 2021 Annual Report **Objectives**
                                

The long-term objective of this project is to develop and improve integrated weed management (IWM) and restoration strategies that successfully reduce the abundance of invasive aquatic and wetland weeds, to aid in the protection of water resources and improve environmental quality in aquatic and wetland ecosystems in far western states. This holistic approach, applied through an IWM framework, will increase the efficacy of weed management and reduce weed abundance to restore invasion-resistant vegetation and ecosystem services. Specific objectives to be addressed follow. 

Objective 1: Advance basic knowledge of weed biology and invasion ecology and develop improved integrated weed management (IWM) strategies in aquatic and wetland ecosystems. 

Sub-objective 1A: Determine the correct taxonomy, systematics and extent of hybridization of invasive weeds. 

Sub-objective 1B: Identify key biological and ecological processes influencing growth, invasiveness and IWM of aquatic and wetland weeds. 

Sub-objective 1C: Evaluate new herbicides and improve herbicide application techniques to enhance management efficacy of aquatic weed species. 

Objective 2: Evaluate the contributions of biological control on aquatic weed population dynamics through the lens of environmental variation, IWM, and ecosystem management. 

Sub-objective 2A: Evaluate biological, demographic and ecological factors that affect insect biological control agents, herbivory and weed abundance to improve efficacy of biological control. 

Sub-objective 2B: Evaluate impact of biological control of invasive wetland and riparian weeds in the context of integrated weed management. 

Objective 3: Develop ecological restoration implementation and monitoring strategies within an IWM framework to overcome invasive plant impacts and achieve restoration of plant communities and ecosystem services. 

Sub-objective 3A: Determine plant community and environmental characteristics that contribute to invasion resistance. **Approach**
                                

To support Objective 1, field sampling and molecular tools will be used to confirm genotypes of native and alien Phragmites australis and hybrids to elucidate genetic identity and diagnostic morphological traits of invasive taxa specific to the Delta-Suisun Marsh. In a 2-year field study at 3 Delta study sites, we will evaluate phenological development, biomass production and growth rates of South American spongeplant monthly to determine optimal timing of management. In a greenhouse experiment, we will also assess growth of 5 invasive and 3 native aquatic weed species in response to 6 water temperatures to develop predictive models to identify optimal timing for herbicide application. We will field measure plant traits and acclimation of alligator weed along a tidal range and salinity gradient. In a greenhouse, we will evaluate salinity tolerance of alligator weed using 2 growth forms (floating, emergent) X 4 salinity levels X 6 replicates arranged in a nested random block design. Experimental screening tests of new herbicide active ingredients will be conducted under controlled conditions using a hood-enclosed spray table and jar trials. Effective herbicides will then be tested in large replicated outdoor mesocosm experiments to assess weed survival and biomass responses. Dye studies will be performed at replicated Delta sites with low, medium and high water residence times to determine efficacy, optimal concentrations and exposure times of new herbicides to improve management of submersed aquatic plant species. 

Under Objective 2, alligator weed biological control agents (A. hygrophila and A. andersoni) will be acquired from domestic and foreign sources. Experiments in controlled temperature incubators will elucidate critical minimum thermal limits and interspecific differences in cold tolerance to discover climatically-compatible biotypes for establishment, over-wintering, and efficacy for IWM in western watersheds. The effect of plant water availability on the establishment and impact of biological control for IWM of arundo will be studied. We hypothesize releases of arundo wasp and arundo armored scale will establish larger populations in release plots with integration of mechanical control than in plots with no pre-treatment. Pre-dawn water potential measurements of plant water status will be correlated with arundo wasp exit hole counts at 50 points across 3 sites. Colonization and impact of both insects on regrowth of arundo following herbicide application will be assessed. 

Under Objective 3, we will design revegetation techniques using biotic resistance in an IWM framework to overcome invasive water primrose impacts in wetlands. Plant community composition, species abundance, and environmental variables will be assessed in large replicated field plots. Indicator species analysis, trait–environment filter models, and experiments will be used to identify strongly persistent native plant species resistant to competitive displacement by the invader under varying environmental conditions. Results will provide a foundation for IWM using improved restoration techniques to reduce invader impacts. **Progress Report**
                                

This progress report for project 2030-22300-032-00D replaces expired projects 2030-22000-029-00D and 2030-22000-030-00D. See the final reports of the former projects for additional information. The goal of this project is to decrease the abundance of aquatic weeds in far western states by increasing the efficacy of biologically-based integrative weed management (IWM). 

Accurate taxonomic identification of weed species is a critical first step for development of effective IWM strategies. Native and alien lineages of Phragmites australis (common reed) co-occur in North America, both have recently been recognized in California, yet identification and their distribution in northern California is unknown. Under Sub-objective 1A, ARS scientists at Davis, California, secured access permits and established 20 study sites to determine the correct taxonomy and systematics with focus on areas to support weed management in large-scale wetland restoration projects. Specimens of common reed were collected and evaluated to refine sampling plans for genetic study, and to define methods for measurement of key plant traits and habitat conditions. 

For Sub-objective 1B, studies were initiated to identify key processes influencing growth and invasiveness of submersed and floating aquatic weeds. Study sites were selected in the Sacramento-San Joaquin Delta to improve understanding of the phenology and life history characteristics of South American spongeplant. Regulatory permits were obtained to sample and retain this Class A noxious weed in California, and summer sampling and biomass analyses were conducted. Under Sub-objective 1B, greenhouse studies were also planned to evaluate water temperature as a predictor of growth initiation and sprouting to inform optimal timing of management for floating aquatic weeds. These studies require plant propagules in winter quiescence state at the start of experiments. Maximized telework and work site capacity restrictions prohibited our ability to start the trials during the critical time for collection of propagules, and pandemic restrictions also precluded the daily staff attention that is essential to maintain the experiments. The next possible time for quiescent propagule collection and study initiation is in the upcoming winter season; therefore this effort has been rescheduled for fiscal year (FY) 2022. 

Outbreaking populations of Alternanthera philoxeroides (alligator weed), an aggressive aquatic weed, have recently established in northern California. Supporting Objective 1, scientists at Davis and Albany, California, and collaborators, published a journal article reporting genetic analyses of 90 alligator weed populations sampled throughout the United States. Seven haplotypes and high genetic diversity were discovered. These genetic findings provide a foundation for evaluation of haplotype differences in invasiveness, and susceptibility to herbicides and herbivory to support biological control and IWM strategies.

Alligator weed has recently invaded the San Francisco-Bay Delta Estuary, where populations are spreading from freshwater into brackish habitats, though the species was previously considered intolerant of salinity. Scientists in Davis and Albany, California, initiated research to evaluate growth and salinity tolerances of genotypes under local climate and estuarine habitats affected by sea level rise. The team mapped 62 population patches along a salinity gradient from which 25 randomly selected study sites were established. Collection of samples for assessment of percent plant cover, canopy structure, biomass, leaf area, and tissue chemistry commenced, along with soil cores and water samples for analyses. In situ water quality measurements were recorded at slack high tidal stage. Data are being used to inform treatments for a greenhouse experiment to investigate alligator weed growth and chemistry in response to salinity levels.  

Under Sub-objective 1C, we initiated efforts to bring a new generation of herbicides to enhance IWM strategies for aquatic weeds. A draft white paper on the identification and attributes of potential new herbicides for use in aquatic sites was completed this year, and review by other experts on herbicides has been initiated. We surveyed and selected ten study sites in the Sacramento-San Joaquin Delta for dye studies to determine residence times and herbicide concentrations for site specific environmental conditions. We also selected two sites for a demonstration project for the use of bubble curtains to improve herbicide application methods and enhance the effectiveness of herbicides for IWM of submersed aquatic weeds. 

To support Objective 2, new studies were initiated to evaluate the contributions of biological control on aquatic weed population dynamics through the lens of environmental variation and IWM. Alligator weed is successfully controlled in the southern United States by a flea beetle, thrips, and a moth, but these same insects have been unsuccessful in more northerly distributions of the weed, including California. An option for improving control of this weed in its northern range is identifying cold-hardy populations of the insects that are effectively controlling the weed in southern climates. Under Sub-objective 2A, ARS scientists acquired two populations of the alligator weed flea beetle from northern Florida and Louisiana as well as two populations from the insect’s native range in Uruguay and Argentina. Similarly, populations of alligator weed thrips were obtained from Mississippi, North Carolina, Argentina, and Uruguay. These populations were colonized and maintained in the laboratory (for U.S.-collected populations) or containment facility (for foreign-collected populations). Experiments are underway to compare the thermal limits of these insect populations, to understand their suitability for release in California and other locations where the insects are currently underperforming. A journal article establishing a general framework to address climate incompatibility among weed and biological control agents was published.  

Under Sub-objective 2B, surveys of releases of the shoot-galling arundo wasp and root-feeding arundo armored scale verified the presence of the wasp at one site in the southern San Joaquin River watershed and one in the northern Sacramento River watershed; at least 75% of points surveyed had galls. Sparse wasp populations were found at one site in the Sacramento-San Joaquin Delta. At two additional sites, plot pre-cutting (mowing at 6 ft height), followed by release of 1,572 wasps, led to 4.8-fold elevated wasp abundance. The arundo armored scale was sampled by digging up rhizome (root) samples, and it was confirmed as established at seven sites, covering both watersheds and the Delta. Additional scales were released in late 2020 at a site that has large wasp populations, for future combined impact measurement. Dissections showed that similar releases in 2019 at two sites were successful. Herbicide was applied to arundo outside of biological control plots by collaborators at one site in the Delta for future measurement of colonization of regrowth.

Objective 3 addresses ecological restoration implementation and monitoring strategies within an IWM framework to overcome invasive plant impacts and achieve restoration of plant communities and ecosystem services. Under Objective 3, scientists at Davis, California, initiated a new study to determine plant community and environmental characteristics that contribute to invasion resistance. Potential study sites were explored, and a large site that includes a range of wetland types invaded by the aquatic weed Uruguayan primrose-willow (Ludwigia hexapetala) was selected for field research. A literature review was updated, and project collaborators refined study designs and methods to determine the degree to which native plant species and ecological attributes may provide biotic resistance to invasions in a restoration context. **Accomplishments** **Review Publications**
                            *Abbas, A.M., Pickart, A.J., Goldsmith, L.M., Davenport, D.N., Newby, B., Munoz-Rodriguez, A.F., Grewell, B.J., Castillo, J.M. 2021. Seed bank persistence of a South American cordgrass in invaded northern Atlantic and Pacific Coast estuaries. AoB Plants. 13:2. https://doi.org/10.1093/aobpla/plab014.*
                                *Gillard, M.B., Castillo, J.M., Mesgaran, M.B., Futrell, C.J., Grewell, B.J. 2021. High aqueous salinity does not preclude germination of invasive Iris pseudacorus from estuarine populations. Ecosphere. 12(5). Article e03486. https://doi.org/10.1002/ecs2.3486.*
                                *Hopper, J.V., Pratt, P.D., Reddy, A.M., McCue, K.F., Rivas, S.O., Grosholz, E.D. 2020. Abiotic and biotic influences on the performance of two biological control agents, Neochetina bruchi and N. eichhorniae, in the Sacramento-San Joaquin River Delta, California (USA). Biological Control. 153. Article 104495. https://doi.org/10.1016/j.biocontrol.2020.104495.*
                                *Rayamajhi, M.B., Rohrig, E., Lake, E.C., Smith, M., Pratt, P.D., Dray Jr, F.A., Halbritter, D.A., Leidi, J.G. 2021. Phenological synchrony between a weed (Dioscorea bulbifera) and a biocontrol agent (Lilioceris cheni) in the introduced range, Florida: implication in biological control. Biocontrol Science and Technology. 31(8):797–816. https://doi.org/10.1080/09583157.2021.1885627.*
                                *Gaskin, J.F., Andreas, J., Grewell, B.J., Haefliger, P., Harms, N.E. 2021. Diversity and origins of Butomus umbellatus (flowering rush) invasion in North America. Aquatic Botany. 173:103400. https://doi.org/10.1016/j.aquabot.2021.103400.*
                                *Reddy, A.M., Pratt, P.D., Grewell, B.J., Harms, N.E., Cibils-Stewart, X., Cabrera Walsh, G., Faltlhauser, A. 2021. Biological and host range characteristics of Lysathia flavipes (Coleoptera: Chrysomelidae), a candidate biological control agent of invasive Ludwigia spp. (Onagraceae) in the USA. Insects. 12(5):471. https://doi.org/10.3390/insects12050471.*
                                *Grewell, B.J., Gallego-Tevar, B., Gillard, M.B., Futrell, C.J., Reicholf, R., Castillo, J.M. 2021. Salinity and inundation effects on Iris pseudacorus: implications for tidal wetland invasion with sea level rise. Plant and Soil. https://doi.org/10.1007/s11104-021-04997-8.*
                                *Infante-Izquierdo, M.D., Munoz-Rodriguez, A.F., Nieva, F.J., Polo-Avila, A., Sanchez-Gullon, E., Soriano, J.J., Sanjose, I., Grewell, B.J., Castillo, J.M. 2021. Variation in sexual reproductive output among exotic taxa of Spartina (Poaceae). Aquatic Ecology. 55:107-123. https://doi.org/10.1007/s10452-020-09815-4.*


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