Location: Invasive Species and Pollinator Health
2017 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
For Objective 1, ARS scientists sampled curlyleaf pondweed biomass in the Sacramento/San Joaquin River Delta. The phenology of curlyleaf pondweed is highly variable across the Delta, possibly in response to under water temperature and water quality differences across the Delta. Scientists delayed sampling at other locations due to the high water flows throughout California in the first half of the calendar year.
Research continued to evaluate the influence of climate change and sea level rise on the growth and potential spread of invasive cordgrass species in San Francisco Estuary. Live plant cultures of native S. foliosa, exotic S. densiflora and their hybrid were cultivated from rhizomes, and methods were tested. A full factorial experiment to test the effects of increasing salinity and inundation regimes on survival, growth, biomass allocation, anatomical, physiological and biochemical responses of the three taxa was implemented using 144 plants in 16 aquatic mesocosms.
Phenology of flowering rush populations from three distinct locations in the western United States is being investigated in Objective 1 as part of a common garden experiment at the Davis, California facility. Populations are grown in separate vaults and sampled monthly throughout the year, with plant growth characteristics (emergence, shoot height, flowering) recorded weekly. The three populations follow very similar growth trajectories throughout the year. Although the populations are from distinct watersheds in western Montana, eastern Idaho, and northwestern Minnesota, genetic analysis has found that they are virtually identical. One significant result of this study is that rhizome buds, which some investigators refer to as bulbils, are initiated in June and are produced continuously through September, when the plants senesce.
In further support of Objective 1, the growth of water hyacinth and South American spongeplant under four controlled temperature levels were investigated in greenhouse tanks with controlled water temperatures. While air temperature may effect leaf photosynthesis, the growth of new leaves and roots are dominated by water temperature. Increasing water temperatures are one factor driving the growth of these free-floating plants and a contributing factor in heavy plant growth in drought years where low water flows result in higher water temperatures. In an additional study, scientists examined the regrowth of water hyacinth stembases to water temperatures of 5, 10, and 15 Celsius. Water hyacinth leaf emergence and growth was suppressed at 5 and 10 C, but significant at 15 C. The onset of this trigger temperature is one factor in the phenology and growth of water hyacinth.
For Objective 2, the phenology of water hyacinth, egeria, and curlyleaf pondweed have been studied at three sites for each species in the Sacramento/San Joaquin River Delta. For each species, ARS scientists collected biomass samples at three sites each month. In addition, six sites in the Delta were also used to collect air temperature on a continuous basis, and water temperature is collected on a continuous basis at all nine sites. These studies have already contributed to the management strategies for these three species. Studies indicate that water hyacinth in some years can begin growth even before the current regulatory framework allows for management, and growth rates exceed the current retreatment restrictions for water hyacinth. Egeria phenology studies have contributed to the concept that management can proceed both earlier than in the past, and continue later as necessary since this plant is an evergreen perennial. These considerations are being included in the new Aquatic Invasive Plant Control Program protocol for the Delta.
Also for Objective 2, three sites in Idaho and Montana are being sampled four times per year for flowering rush biomass and phenology. At each location, air and water temperature are measured continuously. All three sites have fluctuating hydrology, which is typical of flowering rush habitats in the far western United States. The phenology and life history of flowering rush is well adapted for sites in which water levels can fluctuate ten to twenty feet during the year. One significant result from this is these plants are producing up to five million rhizome buds (or bulbils) per acre, which is a propagule density that is often only seen in seed-producing plants. Management must focus on reducing or stopping rhizome bud formation.
In four tests, the water hyacinth planthopper Megamelus scutellaris showed no enhanced mortality after one week when exposed for 24 hours to residue on leaves dipped in any of four herbicides or two adjuvants compared to planthoppers exposed to water-dipped leaves. These results suggest that exposure to herbicide or adjuvant residues on feeding surfaces does not adversely affect biocontrol agent survival.
ARS scientists completed an initial evaluation of new herbicides for the control of water hyacinth using imazamox and penoxsulam, compared to the standard treatments of 2,4-D or glyphosate. In the first study, imazamox (controlled 93% of the weeds) and penoxsulam (94% control) provided comparable levels of control to the standard treatments of 2,4-D (82% control) and glyphosate (87% control). In a second study, four rates each of imazamox and penoxsulam were examined. In this study, imazamox treatments and penoxsulam treatments provided better control than the standard glyphosate treatment. It is possible that these new reduced risk herbicides can provide the same or better control while reducing herbicide loading rates into water bodies by 75 to 98%. Herbicide resistance management, however, will be imperative as part of using these two herbicides.
Scientists completed an initial screening of 10 aquatic herbicides on Brazilian waterweed using an eight week static exposure in mesocosm tanks. In this test, only complexed copper-ethylenediamene, diquat, and the dimethylalkylamine salt of endothall provided significant control. Further testing will be performed.
Also for Objective 2, scientists evaluated invasive Ludwigia populations in Kissimmee and Alligator Chain of Lakes, Kissimmee River, and Lake Okeechobee watersheds of Florida. Plants were collected, imported and cultivated in Davis, California. All cytological and genetic analyses of 199 individual plants were completed, and chromosome counts were obtained from evaluation of 1,591 cell images from these individuals. The spatial distribution of diploid, hexaploid, octoploid, and decaploid cytotypes was determined. Genetic results were obtained from the same individuals for comparison with specimens from invasive populations in California, and native populations in the native South American range. Morphometric analysis of field and cultured specimens are underway. Significant progress was made towards clarifying taxonomic and genotypic identity of invasive Ludwigia taxa to support evaluation of potential biological control agents and development of integrated management strategies.
Exotic Ludwigia species continue to be weeds of concern for vegetation managers in the Delta and beyond. ARS scientists have been working closely with Argentinian colleagues to investigate the use of insects to aid in the suppression of invasive Ludwigia species. Insects that feed on and damage only Ludwigia, but don’t attack non-target plants, may be very useful tools for holistically controlling Ludwigia in the United States. The first candidate insect slated for study is a very small thrips native to Argentina. Unfortunately, collaborators in Argentina were unable to secure an export permit for the insect so it can be tested for environmental safety. Progress on this front is limited until Argentine regulators approve the export to the U.S. of the insect for use in research. In the meantime, ARS scientists are working with scientists in Uruguay to acquire export permits for insects native to their country but considered problematic weeds in the Western U.S.
The environmental safety of Argentinean fly Hydrellia egeriae as a biological control agent of Egeria densa in the western U.S. was evaluated during 2015-2016. Because previous researchers indicated that the fly may feed on non-target Elodea spp., our 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. In the no-choice test, the number of eggs laid were similar on Egeria and Elodea. In the choice tests, more eggs were laid on Egeria, although a few eggs were still laid on Elodea. A third test measured the suitability of both plants for fly development. Survival was greater on Egeria compared with Elodea. A final test showed that there was no difference in egg production between the flies on the two plants, indicating that H. egeriae might be able to attack Elodea and establish in the field if it were released. Our 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.
Accomplishments
Review Publications
Castillo, J.M., Grewell, B.J., Pickart, A., Figuerora, M.E., Sytsma, M.D. 2016. Variation in tussock traits of the invasive cordgrass Spartina densiflora along the Pacific Coast of North America. Biological Invasions. 18:2159-2174.
Grewell, B.J., Skaer Thomason, M.J., Castillo, J.M., Drenovsky, R.E. 2016. Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass Spartina densiflora. Biological Invasions. 18:2175-2187.
Hopper, J.V., Pratt, P.D., McCue, K.F., Pitcairn, M.J., Moran, P.J., Madsen, J.D. 2017. Spatial and temporal variation of biological control agents associated with Eichhornia crassipes in the Sacramento-San Joaquin River Delta, California. Biological Control. 111:13-22. doi:10.1016/j.biocontrol.2017.05.005.
Madsen, J.D., Wersal, R.M. 2017. A review of aquatic plant monitoring and assessment methods. Journal of Aquatic Plant Management. 55(1):1-12.
Turnage, G., Madsen, J.D. 2017. Curlyleaf pondweed control using copper-ethylenediamine alone and in combination with endothall. Journal of Aquatic Plant Management. 55:116-119.
Madsen, J.D., Wersal, R.M., Marko, M.D. 2016. Distribution and biomass allocation in relation to depth of flowering rush (Butomus umbellatus) in the Detroit Lakes, Minnesota. Invasive Plant Science and Management. 9:161-170.
Tumage, G., Wersal, R.M., Madsen, J.D. 2017. Evaluating the efficacy of granular copper and triclopyr alone and in combination for control of flowering rush Butomus umbellatus. Journal of Aquatic Plant Management. 55:120-122.
