Skip to main content
ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #429011

Research Project: Enhancing Water Resources Stewardship through Aquatic and Riparian Weed Management

Location: Invasive Species and Pollinator Health

2018 Annual Report

The long-term objective of this project is to develop and enhance integrated plant management approaches for invasive aquatic plants significant to U.S. Pacific West watersheds. This will be accomplished by developing a better understanding of weed biology and ecology, and the application of multiple management techniques on target invasive plants. Specifically, during the next five years we will focus on the following objectives: Objective 1: Determine the effects of specific environmental parameters (i.e., carbon dioxide concentration, temperature, light, hydroperiod, sediment nutrient levels, and salinity) on aquatic plant growth for key invasive weeds of the Pacific West watersheds. Subobjective 1A. Determine the relative importance of environmental drivers (e.g. light, temperature) controlling the growth or response to climate change of submersed invasive aquatic plant species. Subobjective 1B. Determining the environmental drivers influencing the growth of emergent and floating aquatic plant species. Objective 2: Develop environmentally safe, yet effective, integrated weed management approaches for aquatic and riparian weeds by identifying critical points in plant life histories to target, and by integrating biological, chemical, mechanical and cultural control strategies. Subobjective 2A. Phenology and life history considerations in long-term management of the invasive plants curlyleaf pondweed, egeria, and flowering rush. Subobjective 2B. Development and evaluation of integrated pest management techniques for invasive aquatic plants. Subobjective 2C. Evaluate the potential for biological control of invasive aquatic plant populations.

1. Sediment fertility will be more significant for the growth of all submersed species; Eurasian watermilfoil (M. spicatum), curlyleaf pondweed (P. crispus), monoecious hydrilla (Hydrilla verticillata), egeria (Egeria densa), cabomba (C. caroliniana), and elodea ( Elodea canadensis) than water column fertility. The growth potential of rooted submersed macrophytes will be examined in outdoor tank experiments with a range of sediment and water column nutrients. 2. Dense mats of Eichhornia crassipes cause higher rates of phosphorus release from sediments than found in either native vegetation or unvegetated, open water areas, causing internal loading of phosphorus throughout the summer. This hypothesis will be tested by measuring levels of inorganic P, pH, DO, and temperature in the water column under water hyacinth mats and in adjacent stations with native floating or emergent plants, and open water stations free of water hyacinth at multiple sites in the Delta. 3. Interspecific differences in responses of invasive and native cordgrasses to inundation and salinity with rising sea level in Pacific Coast estuaries. In a full factorial experiment, we will cross 3 Spartina species (native S. foliosa, and alien S. densiflora, S. alterniflora) with 3 aqueous salinity levels (0,15,30 ppt) and 3 simulated tidal inundation treatments (25, 50 or 100% of a tidal cycle) for 27 treatment combinations replicated 6 times (n=162) in a randomized complete block design with all treatment types at each site (block). 4. Characterize the phenology of curlyleaf pondweed (Potamogeton crispus L.) and egeria (Egeria densa Planch.) in the Delta to identify long-term management endpoints and timing of management, and test the operational management program for meeting the goal of long-term plant reduction. In the first phase, the phenology of these two species will be studied over a two-year time period. In the second phase, potential improvements in management will be documented in operational treatments. 5. The planthopper Megamelus scutellaris will not show mortality after direct exposure to residues of 2,4-D, glyphosate, penoxsulam or imazamox, but will show mortality after exposure to nonionic crop oil based adjuvants. In mesocosms, populations of the planthopper on plants to which herbicides are applied will suffer little or no mortality and will establish populations on simulated recolonization plants. 6. Develop use patterns of recently labeled aquatic herbicides for control of water hyacinth and egeria in the Delta. We propose two series of experiments to evaluate new active ingredients that have been approved for aquatic use in California: imazamox, imazapyr, penoxsulam, byspyribac sodium, flumioxazin, topramezone, and carfentrazone. In the first series, water hyacinth control will be examined with foliar treatments of imazamox, imazapyr, penoxsulam, bispyribac sodium, flumioxazin, topramezone, triclopyr and carfentrazone. Treatments with 2,4-D and glyphosate will be added as the two current standard treatments. 7. Determine correct taxonomy of invasive Ludwigia in Florida, and compare with populations in California, Oregon and South America.

Progress Report
In support of Objective 1, a two-year study of the phenology of curlyleaf pondweed (Potamogeton crispus L.) was initiated in a cool-water lake (Lake Berryessa), a cold-water stream (Putah Creek), and a tidal freshwater estuary (Sacramento/San Joaquin River Delta). All three sites are in the same watershed, but experience different water movement and temperature conditions. Preliminary observations are that phenological characteristics are different between these three sites, but similar within three sampling plots in each of the sites. This research complements and continues phenological studies recently concluded in the Sacramento/San Joaquin River Delta that examined three species, including P. crispus, over a two-year period. The present study is designed to identify how varying water temperature regimes impact the phenology of P. crispus, which is critical in implementing long-term control of this species. To support Objective 1, research continued to evaluate the results of a mesocosm experiment to evaluate influence of increasing aqueous salinity and inundation from sea level rise on the growth of cordgrasses, including invasive Spartina densiflora, native S. foliosa and their hybrid offspring from San Francisco Estuary. To evaluate responses to anoxia stress and salinity, post-harvest analyses of leaf tissue samples from 144 plants were analyzed for carbon (C), nitrogen (N), sodium, photosynthetic pigments, glycinebetaine, and proline. Rhizome tissues were analyzed for C, N, and total nonstructural carbohydrates. These data along with pre-harvest measures of leaf morphological responses, and post-harvest measures of root porosity, biomass and allocation, have been organized by functional trait groups and statistical analyses. Manuscript preparation is underway. A two-year study was completed under Objective 1 in which plants from three flowering rush (Butomus umbellatus L.) populations across the western U.S. were grown together at the Aquatic Weed Research Facility in Davis, California. This type of study is widely known as a “common garden” experiment. Rhizomes have been analyzed for starch content, and all plant tissues are being prepared for nitrogen analysis. Initial analysis of growth found no difference in the seasonal growth of B. umbellatus populations from Idaho, Montana, and Minnesota. Preliminary results of flowering rush growth from this study have been presented to regional and national professional conferences. For Objective 1, greenhouse studies under controlled water temperatures at temperatures from 10 to 30 degrees Celsius (C) were completed for water hyacinth (Eichhornia crassipes) and spongeplant (Limnobium laevigatum). For each species, two experiments were completed in which plants were grown at controlled temperatures with biomass collected weekly for six weeks to calculate relative growth rates. Preliminary results suggest that plant growth does not occur below 15 C for both species, with optimal growth between 25 and 30 C. For water hyacinth, positive relative growth rates intercepts zero at 16 to 18 C. Calculated doubling time at optimal temperatures was approximately eight days. Results for water hyacinth growth were presented at a regional weed science conference. Future work will focus on the response of significant submersed weeds to temperature regime, to allow prediction of when these species will start growing during the season in managed waterbodies. For Objective 2, sampling for a 32-month study of the phenology of waterhyacinth (Eichhornia crassipes), Brazilian waterweed (Egeria densa), and curlyleaf pondweed (Potamogeton crispus) was completed in the Sacramento/San Joaquin River Delta. For each species, three sites were sampled monthly for biomass. Plant samples are currently being ground for analysis of tissue carbohydrates and nitrogen. Preliminary results have been presented to a regional scientific society. Under Objective 2, laboratory tests of the toxicity of four herbicides and two adjuvants on dipped leaves to the water hyacinth planthopper, Megamelus scutellaris, were completed. In a total of five tests, 24 hours of exposure to residue of 2,4-D or imazamox, or to a methylated seed oil adjuvant, caused slight toxicity (less than 10% after correcting for water-dipped control). Glyphosate and penoxsulam herbicides and a petroleum-based adjuvant caused no mortality. Overall, lab exposure to herbicide or adjuvant residues did not adversely affect planthopper survival. Assessments of exposure of planthoppers to these herbicides and adjuvants in outdoor caged colonies were initiated. To further support Objective 2, herbicide trials have been completed in the area of the Sacramento/San Joaquin River Delta examining herbicide tank mixes for control of waterhyacinth. The study examined carfentrazone, flumioxazin, imazamox, and glyphosate, as well as tank mixes of carfentrazone + imazamox, carfentrazone + glyphosate, flumioxazin + imazamox, and flumioxazin + glyphosate. Preliminary results indicate that tank mixes resulted in only additive effects with the systemic herbicide. In many instances, the tank mix was no better than the primary systemic herbicide alone. Imazamox and glyphosate both provide good control of waterhyacinth. In addition, a mesocosm tank study examining the available aquatic herbicides for control of Brazilian waterweed (Egeria densa) has been initiated. Results for the Egeria study are pending. Under Objective 2, cytogenetic evaluations differentiated invasive Ludwigia populations in California, Florida, Argentina and Uruguay to support evaluation of potential biological control agents. Sequenced chloroplast DNA distinguished haploid types from inherited genes and lineage relationships among samples. Results indicate all sampled octoploid and decaploid genotypes from Florida and California are a single haplotype that is also the same as several South American populations. Amplified fragment length polymorphisms (AFLP) genotyping revealed a single genotype common to several L. hexapetala populations in Florida and California, supporting upcoming host specificity testing with potential biological control insects. Cytological results suggest the need for further DNA analyses. Internal transcribed spacer (ITS) markers will be evaluated to further elucidate phylogenetic relationships and assess potential recent hybridization among taxa. Morphometric analyses are being compared with cytogenetic results to support species identification. Exotic Ludwigia species are among the weeds of greatest concern for vegetation managers of aquatic systems in California and Oregon. ARS scientists have been working closely with Argentinian colleagues to investigate the use of insects as biological control agents to aid in the suppression of invasive Ludwigia species. The first candidate insect slated for study is a thrips native to Argentina. Unfortunately, collaborators in Argentina were unable to secure an export permit for the insect. Progress continues on this front, but final hurdles still need to be crossed at the national level for Argentine regulators to approve insect exports. In the meantime, ARS scientists are working with scientists in Uruguay to acquire export permits for insects native to their country, but considered problematic weeds in the Western U.S. The environmental safety of Argentinean fly, Hydrellia egeriae, as a biological control agent of Egeria densa in the Western U.S. was evaluated during 2015-2016. Because previous researchers indicated that the fly may feed on non-target Elodea spp., host specificity tests focused on Elodea canadensis, a native plant that has a widespread distribution in North America. Experiments were conducted by presenting flies either the target weed or the non-target plant singly or in combination. In the no-choice test, the number of eggs laid were similar on Egeria and Elodea. In the choice tests, more eggs were laid on Egeria, although a few eggs were still laid on Elodea. A third test measured the suitability of both plants for fly development. Survival was greater on Egeria compared with Elodea. A final test showed that there was no difference in egg production between the flies on the two plants, indicating that H. egeriae might be able to attack Elodea and establish in the field if it were released. The findings indicate that the host range of the fly H. egeriae is too broad for use as a biological control agent and further resources dedicated to the development of this insect are unwarranted. A publication documenting these data has been prepared and submitted to a peer reviewed journal.

1. Evaluation of reduced-risk herbicides for control of water hyacinth. ARS scientists in Davis, California, collaborating with personnel from the California State Parks Division of Boating and Waterways, and the University of California Cooperative Extension, completed an evaluation of the reduced-risk aquatic herbicides, imazamox and penoxsulam, in comparison with the legacy herbicides, 2,4-D and glyphosate. The evaluation found that using approved label rates of imazamox and penoxsulam would provide control of water hyacinth (Eichhornia crassipes) equal to or better than using glyphosate, while reducing the risk factor to endangered species and species of concern. A primary concern for implementing aquatic weed management activities in the Sacramento/San Joaquin River Delta is potential harm to endangered fish species, such as Delta Smelt and Pacific Salmon. Water resource managers who adopt the new management program are reducing the total amount of herbicides introduced into the water by 60-90% per treated acre.

Review Publications
Wersal, R.M., Madsen, J.D. 2018. Designing and using phenological studies to define management strategies for aquatic plants. Journal of Aquatic Plant Management. 56:83-89.
Castillo, J.M., Gallego-Tevar, B., Figueroa, E., Grewell, B.J., Vallet, D., Rousseau, H., Keller, J., Lima, O., Dreano, S., Salmon, A., Ainouche, M. 2018. Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific Coast of North America. Ecology and Evolution. 8(10):4992-5007.
Turnage, G., Wersal, R.M., Madsen, J.D. 2017. Phenology of curlyleaf pondweed (Potamogeton crispus L.)in the southeastern US: a two year mesocosm study. Journal of Aquatic Plant Management. 56:35-38.
Calomeni, A.J., Geer, T., Lwinski, K., Rodgers, J.H., Madsen, J.D., Wersal, R.M. 2017. Monitoring for national pollutant discharge elimination system permit requirements: Algaecides. Journal of Integrated Pest Management. 8(1):1-9.