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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

2021 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
This is the final report for project 2030-22000-030-00D, which expired in November 2020 and has been replaced by project 2030-2230-032-00D. For additional information, see the new project’s report. For Objective 1, ARS researchers at Davis, California, led an international team to determine the influence of increases in salinity and inundation from sea level rise on the growth of native and exotic Spartina cordgrasses and their hybrid offspring in San Francisco Estuary. Published results were featured in “Special Issue on Coastal Flooding and Storm Risks” by Annals of Botany. Increased salinity and inundation led to combined effects in leaf biochemical stress responses, with variation in responses by taxa. The team completed complementary research yielding four additional publications on biochemical mechanisms underlying cordgrass stress responses. Results suggest that adaption of functional traits can support the superior invasive ability of the hybrid cordgrass taxa in California, and evaluated environmental stress effects on germination and seedling growth that are critical to establishment, spread and management of cordgrasses. In Sub-objective 1A, ARS researchers examined the phenology of curlyleaf pondweed across a range of habitats with differing hydrologies and water temperature regimes. The initiation and sprouting of curlyleaf pondweed turions, which is the critical life stage of this weed, varied based on this temperature regime. It was also not like the phenology observed for this species in the Midwestern and Northeastern U.S. states, where understanding the timing of turion formation has been critical in establishing a successful long-term management program. Under Sub-objective 1B, a series of experiments were completed examining the growth of South American spongeplant and water hyacinth in greenhouse tanks with controlled water temperatures from 15 to 30 °C (59 to 86 °F). These studies were used to generate temperature-based growth models for these two species. The shortest doubling time for water hyacinth was 7 days, while spongeplant doubling time at 25 °C was 5.7 days. These models were used by partners at the University of California, Davis, in developing bioeconomic models for the management of water hyacinth, and will inform resource managers on potential timing of management as well as time intervals for herbicide retreatment. This study also led to considering timing the start and finish of the management season by water temperature rather than the calendar, and predicting the initiation and cessation of the growing year. This study was published in a special issue of the Journal of Aquatic Plant Management. ARS scientists, working with U.S. Army Engineer Research and Development Center scientists, evaluated the phenology of three populations of flowering rush in a common garden experiment in Davis, California. This research confirmed that the growth and phenological patterns of these populations (from Idaho, Montana, and Minnesota) were identical. Similarly, the primary drivers of the plant’s phenology are water temperature and daylength. Field data confirms this pattern to be similar to that observed at the site where plants were originally collected. In this study, the peak bud density reached 250 buds per square meter, which is the equivalent of 1,250,000 buds per acre. Such significant propagule production explains why flowering rush has been successful in spreading in North American waterways. For Sub-objective 2A, ARS scientists completed phenological studies of the submersed aquatic weeds Brazilian egeria and curlyleaf pondweed, and the floating aquatic weed, water hyacinth, in the Sacramento-San Joaquin River Delta. Water hyacinth reaches peak biomass in the fall, with the highest concentration of starch at 30% dry weight. The lowest point for stored starch is in June of each year, which suggests a suitable time for control. Egeria biomass did not vary distinctly across seasons, but the stored starch had a distinct low point in late spring (April or May). Curlyleaf pondweed phenology in California differed significantly from that observed in other parts of its U.S. range, with synchronous sprouting of turions occurring in mid-winter. For each of these species, their phenological timing has important consequences for management of these species. The results of this study have been accepted for publication in a special issue of the Journal of Aquatic Plant Management. Under Sub-objective 2B, in five lab tests, exposure of the water hyacinth planthopper, Megamelus scutellaris, for 24 hours to leaf residues of 2,4-D or imazamox herbicide or a methylated seed oil adjuvant (used to help herbicides penetrate leaves) caused low (10%) insect mortality, while glyphosate and penoxsulam herbicides or a petroleum-based adjuvant caused none. In two field tank experiments, planthopper abundance was similar in herbicide-sprayed and water-sprayed tanks after 72 hours, but was reduced by 35-45% in tanks in which either of two adjuvants were sprayed, suggesting toxicity. The planthopper relies on its hard, waxy ‘skin’, which was likely damaged by the detergent-like adjuvants. For Sub-objective 2B, ARS scientists working in Davis, California, evaluated herbicides for use in the management of water hyacinth and Brazilian egeria. For egeria management, eleven herbicides were tested in mesocosm tanks. Of these, only copper chelates, fluridone, diquat, and two formulations of endothall provided better than 60% control. Environmental restrictions further limited herbicide selection for the Sacramento-San Joaquin River Delta. In field trials, fluridone provided 85% biomass reduction in three test plots, but fluridone is not suitable in all locations in the Delta. Diquat provided 80 to 90% biomass reduction in two plots. While the potassium salt of endothall only provided 43% reduction in egeria biomass, it was effective in controlling Eurasian watermilfoil and curlyleaf pondweed, two other invasive weeds in the Delta. For water hyacinth, scientists tested four herbicides not previously used in the Delta, as alternatives to glyphosate. Of these, the herbicides imazamox and florpyrauxifen-benzyl were as effective as glyphosate in controlling water hyacinth, and require less active ingredient per treated acre. These studies allowed the operational adoption of diquat for Brazilian egeria, and the adoption of imazamox and penoxsulam for control of water hyacinth and other floating weeds. Additionally, the use of imazamox and penoxsulam allow a reduction of more than 90% in herbicide used per acre while not sacrificing control efficacy. Both of the studies above have been accepted for publication in a special issue of the Journal of Aquatic Plant Management. In support of Sub-objective 2C, cytological evaluations were completed and substantial progress was made on morphometric and genetic analyses of Ludwigia populations from Florida and California to clarify their taxonomy and distribution and support evaluation of biological control agents. However, the identification of invasive water primrose species is confused and problematic, so detailed research on taxonomy is needed to identify separate species and location of origin. Exotic water primrose plants can be problematic weeds for vegetation managers of aquatic systems in California and Oregon. The weeds are native to South America and were introduced into the United States but have few natural enemies here, which may explain their abundance. ARS scientists have been working closely with Argentinian colleagues to find insects that might be safe to release in the United States to aid in the suppression of these invasive weeds. The first candidate insect slated for study is a thrips that attacks the plant’s growing foliage. Scientists have presented 15 different plant species to the thrips and monitored the insect’s ability to develop. The thrips were able to complete development on the invasive water primrose but also developed well on native and closely related species. These data indicate that the host range of the thrips is too broad for consideration as a management tool in the United States. A journal publication documenting these results was published during the fiscal year. Additional insects, particularly weevils, 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 Brazilian water weed (Egeria densa). Because previous research indicated that the fly may feed on plants in the genus Elodea, research focused on testing the fly’s ability to feed and survive on the North American native Elodea canadensis. 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 that 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 United States 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.


Review Publications
Williams, D.A., Harms, N.E., Knight, I.A., Grewell, B.J., Futrell, C.J., Pratt, P.D. 2020. High genetic diversity in the clonal aquatic weed, Alternanthera philoxeroides in the United States. Invasive Plant Science and Management. 13(4):217-225.
Reddy, A.M., Pratt, P.D., Grewell, B.J., Harms, N.E., Cabrera Walsh, G., Hernandez, C.M., Falthauser, A. 2020. Host specificity of Liothrips ludwigi, a candidate biological control agent of invasive Ludwigia spp. in the USA. Biocontrol Science and Technology. 30(11):1268-1274.
Leon-Osper, M., Infante-Izquierdo, M.D., Soriano, J.J., Nieva, F.J., Grewell, B.J., Castillo, J.M., Munoz-Rodriguez, A.F. 2020. Heat stress effects on sexual reproductive processes of a threatened halophyte. South African Journal of Botany. 133:184-192.
Madsen, J.D., Kyser, G. 2020. Herbicides for management of Waterhyacinth in the Sacramento/San Joaquin River Delta, California. Journal of Aquatic Plant Management. 58:98-104.
Turnage, G., Madsen, J.D., Wersal, R.M., Byrd, J.D., Alcott, B., Guetter, T. 2020. Selective control of flowering rush in mesocosms and field sites. Journal of Aquatic Plant Management. 58:92-97.
Goolsby, J., Hathcock, C., Vacek, A., Kariyat, R., Moran, P.J., Martinez-Jiminez, M. 2020. No evidence of non-target use of native or economic grasses and broadleaf plants by Arundo donax biological control agents. Biocontrol Science and Technology. 30(8):795-805.