Location: Invasive Species and Pollinator Health
2024 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
The goal of this project (2030-22300-032-000D) is to decrease the abundance of aquatic weeds in western states by increasing the efficacy of biologically-based integrated weed management (IWM).
Accurate taxonomic identification of weed species is a critical foundation for the development of effective IWM strategies. Distribution of native vs. alien lineages of common reed (Phragmites australis) intensively studied elsewhere were unknown in northern California, creating uncertainty for management. In support of Sub-objective 1A, results of genetic analyses were compared with biochemical and morphological traits from 400 plant samples collected at 20 populations in the San Francisco Bay-Delta Estuary. Overall, 42% of plants sampled were native, and 57% were the alien taxa. Populations in the inland Delta were largely native (96%), while 62% of down-estuary populations included the exotic taxa. Aliens were most often in diked wetlands and recent breached-levee restoration sites with hydrologic disturbance. Phenological research and trait analyses are underway to develop observation-based identification tools to support targeted management of the highly invasive non-native weed, tidal marsh restoration, and conservation of greater biological diversity associated with native Phragmites australis subspecies americanus.
Research efforts continued towards identifying key biological and ecological processes influencing the growth, invasiveness, and IWM of aquatic weeds. South American spongeplant (Limnobium laevigatum) is a noxious weed that has been introduced to California, likely through the nursery trade. In support of Sub-objective 1B, two years of data collection were performed at three study sites in the Sacramento-San Joaquin River Delta. Following retirement of the former investigator, a new Research Ecologist assumed leadership of research to determine the phenology and life history of this weed as a basis for improved management. Following field visits to study sites and review of data, statistical analysis of phenological monitoring, biomass allocation, and aquatic environmental data were performed. Progress was made on a draft manuscript to be submitted for publication in a scientific journal.
In support of Sub-objective 1B, field research and analysis of greenhouse experiments continued to assess salinity tolerance and invasive spread of alligator weed (Alternanthera philoxeroides) invading tidal wetlands in California's Sacramento-San Joaquin Delta. An additional year of field data collection was completed to evaluate environmental conditions relative to steady annual increases in the spread and abundance of the weed despite interannual environmental differences. Final data analyses will be performed after fall data collection this year, when the weed achieves peak biomass production at study sites. Analyses of data from two greenhouse experiments evaluating emergent and free-floating growth forms of alligator weed to four estuarine salinity levels were completed. Results document the weed’s sensitivity to salinity stress yet revealed plant trait responses supporting dual tolerance and stress escape strategies. A manuscript reporting experimental results is nearly complete for submittal to a scientific journal.
A new scientist at Davis, California, assumed leadership of studies to evaluate new and efficacious herbicides and improved application methods to support IWM of aquatic weeds. In support of Sub-objective 1C, ribbon weed (Vallisneria australis) and alligator weed were propagated for plants to test the efficacy of submersed and foliar herbicide applications and the timing of their applications to improve management efforts in California and elsewhere in the United States where aquatic ecosystems are impacted by these invasive plant species.
Concentration exposure time is pivotal to efficacious and selective herbicide control of aquatic invasive plant species, yet herbicide exposure times due to application techniques have often been inadequate. The Sacramento-San Joaquin Delta (Delta) is a mixed semi-diurnal tidal system, with two low and two high tides of unequal heights and changes in flow every 25 hours, complicating achievement of adequate weed exposures to aquatic herbicides. Improved timing of foliar applications on submersed aquatic weeds promoting adequate exposure may improve weed control and reduce herbicide inputs. In support of Sub-objective 1C, an initial dye study was performed, and others are planned to identify the impact of treatment timing relative to location-specific tidal regimes and to determine how tidal influx affects water and herbicide retention times. In addition, deployment of bubble curtain technology at Delta sites will be underway by year’s end to evaluate whether they can improve herbicide concentration exposure time in tidewater areas with invasive submersed aquatic plant species.
The invasion of alligator weed in California has led to stakeholder requests for effective management tools for this exotic aquatic plant. In support Objective 2, research on improving biological control of alligator weed included experiments to compare thermal limits of multiple alligator weed flea beetle (Agasicles hygrophila) populations. These studies led to 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. Additional research revealed that the host range of the Argentine biotype of the flea beetle is limited to the target weed, with larvae failing to complete development on all other plants tested. These data indicate that importing new insects from Argentina is more likely to result in safe and successful control of the exotic weed in contrast to simply moving insects from the southern to the western United States. A release petition was submitted to the federal regulatory agency for the release of this new biotype in California and a journal article documenting the flea beetle’s host range was also submitted for publication.
Arundo (Arundo donax) is an invasive giant grass that consumes water and impedes water flow to growers. In additional support of Objective 2, the armored scale Rhizaspidiotus donacis was confirmed as established at nine sites in the Central Valley of northern California by sampling arundo side shoots six years after release. At least one adult female was found on 25% of nodes. A total of 4,276 females produced 42,093 live ‘crawlers’ (offspring) in the lab, or about 10 per female, showing that reproductive females are in the field. The scale dispersed up to 73 m from release plots, with dispersal distance averaging 10 m, or about 2 m per year. No prior study had examined both establishment and post-release dispersal of this insect. Two species in the fungal genus Fusarium, which can act as both generalist decomposers and as plant pathogens, were identified as the primary fungal occupants of leaf sheaths of arundo collected at nine California field sites. F. fujikuroi and F. langsethiae were identified through culturing, DNA extraction and sequencing of the full-length internal transcribed spacer region and partial sequencing of the large subunit ribosomal region. Both Fusarium species were recovered from leaf sheaths infested with the arundo leafminer Lasioptera donacis after rearing an Italian population of the leafminer in quarantine using a novel method that exposed adult females to sporulating cultures. This result suggests that female leafminers can acquire the California fungi and subsequently infect arundo plants when they lay their eggs, providing part of the food source for larvae.
For Objective 3, research continued in Laguna de Santa Rosa wetlands invaded by Uruguayan primrose-willow (Ludwigia hexapetala) to evaluate plant species that may provide biotic resistance to invasion in a restoration context. Data collection previously delayed due to deep persistent flooding was completed this year. Point-intercept sampling of 64 transects to assess plant species presence and cover were completed in large vegetation monitoring plots stratified by hydrological subarea and presence/absence of L. hexapetala. Soil cores (n=64) were collected and analyzed in the laboratory for physico-chemical characteristics. Annual mapping of the distribution of L. hexapetala and five clonal macrophyte species to assess interannual changes was completed. Analyses to identify species-environment associations, and indicator species that persist within Ludwigia-invaded communities were initiated to support design of experimental tests of biotic resistance potential for augmentative restoration plantings.
Accomplishments
1. Arundo armored scale established and dispersing in the Central Valley of California. Arundo is a giant non-native, invasive grass that consumes water, obstructs water flow and flood control systems, fuels wildfires and displaces native species. An ARS scientist in Albany, California, documented establishment and dispersal of a biological control agent, an armored scale (Rhizaspidiotus donacis) released by ARS in 2017 in the Central Valley of northern California. Over 1,700 arundo side shoots were collected across nine armored scale release sites and examined in the field and lab, and 25% of them had at least one adult female. A total of 4,300 females were isolated and produced an average of 10 offspring per female in the lab, demonstrating establishment of reproductive populations. Scales dispersed an average of 10 m from the release plots, or about 2 m per year, but at one site scales dispersed 73 m. This is the most comprehensive study of establishment and the first study of field dispersal of R. donacis, which is the first armored scale in the world to be used as a biological weed control agent. The results are informing recommendations for scientists and natural resource managers in the United States and internationally.
Review Publications
Sánchez-Restrepo, A.F., Reche, V.A., Cabrera, N., Pan, X., Pratt, P.D., Sosa, A. 2023. What distribution models of alligator weed in its native and invaded ranges tell us about its invasion story and biological control. Entomologia Experimentalis et Applicata. 171(12):1009–1018. https://doi.org/10.1111/eea.13353.
Bitume, E.V., Rogers, V.D., Pratt, P.D., Goolsby, J., Moran, P.J. 2024. Establishment of the wasp Tetramesa romana for biological control of Arundo donax in northern California and the role of release plot manipulation. Biological Control. 192. Article 105489. https://doi.org/10.1016/j.biocontrol.2024.105489.
Young, S.L., Anderson, J.V., Baerson, S.R., Bajsa Hirschel, J.N., Blumenthal, D.M., Boyd, C.S., Boyette, C.D., Brennan, E.B., Cantrell, C.L., Chao, W.S., Chee Sanford, J.C., Clements, D.D., Dray Jr, F.A., Duke, S.O., Porter, K.M., Fletcher, R.S., Fulcher, M.R., Gaskin, J., Grewell, B.J., Hamerlynck, E.P., Hoagland, R.E., Horvath, D.P., Law, E.P., Madsen, J., Martin, D.E., Mattox, C.M., Mirsky, S.B., Molin, W.T., Moran, P.J., Mueller, R.C., Nandula, V.K., Newingham, B.A., Pan, Z., Porensky, L.M., Pratt, P.D., Price, A.J., Rector, B.G., Reddy, K.N., Sheley, R.L., Smith, L., Smith, M., Snyder, K.A., Tancos, M.A., West, N.M., Wheeler, G.S., Williams, M., Wolf, J.E., Wonkka, C.L., Wright, A.A., Xi, J., Ziska, L.H. 2023. Agricultural Research Service weed science research: past, present, and future. Weed Science. 71(4):312-327. https://doi.org/10.1017/wsc.2023.31.
Gallego-Tevar, B., Grewell, B.J., Gaskin, J.F., Castillo, J.M. 2024. Genetic and phenotypic differentiation in functional traits of Iris pseudacorus L. in native and introduced Mediterranean climate ranges. Biological Invasions. 26:2869-2882. https://doi.org/10.1007/s10530-024-03350-1.
Knight, I., Harms, N.E., Reddy, A.M., Pratt, P.D. 2023. Multivariate evaluation of cold tolerance in domestic and foreign populations for addressing climate mismatch in biological control of Alternanthera philoxeroides in the USA. Entomologia Experimentalis et Applicata. 171(12):1019-1033. https://doi.org/10.1111/eea.13301.