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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** 2023 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 is for project 2030-22000-032-000D. 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). 

In support of Objective 1, progress was made to advance knowledge of weed biology and invasion ecology as a foundation for improved IWM strategies in aquatic ecosystems. Accurate taxonomic identification of weed species is the essential first step towards development of effective IWM strategies and supporting research. Native and alien lineages of common reed (Phragmites australis) co-occur, yet their distribution in northern California is largely unknown and taxonomic keys published elsewhere do not universally apply. Under Sub-objective 1A, ARS scientists at Davis, California, completed biochemical and microscopic morphological trait analyses of 400 leaf and inflorescence samples from 20 study populations. Scientists at Sidney, Montana, extracted genomic DNA from leaf samples, and used microsatellite markers and restriction site analysis to identify native or alien status as well as genotype of all samples. Genetic analyses will be finished during September 2023 and will clarify the taxonomic distribution and support targeted weed management in wetland restoration projects.

South American spongeplant (Limnobium laevigatum) is a noxious weed that has been introduced to California, likely through the nursery trade. To support Sub-objective 1B, ARS researchers at Davis, California, completed a second year of monthly phenological monitoring, and biomass and aquatic environmental data collection at three study sites invaded by spongeplant in the Sacramento-San Joaquin River Delta in northern California. Graphical summary and presentation of biomass allocation and environmental sampling results were completed. Statistical analyses of weed biomass and environmental data and a draft manuscript have been initiated to report findings in a scientific journal.
 
To support Sub-objective 1B, progress continued on research to evaluate growth and salinity tolerances of alligator weed (Alternanthera philoxeroides) that has invaded freshwater to brackish tidal wetlands in California’s Sacramento-San Joaquin Delta. Lab analyses of soil, water and plant tissue samples from the study of 25 population sites along an estuarine salinity gradient were completed this year. Following four years of drought, the Delta experienced record-breaking winter floods. Therefore, an additional year of field data collection was implemented this year to characterize the contrasting conditions. Lab analysis of plant tissue samples from two greenhouse experiments evaluating 33 functional trait responses to four levels of salinity from freshwater to marine conditions were completed. Trait responses included growth and biomass allocation, stem morphology, photosynthetic and biochemical responses in plant tissues. Notably, there was no mortality of any experimental plants including both free-floating and emergent growth forms of alligator weed in freshwater, mid- to high-brackish salinity at 12 parts per thousand (ppt) and 24 ppt, or in 36 ppt marine conditions though relative growth rate and biomass production declined with increasing salinity in all cases.  

Recent alligator weed invasion and its rapid expansion in northern California waterways has led to stakeholder requests for effective biological control and IWM option. To support Sub-objective 2A, research continued to investigate methods for improving biological control of aquatic weeds through the lens of environmental variation and IWM. Experiments to compare thermal limits of multiple alligator weed flea beetle (Agasicles hygrophila) populations culminated in the discovery that genotypes from the insect’s native range (Argentina) are better adapted to California as compared to populations already present in the United States. These data indicate that importing new insects from Argentina is more likely to result in successful establishment and control of the exotic weed in contrast to simply moving insects from the southern to the western United States. A journal article documenting these results was accepted for publication. An experiment to determine the host range of the Argentine population of the alligator weed flea beetle indicates that the insect will not attack native plant species and will be as environmentally safe as the current population already established in the southeastern United States. Additional research determined that the host range of a second species of flea beetle (Disonycha argentinensis) is too broad to be considered suitable for release in the United States.  

Progress continued to evaluate the ability of arundo biological control agents to establish and suppress arundo under variable plant water stress status through IWM frameworks in subtemperate watersheds of northern California. Under Sub-objective 2B, measurements of arundo at five sites in the Central Valley of California at which the arundo wasp (Tetramesa romana) is established after releases in 2017 showed that live biomass recovered to pre-biocontrol levels by the fall of 2022. Establishment was confirmed by measurements at two additional sites at which the wasp was released in 2019-2020. The density of the wasp - less than 1 per main shoot and 1 per 5 side shoots - was 10-fold less than previously observed in southern Texas where the wasps reduced biomass. The arundo armored scale was found 1 to 2 meters above ground on the bases of 2 percent (%) to 59% of side shoots, demonstrating establishment. Sampling of post-herbicide regrowth at 3 sites in the Sacramento-San Joaquin Delta indicated 3- to 20-fold higher wasp density in regrowth than in old biocontrol plots, showing that chemical and biological control can be integrated. Sampling of arundo leaf sheaths was completed at 12 sites in California to characterize their fungal community by culturing and DNA extraction in preparation for sequencing. The arundo leafminer Lasioptera donacis, which feeds on sheaths, was imported from Italy and reared in quarantine.

Under Objective 3, ARS scientists at Davis, California, continued a study in Laguna de Santa Rosa wetlands invaded by Uruguayan primrose-willow (Ludwigia hexapetala) to evaluate plant species and ecological attributes that may provide biotic resistance to invasion for improved restoration and management outcomes. Results from analysis of 2022 field data suggested a need to expand 2023 sampling to add important relevant data. Eight replicate areas dominated by large clonal plant stands with varying levels of invader and native plant abundance were identified for additional transect sampling. Extreme flooding at study sites occurred in winter, delaying planned April- July data collection. Repeat visits to four wetland study areas and the added clonal cattail patches with varying levels of invader and native plant abundance were visited spring- summer. Deep and standing water boundaries were mapped to monitor drawdown for comparison with river water stage measured near the wetlands, and to determine when seasonal data collection could begin. Deep water persisted over parts of study areas into August. As drawdown commenced, seasonal plant and soil sampling, and environmental measurements were completed. Transect and plot sampling in areas with greater depth and duration of flooding will continue through fall for delayed completion of datasets for evaluation of the identity and degree to which native plant species and ecological attributes may provide biotic resistance to the primrose-willow invasion.

Supporting Objective 3, ARS researchers at Davis, California, and scientists at the University of Seville, Spain, collaborated in a subordinate project focused on reducing the impact of invasive yellow flag iris (Iris pseudacorus) in Pacific coast estuaries. Results from analyses of environmental variables and traits of I. pseudacorus recorded at population sites along estuarine gradients in the native (Guadalquivir Estuary) and invaded (San Francisco Bay-Delta Estuary) revealed that functional trait differences of alien iris populations in California have greater adaptive capacity to adjust to environmental stresses imposed by rising sea level with climate change than the native populations. Results refuted conventional wisdom that the species is limited to freshwater, and thereby improve risk assessments. Results were published in the journal Diversity and Distributions and a photograph from the study was featured on the journal’s cover. Progress was made on new analyses to identify indicator species that persist within the iris-invaded communities, and to evaluate species associations by functional groups and key plant traits for continuing research to improve weed and restoration management strategies. **Accomplishments** **Review Publications**
                            *DaSilva, A., Reddy, A.M., Pratt, P.D., Hansel Friedman, M.S., Grewell, B.J., Harms, N.E., Cibils-Stewart, X., Cabrera Walsh, G., Faltlhauser, A., Chamorro, M.L. 2022. Biology of immature stages and host range characteristics of Sudauleutes bosqi (Coleoptera: Curculionidae), a candidate biological control agent of exotic Ludwigia spp. in the USA. Florida Entomologist. 105(3):243-249. https://doi.org/10.1653/024.105.0310.*
                                *Conrad, J.L., Thomas, M., Jetter, K., Madsen, J.D., Pratt, P.D., Moran, P.J., Takekawa, J., Darin, G.S., Kenison, L. 2023. Invasive aquatic vegetation in the Sacramento-San Joaquin Delta and Suisun Marsh: The history and science of control efforts and recommendations for the path forward. San Francisco Estuary and Watershed Science.  20(4). Article 4. https://doi.org/10.15447/sfews.2023v20iss4art4.*
                                *Castillo, J.M., Gallego-Tevar, B., Grewell, B.J. 2023. Wrack burial limits germination and establishment of yellow flag iris (Iris pseudacorus L.). Plants. 12(7). Article 1510. https://doi.org/10.3390/plants12071510.*
                                *Infante-Izquierdo, M.D., Romero-Martin, R., Castillo, J.M., Grewell, B.J., Soriano, J.J., Nieva, F.J., Munoz-Rodriguez, A.F. 2023. Seed viability, spikelet dispersal, seed banks and seed storage requirements for native and invasive cordgrasses (genus Spartina) in Southwest Iberian Peninsula. Wetlands. 43. Article 8. https://doi.org/10.1007/s13157-022-01655-2.*
                                *Grewell, B.J., Gallego-Tevar, B., Barcenas-Moreno, G., Whitcraft, C.R., Thorne, K.M., Buffington, K.J., Castillo, J.M. 2023. Phenotypic trait differences between Iris pseudacorus in native and introduced ranges support greater capacity of invasive populations to withstand sea level rise. Diversity and Distributions. 29(7):834-848. https://doi.org/10.1111/ddi.13694.*
                                *Moran, P.J., Miskella Jr., J.J., Morgan, C.M., Madsen, J.D. 2023. Toxicity of herbicides used for control of waterhyacinth in the California Delta towards the planthopper Megamelus scutellaris released for biological control. Biocontrol Science and Technology. 33(5): 448-466. https://doi.org/10.1080/09583157.2023.2196707.*
                                *Young, S.L., Campbell, J.W., Fulcher, M.R., Grewell, B.J. 2023. Climate and pest interactions pose a cross-landscape management challenge to soil and water conservation. Journal of Soil and Water Conservation. 78(2):39A-44A. https://doi.org/10.2489/jswc.2023.1025A.*


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