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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

2019 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, the second year of a two-year field study of the phenology of curlyleaf pondweed (Potamogeton crispus L.) continued 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. An outdoor tank experiment was completed which evaluated increases in aqueous salinity and inundation from sea level rise on the growth of native and exotic Spartina cordgrasses and their hybrid offspring from San Francisco Estuary. Increased salinity and inundation combined to strongly influence leaf biochemical stress responses in all plant types tested. Native S. foliosa was stress-tolerant and the least sensitive to salinity, but with higher water levels, growth was severely limited. Invasive S. densiflora was fast-growing in low stress conditions and tolerated moderate interactive stresses. The exotic hybrid produced more biomass than its parents, and greater reproduction even under the most stressful conditions. Results suggest both native S. foliosa and exotic S. densiflora will experience reduced fitness, while their hybrid is more tolerant of stresses imposed by sea level rise. As a result, hybrid invasiveness may be sustained and management should be directed towards prevention of new hybrid formation. Further work for Objective 1 was completed, 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 have been analyzed for nitrogen content. Initial analysis of growth found no difference in the seasonal growth of B. umbellatus populations from Idaho, Montana, and Minnesota. For Objective 1, greenhouse studies were completed in which the submersed invasive plant Brazilian waterweed (Egeria densa), was grown at water temperatures from 10 to 30 centigrade (C). Egeria requires water temperatures of greater than 16 C for growth, despite the presence of green shoots at all temperatures. Studies of the effect of water temperatures on the growth of significant invasive aquatic plants will continue with curlyleaf pondweed and Eurasian watermilfoil. This information will assist managers in timing the active growth periods of target invasive plants in water resources across the country. For Objective 2, all analyses of starch in the storage structures of waterhyacinth, Brazilian waterweed and curlyleaf pondweed from the 32-month study of phenology of these species in the Sacramento-San Joaquin River Delta were completed. Data analysis and preparation of a final manuscript on this effort are currently underway. Seasonal patterns with distinct repeating low points were identified for all three species, which may be useful in targeting the timing of management. Under Sub-Objective 2B, studies of the toxicity of four herbicides and two adjuvants to the water hyacinth planthopper were completed by applying herbicide/adjuvant or water on field tanks containing caged colonies of the planthopper on water hyacinth. The results were similar to prior lab tests indicating that the herbicides and adjuvants are not directly toxic to the planthopper. To further support Objective 2, herbicide trials were completed in outdoor tanks at the USDA ARS facility in Davis, California. Brazilian waterweed was exposed to label-approved concentrations of bispyrabic-sodium, carfentrazone-ethyl, complexed copper, diquat, the dipotassium salt of endothall, the dimethylamine salt of endothall, florpyrauxifen-benzyl, flumioxazin, fluridone, imazamox, and penoxsulam for a 10-week static exposure. Complexed copper, diquat, the dimethylamine salt of endothall, and fluridone provided more than 80 percent control of Brazilian waterweed. Carfentrazone-ethyl and the dipotassium salt of endothall provided more than 60% control. All other herbicides provided less than 50 percent control, though all herbicides tested resulted in significant growth suppression as compared to an untreated reference. Field assessments of efficacy indicated that fluridone, diquat, and the dipotassium salt of endothall all provide significant control of Brazilian waterweed. Under Objective 2, progress continued on comparative analyses of morphometric, cytological and genetic data of Ludwigia populations from Florida and California to support evaluation of biological control agents. However, scheduled collaborative work on this effort was delayed by the government shutdown. ARS scientists have identified the need for further sequencing of haplotypes, and additional DNA analyses using ITS markers are underway to assess potential recent hybridization among invasive taxa. Exotic plants in the genus Ludwigia can be problematic weeds 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 to aid in the suppression of invasive Ludwigia species. The first candidate insect slated for study is a thrips native to Argentina. Scientists have presented 15 plant species individually to the thrips and monitored the insect’s ability to develop. The thrips was able to complete development on the invasive Ludwigia species but also developed well on native Ludwigia species. These data indicate that the host range of the thrips is too broad for consideration as a management tool in the U.S. A publication documenting these results is being prepared for submission to a peer-reviewed journal. Additional insects, particularly weevils in the genus Tyloderma, were acquired from colleagues in Uruguay and are currently under study. The Argentinean fly, Hydrellia egeriae, is considered the best candidate biological control agent of the invasive weed Egeria densa. Because previous researchers indicated that the fly may feed on non-target Elodea species, 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. A series of tests showed that the number of eggs laid were similar on Egeria and Elodea; both plants were suitable for fly development but Egeria was a superior host, and there was no difference in egg production between the flies on the two plants. These data indicate that H. egeriae might be able to attack Elodea in the U.S. 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 report documenting these data have been published in a peer-reviewed journal.

1. New application for legacy herbicide in combating invasive Bazilian waterweed. For the past decade, the only herbicide used to manage the invasive aquatic weed, Brazilian waterweed, in the Sacramento-San Joaquin River Delta was fluridone. This required up to 16 weekly applications of granular herbicide for effective control, and could not be used near irrigation water intakes or in areas of high water movement. Recent testing at the USDA ARS facility in Davis, California, found that diquat provided over 90 percent control of Brazilian waterweed. Diquat requires only a short exposure time to be effective, and residues quickly dissipate from natural waters. A field assessment found diquat to be highly effective, and require retreatment at no more than every four weeks to remain effective. Herbicide costs would be 60 percent less with a diquat regimen than with fluridone. Since diquat acreage is limited under current permits, it would be used only at sites in which fluridone has not achieved control.

Review Publications
Gallego-Tevar, B., Rubio-Casal, A., De Cires, A., Figueroa, E., Grewell, B.J., Castillo, J.M. 2018. Phenotypic plasticity of polyploid plant species promotes transgressive behavior in their hybrids. AoB Plants. 10(5):ply055.
Gallego-Tévar, B., Grewell, B.J., Vallet, D., Rousseau, H., Keller, J., Lima, O., Dreano, S., Salmon, A., Figueroa, E., Ainouche, M., Castillo, J. 2019. Genetic structure of Spartina hybrids between native Spartina maritima and invasive Spartina densiflora in southwest Europe. Perspectives in Plant Ecology, Evolution and Systematics. 37:26-38.
Gallego-Tevar, B., Infante-Izquierdo, M.D., Figueroa, E., Munoz-Rodriquez, A.F., Grewell, B.J., Castillo, J.M. 2019. Some like it hot: Maternal-switching with climate change modifies formation of invasive Spartina hybrids. Frontiers in Plant Science. 10:484.
Carter, C., Ervin, G., Madsen, J.D. 2018. Effects of initial propagule size and water depth on Butomus umbellatus L. growth and vegetative propagation. Aquatic Botany. 150:27-32.