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United States Department of Agriculture

Agricultural Research Service

Research Project: Aquatic and Riparian Weed Management to Protect U.S. Water Resources in the Far West United States

Location: Exotic and Invasive Weeds Research

2013 Annual Report

1a. Objectives (from AD-416):
Objective 1: Improve understanding of weed life history and population dynamics (including effects of habitat alteration and assessment in canals and managed wetlands), biosystematics, and molecular biology to develop tools to undermine the success of weeds such as water primrose-willow species, perennial pepperweed, purple loosestrife, cordgrass, giant reed, and Eurasian milfoil, and to restore invaded riparian, marsh, and aquatic ecosystems. Objective 2: Determine the effectiveness of integrated weed management, including potential new herbicides on weeds such as hydrilla (Hydrilla verticillata), pondweeds (Potamogeton, nodosus, P. crispus, Stuckenia pectinata), Eurasian watermilfoil (Myriophyllum spicatum) and exposed sediments during seasonal drawdown (dewatering) for weeds such as M. spicatum, Western milfoil (M. hippuroides) in irrigation systems. Objective 3: Determine the applicability of biological control agents for water primrose-willows, Mexican mosquito fern, Brazilian waterweed, giant reed (including tricin host production effects on natural enemies), M. spicatum, and water hyacinth (Eichhornia crassipes), including plant ecology in relation to biological control for L. hexapetala and E. crassipes. Objective 4: Develop effective rapid response methods for new introductions of aquatic invasive weeds such as E. densa, P. crispus, and Undaria, or Japanese kelp (Undaria pinnatifida), and adapt these technologies to control invasive freshwater plant species, marine macroalgae and invasive marine plants.

1b. Approach (from AD-416):
1) A demographic study will determine how temporal and spatial variation in factors affecting Uruguayan water primrose contribute to overall population dynamics and improved management and restoration at Lagun de Santa Rosa. 2) Egeria Carbon Hydrogen Nitrogen (CHN) and associated insect communities will be determined monthly at invaded/ non-invaded sites at in the Sacramento/San Joaquin Delta using presence/absence and hydroacoustical and videographic methods. 3) Eurasian watermilfoil will be sampled (weekly to monthly) in the Truckee and Fall Rivers along streamflow gradients. 4) Effects of simulated herbivory on Giant reed and effects on root growth (abundance, life span) will be quantified from images recorded with a video camera system within the minirhizotrons at weekly intervals. Success of active (planting desirable species) versus passive (recruitment from resident propagules) re-vegetation will be assessed in giant reed managed sites. 5) Effects of native and non-native submersed plants on rhizosphere microflora will be assessed in replicated mesocosms and natural populations. 6) Replicated applications of fluridone, copper will be made in water and with penoxsulam, or acetic acid to canals and canal sediment. 7) Methods to eradicate Curlyleaf pondweed will be evaluated in indoor and outdoor tanks using diquat, endothall, and penoxsulam under short and long-day conditions.

3. Progress Report:
In support of Objective 1, we tested clonal integration of resources under light regimes for Ludwigia hexapetala that may promote colonization and spread. Light strongly impacted the growth, morphology and biomass allocation in ramets regardless of integration status. Phenology shifted in shade: Ramets flowered early suggesting shade prompts a shift to sexual reproduction and dispersal via seeds. Parent ramets produced less biomass with integration, while daughters were more fit with higher biomass when integrated with a parent in sun. We tested the use of floating aquatic weeds in constructed wetlands for wastewater treatment, and added invasive L. hexapetala to anaerobic digesters for biogas production. Harvesting, sedimentation and gasification were responsible for nitrate removal, respectively. Repeat harvesting decreased nitrate removal compared to no harvesting. Biogas production offset management costs. Integrating constructed wetlands into treatment systems can enhance wastewater/organic waste treatment. We tested an integrated strategy using sheep to reduce biomass of L. hexapetala and 2 levels of tillage in a seasonal wetland, and are collecting response data. In support of Objective 2, we measured photosynthetic rates of Arundo in cultures and field sites for 3 years. We found strong linear relationships between net carbon fixation and electron transport rates. Molar ratio increased with increasing irradiance, but was negatively related to leaf temperature and intercellular CO2 concentration. Results help validate the use of fluorometry to assess photosynthetic attributes of A. donax. To evaluate A. donax contribution to flood risk, we determined Manning’s coefficient and later used it to estimate the impact of A. donax at 3 California river sites. Model simulations show that A. donax within a stream channel has a direct effect on flooded areas, causing increases up to 10% above baseline conditions. Values for Manning’s coefficient for A. donax can be used in conjunction with environmental conditions to prioritize areas for management. For objective 3, biological control studies were conducted on Hydrillia spp. flies that attack Egeria densa were located and tested in cooperation with Fundación para el Estudio de Especies Invasivas (FuEDEI) in Argentina. These agents were imported to our quarantine facility for study of their safety and impact. With FuEDEI we are also studying control agents for Ludwigia spp. Our focus is on determining which natural enemies warrant further investigation for biological control prior to requesting USDA-APHIS permits for entry into our quarantine facility. The Arundo wasp was released at one site for control of giant reed. Releases and establishment of Megamelus scutellaris for control of water hyacinth were made at 3 Delta sites, but populations are too low to measure impact. Following assessment of the lack of effectiveness of the milfoil weevil, this project has been terminated due to inadequate efficacy of the insect in coldwater rivers.

4. Accomplishments

Review Publications
Whitcraft, C., Grewell, B.J., Baye, P.R. 2012. Tidal wetland vegetation and ecotone profiles: The Rush Ranch Open Space Preserve. In: Palaima, A., editor. Ecology, Conservation, and Restoration of Tidal Marshes. Berkeley, California: University of California Press. p. 113-114.

Cohen, M.J., Hare, C., Kozlowski, J., Mccormick, R.S., Chen, L., Parish, M., Schneider, L., Knight, Z., Nelson, T.A., Grewell, B.J. 2012. Wastewater polishing by a channelized macrophyte-dominated wetland and anaerobic digestion of the harvested phytomass. Journal of Environmental Science and Health. 48(3):319-330.

Curado, G., Rubio-Casai, A., Figueroa, E., Grewell, B.J., Castillo, J.M. 2013. Native plant restoration combats environmental change: development of carbon and nitrogen sequestration capacity using small cordgrass in European salt marshes. Environmental Monitoring and Assessment. 185:8439-8449. DOI 10.1007/s10661-013-3185-4.

Spencer, D.F., Colby, L., Norris, G.G. 2103. An evaluation of flooding risks associated with giant reed (Arundo donax). Journal of Freshwater Ecology. 28:397-409. DOI:

Last Modified: 05/23/2017
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