Location: Invasive Species and Pollinator Health
2020 Annual Report
Objectives
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.
Approach
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, ARS researchers at Davis, California, led an international team and completed experiments to evaluate 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 synergetic 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. Hybrid cordgrass taxa in California have traits that are superior for invasive ability than either parental cordgrass species. The researchers evaluated environmental stress effects on germination and seedling growth that are critical to establishment, spread and management of cordgrasses.
Under Sub-objective 1A, ARS scientists completed phenological studies of the submersed aquatic weeds Brazilian egeria and curlyleaf pondweed, and the floating aquatic weed waterhyacinth, in the Sacramento-San Joaquin River Delta. Waterhyacinth 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, 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. For instance, waterhyacinth is only actively growing from May through October, so herbicide treatments outside this window are not effective, but harvesting stembases may have substantial benefit, even in mid-winter. For curlyleaf pondweed, the prescription of a spring or early summer treatment to prevent turion formation would not have the same benefit as observed in Midwestern United States, but potential treatments in the late winter might capture turions as they are sprouting. The results of this study have been accepted for publication in a special issue of the Journal of Aquatic Plant Management.
Under Sub-objective 1B, a series of experiments were completed examining the growth of South American spongeplant and waterhyacinth 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 waterhyacinth was seven days (at both 25 and 30 °C), 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 waterhyacinth, and will inform resource managers on potential timing of management as well as time intervals for herbicide retreatment. This study will be published in a special issue of the Journal of Aquatic Plant Management.
Under Sub-objective 2B, two experiments in field tanks (mesocosms) on the water hyacinth planthopper, Megamelus scutellaris, were completed to test the hypothesis that 2,4-D, glyphosate, penoxsulam and imazamox herbicides are not toxic, but two crop oil surfactants (detergents), used to help herbicides penetrate waxy plant leaves, are mildly toxic. Planthopper abundance 72 hours after spraying infested plants in mesocosms was similar in herbicide-sprayed and water-sprayed (control) mesocosms, but was reduced 35-45% in tanks in which either of the two surfactants were sprayed, suggesting toxicity. The planthopper relies on its hard, waxy ‘skin’ (cuticle), which was likely damaged by surfactants. Planthopper populations varied between mesocosms, however, and additional needed studies were delayed by maximized telework due to COVID-19.
For Sub-objective 2B, scientists working in Davis, California, evaluated herbicides for use in the management of waterhyacinth and Brazilian egeria. For egeria management, 11 herbicides had been 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 usable 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 waterhyacinth, 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 waterhyacinth, and require less active ingredient per treated acre. Both of the studies above have been accepted for publication in a special issue of the Journal of Aquatic Plant Management.
In further support of Objective 2, cytological evaluations were completed and 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. Substantial progress was made, but maximized telework due to COVID-19 delayed laboratory analyses, including morphometric evaluations and further DNA sequencing to assess unexpected potential recent hybridization among invasive taxa.
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 was 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 Argentinian 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. Also, both plants were suitable for fly development, but Egeria was a superior host. 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 has been published in a peer-reviewed journal.
Accomplishments
1. Hybridization supports increased stress tolerance and invasiveness of cordgrass with sea level rise. Nonnative Spartina cordgrasses and their hybrid offspring are aggressive invaders of California estuaries. In a greenhouse experiment, ARS researchers at Davis, California, subjected two parental cordgrass species (native S. foliosa; alien S. densiflora) and their hybrid taxa to four levels of aqueous salinity and three inundation regimes in aquatic mesocosms. Native S. foliosa was stress-tolerant and the least sensitive to salinity, but growth was severely limited with increased inundation. S. densiflora was fast-growing in low stress conditions and tolerated moderate interactive stresses. The exotic hybrid produced more biomass than its parents, and achieved high fitness even under the most stressful conditions. Expression of extreme traits by the hybrid relative to it parents was greater in response to increasing inundation than to salinity. Results suggest both native S. foliosa and alien S. densiflora will experience reduced fitness, while their hybrid is more tolerant of stresses imposed by sea level rise. Findings support west coast efforts for Spartina eradication; management should be directed towards prevention of new hybrid formation.
Review Publications
Grewell, B.J., Futrell, C.J., Iannucci, M., Drenovsky, R.E. 2019. Resprouting potential of rhizome fragments from invasive macrophyte reveals superior colonization ability of the diploid congener. AoB Plants. 11(6). https://doi.org/10.1093/aobpla/plz071.
Gallego-Tevar, B., Grewell, B.J., Futrell, C.J., Drenovsky, R.E., Castillo, J.M. 2019. Interactive effects of salinity and inundation on native Spartina foliosa, invasive S. densiflora, and their hybrid from San Francisco Estuary, California. Annals Of Botany. 125(2):377-389. https://doi.org/10.1093/aob/mcz170.
Gallego-Tevar, B., Peinado, P., Alvarez, R., Gandullo, J., Grewell, B.J., Figueroa, E., Castillo, J.M. 2019. Changes to the functional traits of phosphoenolpyruvate carboxylase following hybridization in C-4 halophytes. Physiologia Plantarum. 169(1):83-98. https://doi.org/10.1111/ppl.13053.
Gallego-Tevar, B., Grewell, B.J., Drenovsky, R.E., Castillo, J.M. 2019. Transgressivity in key functional traits rather than phenotypic plasticity promotes stress tolerance in a hybrid cordgrass. Plants. 8(12):594. https://doi.org/10.3390/plants8120594.
Infante-Izquierdo, M.D., Castillo, J.M., Grewell, B.J., Nieva, F.J., Munoz-Rodriguez, A.F. 2019. Differential effects of increasing salinity on germination and seedling growth of native and exotic invasive cordgrasses. Plants. 8(10):372. https://doi.org/10.3390/plants8100372.
Infante-Izquierdo, M.D., Polo-Avila, A., Sanjose, I., Castillo, J.M., Nieva, F.J., Grewell, B.J., Munoz-Rodriguez, A.F. 2020. Effects of heavy metal pollution on germination and early seedling growth in native and invasive Spartina cordgrasses. Marine Pollution Bulletin. 158:111376. https://doi.org/10.1016/j.marpolbul.2020.111376.
Gallego-Tevar, B., Peinado-Torrubia, P., Alvarez, R., Grewell, B.J., Castillo, J.M. 2020. From physiology to salt marsh management challenges with sea level rise: the case of native Spartina foliosa, invasive S. densiflora and their hybrid. Conservation Physiology. 8(1). Article coaa053. https://doi.org/10.1093/conphys/coaa053.
Hofstra, D., Schoelynck, J., Ferrell, J., Coetzee, J., De Winton, M., Bickel, T., Champion, P., Madsen, J.D., Bakker, E., Hilt, S., Matheson, F., Netherland, M., Gross, E. 2020. On the move: New insights on the ecology and management of native and alien macrophytes. Aquatic Botany. 162:103190. https://doi.org/10.1016/j.aquabot.2019.103190.
