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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** 2022 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). 

Native and alien lineages of common reed (Phragmites australis) co-occur, yet their distribution in northern California is largely unknown. Under Sub-objective 1A, scientists in Davis, California, collected leaf tissue from 20 plants in each of 20 study populations for genetic, biochemical, and leaf trait analyses. Phenological development of study populations was monitored; measurements of morphological and biochemical traits, stem density and plant community composition within stands were measured; and voucher specimens were collected and archived for microscopic evaluations in the laboratory. Analyses of these data are underway to 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. For continuation of Sub-objective 1.B.1., three study sites in the Sacramento-San Joaquin River Delta in northern California were selected that have abundant growth of South American spongeplant. Researchers at Davis, California, continued collecting monthly phenological and life history information, and monthly biomass samples within all study populations. By the end of this calendar year, the field data collection will be complete.

Under Sub-objective 1.B.2, researchers at Davis, California, completed water temperature growth studies for Egeria (Egeria densa) and Eurasian watermilfoil (Myriophyllum spicatum). These studies were conducted under controlled water temperatures. The purpose of these studies is to create a temperature model that will use water temperature data to indicate when plant growth is initiated in a particular location. These results can be used to trigger timing of biologically-based management activities as an improvement over management operations based solely on time of year.

To support Objective 2, scientists in Davis and Albany, California, continued research to evaluate growth and salinity tolerances of alligator weed (Alternanthera philoxeroides) that has invaded the Sacramento-San Joaquin Delta, with brackish tidal habitats. Lab analyses of soil, water and plant tissue samples from 25 study population sites along an estuarine salinity gradient were completed this year. Shoots were propagated for experiments. Two greenhouse experiments were conducted to assess survival, growth, physiological and biochemical responses of two alligator weed growth forms in freshwater to marine salinity concentrations. Harvested samples were archived for laboratory analyses, and new experiments were designed to support improved weed risk assessments and biological control.  

For Sub-objective 1.C.1., researchers in Davis, California, examined new herbicides for controlling aquatic weeds in the Sacramento-San Joaquin Delta, and screened herbicides on new weed species. Experiments were initiated in small-scale mesocosms to screen aquatic herbicides for treatment of the recent invader Australian ribbonweed (Vallisneria australis), which has a proposed noxious weed rating under review by the State of California. Currently, there is no data on herbicide efficacy for this outbreaking weed species in the United States, so the purpose is to provide management tools for this weed. Evaluation was initiated on both liquid and granular formulations of the dipotassium salt of endothall, carfentrazone, complexed copper, diquat, the dimethylamine salt of endothall, flumioxazin, fluridone, imazamox, penoxsulam, and the recent herbicide florpyrauxifen-benzyl. 

Under Sub-objective 1.C.2., studies were reordered to accommodate work restrictions. Planned dye studies to support aquatic herbicide use in tidal field sites were delayed. In lieu of those studies, researchers in Davis, California, pursued small-scale studies. In the first, the concentration and exposure time relationship of diquat on Eurasian watermilfoil and egeria were evaluated. Diquat is a fast-acting aquatic herbicide that requires only a short contact time. Exposure times of 0.5, 1, 3, 6 and 12 hours were examined at diquat concentrations of 90 and 190 μl-1. Diquat may be a primary herbicide tool for controlling aquatic weeds in higher water exchange areas, and a combination of this information with water exchange information from dye studies will aid in selecting the appropriate herbicide tool. Tidal dye studies to assess aquatic herbicide movement will be initiated later this calendar year. 

To support Sub-objective 2A, scientists in Albany, California, conducted studies to assess options for improving biological control of alligator weed in its northern range by identifying cold-hardy populations of the insects that are effectively controlling the weed in southern climates. Populations of the alligator weed flea beetle from northern Florida and Louisiana, and from the insect’s native range in Uruguay and Argentina, were acquired. Similarly, populations of alligator weed thrips were obtained from Mississippi, North Carolina, Argentina, and Uruguay. In the containment facility, experiments were initiated to compare the thermal limits of these insect populations to aid in determining if one or more of the populations are suitable for release in northern California and other locations where biological control insects have underperformed. Studies to quantify development rate and survival indicate that the Argentina population of the flea beetle is better adapted to cooler conditions as compared to the other three populations. Lower and upper temperature limits on the beetle’s survival were not as informative as developmental studies. Additional research in support of Sub-objective 2A focused on determining the risk these introduced insects may have on fish when feeding on the biological control agents. Initial data indicate that rainbow trout and Delta smelt do not readily eat the flea beetle and prefer to reject the insect as prey. Fish feeding studies using the thrips are currently underway. Additionally, ARS scientists are conducting host range testing of a second species of flea beetle (Disonycha argentinensis) to determine if the insect may be suitable for release in the United States to complement existing biological control options. 

Under Sub-objective 2B, surveys at 11 sites in the Sacramento-San Joaquin River watersheds and Delta confirmed establishment of the shoot tip-galling arundo wasp at seven sites invaded by the giant grass, arundo (Arundo donax). At two sites, new release of the wasp after arundo cutting followed by mowing of regrowth increased wasp abundance 19-fold compared to plots that were ground-cut only. Shoot density and biomass were determined in 29 plots at study sites to measure wasp impact five years post-release. At one site, wasps dispersed 6.4 km. Seven plots each were cut to ground level, topped, or left uncut to allow colonization. Initial measurements were taken to examine drought stress in relation to wasp density. At one site in the Delta, wasp density was higher in post-herbicide regrowth than in older arundo protected from herbicides. Diseased leaves were used to culture fungi for DNA extraction to sequence the large subunit ribosomal RNA region and conduct whole-genome sequencing for the fungus used by the arundo leafminer, a prospective biological control agent.  

Under Objective 3, scientists in Davis, California, continued a study to determine plant community and environmental characteristics that contribute to invasion resistance. Vegetation monitoring transects and plots were established in the Laguna de Santa Rosa, which includes wetland environments invaded by the aquatic weed Uruguayan primrose-willow (Ludwigia hexapetala). Data on plant species presence and abundance, community composition, and environmental conditions were collected to establish an initial pre-restoration dataset. **Accomplishments** **Review Publications**
                            *Gallego-Tevar, B., Grewell, B.J., Whitcraft, C.R., Futrell, C.J., Barcenas-Moreno, G., Castillo, J.M. 2022. Contrasted impacts of yellow flag iris (Iris pseudacorus) on plant diversity in tidal wetlands within its native and invaded distribution ranges. Diversity. 14(5). Article 326. https://doi.org/10.3390/d14050326.*
                                *Wang, R., Chen, H., Bubenheim, D., Moran, P.J., Zhang, M. 2021. Modeling nitrogen runoff from Sacramento and San Joaquin river basins to Bay Delta Estuary: Current status and ecological implications. Journal of Aquatic Plant Management. 59s:107-111. https://apms.org/journal/.*
                                *Moran, P.J., Madsen, J.D., Pratt, P.D., Bubenheim, D.L., Hard, E., Jabusch, T., Carruthers, R.I. 2021. An overview of the Delta Region Areawide Aquatic Weed Project for improved control of invasive aquatic weeds in the Sacramento-San Joaquin Delta. Journal of Aquatic Plant Management. 59s:2-15. https://apms.org/journal/.*
                                *Pratt, P.D., Moran, P.J., Pitcairn, M., Reddy, A.M., O'Brien, J. 2021. Biological control of invasive plants in California’s Delta: Past, present, and future. Journal of Aquatic Plant Management. 59s:55-66.*
                                *Portilla, M.A., Moran, P.J., Lawler, S.P. 2021. Invasive aquatic weeds influence abundances of larval mosquitoes and other invertebrates. Journal of Aquatic Plant Management. 59s:33-40.*
                                *Pitcairn, M.J., Pratt, P.D., Villegas, B., Popescu, V., Borkent, C., Reddy, A.M. 2021. Biological control of water hyacinth, Pontederia crassipes (C. Mart.) Solms (Pontederiaceae), in California: Release and re-distribution of biological control agents 1987–2006. Pan-Pacific Entomologist. 97(2):55-66. https://doi.org/10.3956/2021-97.2.55.*
                                *Ohadi, S., Laguerre, G., Madsen, J.D., Al-Khatib, K. 2022. Toward understanding the impact of nuisance algae bloom on the reduction of rice seedling emergence and establishment. Weed Science. 70(1):95–102. https://doi.org/10.1017/wsc.2021.69.*
                                *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/.*
                                *Gillard, M.B., Castillo, J.M., Mesgaran, M.B., Futrell, C.J., Grewell, B.J. 2022. Germination niche breadth of invasive Iris pseudacorus (L.) suggests continued recruitment from seeds with global warming. American Journal of Botany. 109(7):1108-1119. https://doi.org/10.1002/ajb2.16026.*
                                *Madsen, J.D., Morgan, C.M. 2021. Water temperature controls the growth of waterhyacinth and South American sponge plant. Journal of Aquatic Plant Management. 59s:28-32.*
                                *Miskella, J.J., Madsen, J.D. 2021. Mapping waterhyacinth drift and dispersal in the Sacramento-San Joaquin Delta using GPS trackers. Journal of Aquatic Plant Management. 59s:41-45. https://apms.org/journal/.*
                                *Bubenheim, D., Genovese, V., Madsen, J.D., Hard, E. 2021. Remote sensing and mapping of floating aquatic vegetation in the Sacramento-San Joaquin River Delta. Journal of Aquatic Plant Management. 59s:46-54.*
                                *Kyser, G.B., Madsen, J.D., Miskella, J., O'Brien, J. 2021. New herbicides and tank mixes for control of waterhyacinth in the Sacramento-San Joaquin Delta. Journal of Aquatic Plant Management. 59s:78-81. https://apms.org/journal/.*
                                *Miskella, J.J., Madsen, J.D., Llaban, A., Hard, E. 2021. Dissolved oxygen under water hyacinth following herbicide application. Journal of Aquatic Plant Management. 59s:82-89.*
                                *Madsen, J.D., Morgan, C., Miskella, J., Kyser, G., Gilbert, P., O'Brien, J., Getsinger, K.D. 2021. Brazilian egeria herbicide mesocosm and field trials for managing the Sacramento-San Joaquin River Delta. Journal of Aquatic Plant Management. 59s:90–97.*
                                *Jetter, K.M., Madsen, J.D., Bubenheim, D.I., Dong, J. 2021. Bioeconomic modeling of floating aquatic weeds in the Sacramento–San Joaquin River Delta. Journal of Aquatic Plant Management. 59s:98-106. https://apms.org/journal/.*


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