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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

2012 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:
Substantial progress was made to improve knowledge and control of aquatic and riparian weeds. Arundo donax (giant reed): Experiments evaluated whether defoliation or leaf damage affect stem growth, leaf production, or photosynthetic rates. Defoliation did not affect stem height or leaves per stem, leaf damage did not affect electron transport rates (ETR), and defoliated stems maintained ETRs similar to rates of undamaged leaves suggesting low to moderate leaf damage or defoliation alone may not significantly reduce growth or the persistence of A. donax. Cyanobacteria: In water-seeded rice systems, Nostoc spongiaeforme hinders crop growth by dislodging and reducing light to seedlings. We investigated the timing of P fertilizer application to reduce cyanobacteria while maintaining rice yields and water quality. Early-season water P concentration and Nostoc occurrence were highest when fertilizer was applied pre-plant. In fields with delayed P application, water P increased immediately following application but subsequently declined. Further trials confirm that delayed fertilizer applications can maximize rice yield while reducing early-season interference from cyanobacteria. Ludwigia (water primroses): Field experiments tested integrated management methods for L. hexapetala control. Hydrologic control with mechanical removal and glyphosate use improved efficacy in canals. Timing and frequency of disking were evaluated for control in seasonal wetlands. Disking at flowering stage improved control and reduced emergence of L. hexapetala from soil seed banks. Sheep grazing trials to reduce biomass prior to disking and reduce management cost are underway. In mesocosms, we are evaluating functional traits and physiological integration by L. hexapetala for control across resource gradients. Lepidium latifolium (pepperweed): Field experiments suggest 2,4-D has minimal non-target effects but does not provide effective control in estuarine wetlands, while Imazapyr reduced cover by 90% but had persistent non-target effects to native vegetation. Biological Control: Field assessments of herbivores feeding on Egeria densa did not reveal effective natural enemies in the Sacramento/ San Joaquin Delta, reinforcing the need to test newly identified fly species (Hydrillia spp.) in South America that are now permitted for entry. Colonies of Euhrychiopsis lecontei are being maintained for assessment of their efficacy for control of Eurasian watermilfoil in cold water habitats. Field and modeling studies indicate weevils from midwestern US will not be effective in California. Locally-collected colonies are being assessed. Natural enemies of Ludwigia spp. are under study, including resident flea beetle Altica litigata, for defoliation potential. Studies to identify and use insect pheromones as aggregation agents have been assessed. Molecular studies separating A. litigata from closely related species indicate California specimens are unique relative to similar insects elsewhere in USA. A South American insect, Megamelus scutellaris, has been released in the Delta where survival and efficacy assessments for waterhyacinth control are underway.

4. Accomplishments
1. Improving biological control of Eurasian watermilfoil. A combined field assessment and modeling study documented that the native North American insect Euhrychiopsis lecontei was not predicted to be an effective natural enemy of Eurasian watermilfoil in the Fall River of California. This spring-fed river has very cold water that allows Eurasian watermilfoil to grow, yet is too cold for this insect to substantially impact this plant under these conditions. Water temperatures typically remain below the ovipositional threshold of 15 degree C in this waterway. ARS scientists from Davis, and Albany, CA, assessed environmental conditions at 71 monitoring stations along this 35 km long waterway to determine that Eurasian watermilfoil growth and development can occur along the entire waterway, however, the biological control insect would only be able to live and reproduce in a limited fashion and thus not significantly suppress this aquatic invasive weed. This work is important as local land and waterway managers saved spending $100,000s on weevil augmentation programs that would be expected to fail. Now, ARS scientists are working to assess other means of controlling this pest plant.

2. Rapid response to winged primrose-willow. In late summer 2011, a newly introduced species of Ludwigia invaded rice fields in Butte County, California. ARS scientists from Davis, California, used morphological and cytological methods to confirm the identification of winged primrose-willow (Ludwigia decurrens) from South America, and then worked with local land managers to eliminate this new weed and to block future introduction pathways. California rice production on 500,000 acres in the Sacramento Valley contributes over $1.3 billion dollars annually to the California economy. In recent years, weed control costs have skyrocketed reducing profitability of production, and rice producers have seen dramatic increases in the resistance of weeds to conventional herbicides. The most effective, economical, and ecologically sound approach to managing invasive plants is to prevent their invasion in the first place, and proactive response to new weeds with rapid detection, response and eradication is imperative. ARS delivered educational presentations on identification and rapid response management techniques at four winter rice grower workshops throughout the Sacramento Valley, and assisted University of California Cooperative Extension farm advisors and agricultural commissioners with outreach education for prevention of the spread of winged primrose-willow in rice fields and adjacent, natural wetlands.

Review Publications
Grewell, B.J., Whitcraft, C., Baye, P. 2011. Estuarine Vegetation at Rush Ranch Open Space Preserve, San Francisco Bay National Estuarine Research Reserve, California. San Francisco Estuary and Watershed Science. 9(3):1-29 and Appendix, 21pp.

Whitcraft, C.R., Grewell, B.J. 2011. Evaulation of perennial pepperweed (Lepidium latifolium) management in a seasonal wetland in San Francisco Estuary prior to restoration of tidal hydrology. Wetlands Ecology and Management. 20:35-45.

Spencer, D.F., Liow, P., Lembe, C.A. 2013. Influence of a non-copper algicide on the cyanobacterium, Nostoc spongiaeforme, and the green alga, Hydrodictyon reticulatum, in field and laboratory experiments. Paddy and Water Environment. 11(1):611-617.

Spencer, D.F. 2012. Response of Arundo Donax to Intermittent Shading. Journal of Invasive Plant Science and Management. 5:317-322.

Lundy, M.E., Spencer, D.F., Van Kessel, C., Hill, J.E., Linquist, B.A. 2012. Managing phosphorus fertilizer to reduce algae, maintain water quality, and sustain yields in water-seeded rice. Field Crops Research. 131(2012):81-87 doi:10.1016/j.fcr.2012.03.005.

Drenovsky, R.E., Grewell, B.J., D'Antonio, C.M., Funk, J.L., James, J.J., Molinari, N., Parker, I.M., Richards, C.L. 2012. A functional trait perspective on plant invasion. Annals Of Botany. 110:141-153.

Last Modified: 06/25/2017
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