Topic Index | Contact Us | Search

Ecology home > Environmental Assessment > Monitoring > Aquatic Plant Monitoring

Mattoon Lake, located near the town of Ellensburg in Central Washington, was selected as a site to study Eurasian watermilfoil control using weevils native to North America.

Aquatic Plant Monitoring

Contents

• Introduction
• What are invasive non-native plants?
• What Ecology’s Environmental Assessment Program is doing about aquatic invasive non-native plants
• Annual Washington State Aquatic Plant Survey
• Special projects
• Who to contact for more information

Introduction

Freshwater aquatic plant monitoring is conducted within the Department of Ecology’s Environmental Assessment Program. The monitoring program’s purpose is to track aquatic plant community changes in lakes and rivers throughout the state, concentrating on invasive non-native species such as Eurasian milfoil. In the last several years targeted research projects have also been undertaken. The aquatic plant monitoring program was established as part of the Freshwater Aquatic Weed Program in 1991. This program provides expertise on aquatic plant issues and a source of grant money (see Aquatic Weeds Financial Assistance Information) for local invasive aquatic plant management projects.

What are invasive non-native plants?

Invasive non-native plants have been introduced to Washington either accidentally or on purpose by humans. They evolved in other parts of the world, and are brought to this region without natural enemies such as plant-eating insects and diseases that normally keep their growth in check in their homeland.

The aquatic invasive plants found in Washington were all originally brought here as ornamental plants for aquariums or water gardens. These ornamental plants tend to be naturally hardy and able to withstand the tough growing conditions found in aquariums. Thus, when they are introduced to Washington’s waters, they often thrive and out-compete native plants.

What Ecology’s Environmental Assessment Program is doing about aquatic invasive non-native plants

Washington state has a State Noxious Weed Control Board that, among other things, maintains lists of the most threatening invasive non-native plant species. (For more information on the list and aquatic plants included see Overview of Noxious Freshwater Weeds in Washington.

The listed aquatic weeds that are monitored by Ecology include:

Also see Invasive Nonnative Freshwater Plants for additional information on many of these species.

Several research projects have been undertaken to further our knowledge of aquatic plant distribution and to investigate various control methods for aquatic weeds. These are described in more detail below:

• Washington State Aquatic Plant Survey Database
• Research projects on:
  • Use of 2,4-D for selective control of an early infestation of Eurasian watermilfoil in Loon Lake, Washington
  • Impact of endothall on the aquatic plant community of Kress Lake, Washington
  • Use of diquat to control Brazilian elodea in Battle Ground Lake, Washington
  • Use of fluridone to control Eurasian watermilfoil and Brazilian elodea in Loomis Lake, Washington
  • Use of triclopyr to control Eurasian watermilfoil in Capitol Lake, Washington
  • Population variations and augmentation of the milfoil weevil, Euhrychiopsis lecontei, a potential biological control agent for Eurasian watermilfoil
  • Population dynamics of curly leaf pondweed and Eurasian watermilfoil during one year in the Columbia River (Crescent Bar).

Washington State Aquatic Plant Survey

Every year, we conduct site visits to identify aquatic plants, evaluate plant community structure, and detect the existence or potential for problems, particularly as they relate to invasive non-native aquatic plants. Results of these surveys can be accessed here online.

Or, download database file (325 kilobytes zip file, Microsoft Access 2002 format).

Online results are current through survey-year 2007.

Special projects

Research project on the use of 2,4-D for selective control of an early infestation of Eurasian watermilfoil in Loon Lake, Washington

This project was undertaken in 1998 and 1999 on Loon Lake in Stevens County. It was summarized and published in the Journal of Aquatic Plant Management. The whole article can be accessed online at http://www.apms.org/japm/vol39/v39p117.pdf. The following abstract is taken from this publication:

A patchy distribution of Eurasian watermilfoil (Myriophyllum spicatum L.) in Loon Lake was treated with the herbicide 2,4-D during July 1998. Aquatic plant biomass and frequency data were collected before treatment, and six weeks and one year after treatment. Aqueous concentrations of 2,4-D increased to 1 to 2 mg/l within one day of treatment, and were below detection limits by one week after treatment. Macrophyte data were analyzed to assess the herbicide's impacts on Eurasian watermilfoil as well as the rest of the aquatic plant community. Results showed a significant decrease in Eurasian watermilfoil biomass and frequency in treated areas 6 weeks after treatment, which continued through the one year post-treatment samples. No other plant species were significantly affected by the herbicide application.

Research project on the impact of endothall on the aquatic plant community of Kress Lake, Washington

Kress Lake is a small lake formed in an abandoned gravel pit in Cowlitz County (southwest Washington). This project was undertaken in 2000 to investigate the herbicide endothall's impact on both the noxious weed Eurasian watermilfoil and the native plant community. Monitoring continued until 2003 and the results were published in the Journal of Aquatic Plant Management in 2004. In 2005 additional plant frequency data were collected and were not published, but are described below.

The following is the abstract from the publication. The whole paper can be accessed on the Aquatic Plant Management Society website http://www.apms.org/japm/vol42/v42p109.pdf.

A dense mat-forming population of Eurasian watermilfoil (Myriophyllum spicatum L.) was interfering with fishing and recreation in a small western Washington lake. A low concentration (1.5 mg/L active ingredient) of the herbicide endothall formulated as Aquathol® K was used in 2000 to attempt to selectively control the Eurasian watermilfoil. Aquatic plant biomass and frequency data were collected before treatment, ten weeks after treatment and during the growing season for 3 additional years. Macrophyte data were analyzed to assess the herbicide's impacts on Eurasian watermilfoil as well as the rest of the aquatic plant community. Results showed a significant decrease in Eurasian watermilfoil biomass and frequency 10 weeks after treatment. The Eurasian watermilfoil continued to be present, but at a significantly reduced level through the remainder of the study (3 years after treatment). Of the native plant species, large-leaf pondweed (Potamogeton amplifolius Tucker.) frequency and biomass was significantly reduced after treatment. Common elodea (Elodea canadensis Rich.), muskgrass (Chara sp. Vallaint.) and bladderwort (Utricularia sp. L.) all increased significantly after treatment.

In 2005 additional plant frequency data were collected following the same methods used in the original study. A table comparing the 2005 data to the pretreatment data from 2000 is below.

Table: Percent frequency of common aquatic plants in Kress Lake pretreatment and five years post treatment. Significant differences indicated in bold (p<0.05).

There was no significant difference between the frequency of Eurasian milfoil in 2005 and 2000, so it has returned to essentially pretreatment levels.

The big leaf pondweed frequency is still at significantly reduced levels compared with before treatment. The other common native species, however, were all still found at significantly higher frequencies in 2005 than before treatment.

Research Project on the use of Diquat to control Brazilian elodea in Battle Ground Lake, Washington

The aquatic invasive non-native plant egeria (Egeria densa Planch.) in Battle Ground Lake (Clark County) was treated with the herbicide diquat in 2003. The purpose of this project was to monitor plant community changes and water quality before treatment and up to three years after treatment. There was a significant reduction in egeria frequency and biomass after the herbicide treatment. The diquat spread throughout the lake and persisted at low levels in the water column for at least two weeks after treatment. There was a slight decrease in surface water dissolved oxygen and water transparency after the herbicide treatment due to increased algae growth.

This study was published in the Journal of Aquatic Plant Management in the January 2007 issue.  Publication No. 07-03-030.

Research project on the use of fluridone to control Eurasian watermilfoil and Brazilian elodea in Loomis Lake, Washington.

In 2002 Loomis Lake (Pacific County, coastal southwest Washington) was treated with the slow-acting systemic herbicide fluridone to control both Eurasian watermilfoil (Myriophyllum spicatum) and Brazilian elodea (Egeria densa). We have monitored the aquatic plant community for three years after treatment.  The data will be finalized and published formally. If you would like additional information on the project in the mean time please contact Jenifer Parsons.

Research project on the use of triclopyr to control Eurasian watermilfoil in Capitol Lake, Washington.

In 2004 Capitol Lake (Thurston County, City of Olympia) was treated with the selective herbicide triclopyr to control a burgeoning population of Eurasian watermilfoil (Myriophyllum spicatum). Aquatic plant data were collected by Ecology before treatment, and by Thurston County after treatment. The final data were collected in 2006, and the data are being finalized and published. If you would like additional information on the project in the mean time, please contact Jenifer Parsons.

Research project on population variations and augmentation of the milfoil weevil, Euhrychiopsis lecontei, a potential biological control agent for Eurasian watermilfoil.

Background:

The aquatic invasive non-native plant Eurasian milfoil (Myriophyllum spicatum) has been in Washington State since at least 1965. Since that time it has been introduced to more than 90 lakes and reservoirs and many major rivers including the Columbia, Okanogan, Snake and Pend Oreille Rivers (distribution map).

When the distribution of an invasive non-native species reaches the proportions of Eurasian milfoil, biological control agents are often sought to aid in their management. (Biological control is the use of natural enemies such as insects to reduce the damage caused by a pest population such as an invasive non-native plant.)

The milfoil weevil (Euhrychiopsis lecontei) (a beetle in the family Curculionidae) has been implicated in causing declines of Eurasian milfoil in Midwestern and Northeastern States. This weevil is native to the northern part of the United States, including Washington (Tamayo and Grue 1996). The weevil’s native host is the native northern milfoil (Myriophyllum sibiricum), however, if the weevil is reared on Eurasian milfoil it will prefer it over northern milfoil. The weevils spend their entire life cycle on milfoil. The adults eat leaves on the growing tips, and larvae mine into the stem causing a reduction in plant buoyancy. An excellent summary of milfoil weevil life history and research is available through the milfoil biocontrol website.

During the later 1990’s Ecology’s Aquatic Weed Management Fund partially supported research on the milfoil weevil in Washington conducted at the University of Washington. Several papers have been published as a result of this work. (See list of publications below.)

As a result of the research conducted by the University of Washington and Ecology, naturally occurring populations of the milfoil weevil are known from the following locations in Washington:

Augmentation project:

During the summers of 2002 -2003 we conducted a weevil rearing and augmentation study to meet three objectives:

• to gain experience collecting, rearing, and releasing the milfoil weevil,
• to monitor the introduced milfoil weevils and aquatic plant community at a study site,
• to determine whether fish target the milfoil weevils as a new or more prevalent prey item.

Mattoon Lake, located near the town of Ellensburg in Central Washington, was selected as the milfoil weevil introduction site. It is a small, shallow, man-made lake, with a maximum depth of about 5 m (16 ft). Aquatic plants grow throughout the lake, but the dominant submersed plant in water 2-12 feet deep is Eurasian milfoil.

Through the summer of 2002 we collected adult weevils from Stan Coffin Lake in Grant County each week for about 12 weeks by snorkeling (once from near-by Burke Lake). We also continued to monitor weevil activity in Stan Coffin Lake until they abandoned the plants for their over-wintering habitat on shore. The weevils were still evident, though in reduced numbers, in mid-October with a water temperature of 55˚ F (13˚ C). By November 1, 2002, the weevils were very difficult to locate with only one weevil found in 20 minutes of snorkeling; the water temperature was 43˚ F (6˚ C).

A total of 705 adult weevils were collected from M. sibiricum (northern milfoil) plants throughout the summer of 2002. The peak collection time was the end of July through the end of August, when an experienced snorkeler could collect at a rate of about one weevil per minute. Often there were two or three weevils per milfoil stem, a density thought to be great enough to control M. spicatum growth (and, in fact, Eurasian milfoil is present in Stan Coffin lake, but difficult to find).

The captured weevils were kept in aquariums at the Fish and Wildlife Department buildings in Yakima for between 5 and 14 days. (see weevil rearing document for more details on raising weevils). At the end of the rearing period we counted the numbers of eggs, larvae and adults. Then the weevils and their progeny were introduced into Mattoon Lake at designated release sites. From a small boat, we wound the milfoil pieces on which the weevils were clinging around existing surfacing milfoil at two sites in the lake. This cycle of rearing and release continued throughout the summer, and by the end of summer a total of nearly 3,000 weevils of all life stages had been released.

To monitor the milfoil weevil population at Mattoon Lake, two methods were used: a qualitative check for weevil damage on milfoil plants, and quantitative sampling at points throughout the lake. Prior to the initial introduction of milfoil weevils, Mattoon Lake was inspected for an existing weevil population. The lake was checked again using the same methods in early September of 2002 toward the end of the stocking period. We repeated the weevil monitoring in 2003, 2005 and 2007.

For the qualitative check for weevil damage, experienced weevil-hunting snorkelers conducted three 20-minute visual searches in selected areas of the lake, including those sites chosen for weevil introduction. No signs of weevils or weevil damage were observed during either of the inventories in 2002, 2003 or 2005.  In 2007 weevils were abundant, and extensive damage tothe Eurasian milfoil was evident.

The quantitative data were obtained by collecting milfoil stems from locations are the lake.  In the lab each plant was inspected for presence of all weevil life stages and weevil damage using a dissecting microscope. We found no evidence of an established milfoil weevil population from plants collected during either of the dates in 2002, 2003 or 2005; although we did find evidence of meristem damage and leaf grazing, especially on the lower branches, likely caused by other herbivorous insects.  In 2007 milfoil weevils and stem damage characteristic of milfoil weevil grazing were observed.

To monitor the aquatic plants at Mattoon Lake, both aquatic plant biomass and frequency data in Mattoon Lake were collected before initial weevil introductions occurred. These data have been collected annually for several years to monitor for changes in these parameters as weevil densities (we hope) increase.

There was no sign of weevil establishment in Mattoon Lake at the end of 2002. In conjunction with this project, the Department of Fish and Wildlife had conducted a fish population inventory of Mattoon Lake in spring 2002. That inventory revealed that Mattoon Lake has a very dense population of small pumpkinseed sunfish (Divens 2003). Other studies have found that pumpkinseed and bluegill sunfish will eat milfoil weevil adults (Sutter and Newman 1977; Lord et al 2003). Thus, we suspected that the pumpkinseed in Mattoon Lake suppressed widespread establishment of the weevils we introduced.

For our work in 2003 we decided to set up a fish exclosure cage similar to one Dr. Ray Newman and his students had used in similar studies in Minnesota (Newman 2003). We built the 10 ft x 10 ft exclosure frame from pvc pipe and surrounded it with fish netting suspended by floats at the top and held in place with weights at the bottom to keep fish out of the study area. We then set traps and angled to catch any fish that were caught inside the exclosure.

Over the course of the summer 2003 we collected, raised and released 1,670 weevils of all life stages into the exclosure, and another 815 outside the exclosure at the southwest end of the lake by tying milfoil fragments with weevils onto rooted milfoil (see weevil rearing document for details). We observed adult weevils in the exclosure from previous releases toward summer’s end, but the population never established enough to control the milfoil. At the end of summer (September 24, 2003) we removed the exclosure. In the summer of 2004 we snorkeled where the exclosure had been and found a few adult weevils in the area, however, again they did not seem to persist or establish in numbers great enough to control the milfoil.

While we were encouraged to find that weevils did survive in Mattoon Lake, we were disappointed they did not establish at the levels high enough to impact milfoil growth until 2007. The Department of Fish and Wildlife did another fish inventory on Mattoon Lake in October 2007.  They are currently analyzing the data to assess changes that could have allowed the milfoil weevil population to expand.

Fish community and diet analysis

This part of the project was undertaken in cooperation with the Washington Department of Fish and Wildlife; a brief summary is provided here. The fish community was sampled at the end of May 2002 before any weevil stocking had begun. The species composition of the community was assessed by electroshocking. At this time stomach samples from each species that reached a size big enough to consume adult weevils as part of their diet (i.e. the sunfish, bass, perch and trout) were also collected. The stomach contents from a subset of the fish caught by electroshocking were flushed into a sample container and preserved in ethanol. Samples were analyzed in the lab by a contracted macroinvertebrate specialist. The fish community was again assessed in fall 2007 without the diet analysis.  Those results will be reported when they are finalized. 

Correlation between fish communities and milfoil weevil populations

Ecology is undergoing data analysis on studies comparing fish communities with populations of invertebrates that live on aquatic plants in general, and with herbivorous insects in particular. The correlations between high populations of sunfish such as bluegill and pumpkinseed and low levels of aquatic herbivorous insects are promising. As these data are analyzed they will be published and added to this website. If additional information is desired in the mean time please contact Jenifer Parsons.

Citations

Divens, M. 2002 Washington Department of Fish and Wildlife, Spokane Office. Personal communication.

Hanson, T., C. Eliopoulos, and A. Walker. 1995. Field collection, laboratory rearing and in-lake introductions of the herbivorous aquatic weevil, Euhrychiopsis lecontei, in Vermont: Year 2. Vermont Department of Environmental Conservation, Waterbury, VT. 41 pp.

Lord, P.H., J.G. Wells, and A.L. Armstrong. 2003. BFS Technical Report #21: Establishing a connection: a survey of Eurasian water-milfoil (Myriophyllum spicatum), its insect herbivores and fish in eight Madison County lakes. Suny Oneonta Biological Field Station; Cooperstown, NY. 46 pp.

Newman, R. 2003. University of Minnesota. Personal communication.

Sutter, T. J., and R. M. Newman. 1997. Is predation by sunfish (Lepomis spp.) an important source of mortality for the Eurasian watermilfoil biocontrol agent Euhrychiopsis lecontei ? Journal of Freshwater Ecology 12: 225-234.

Tamayo, M. and C. Grue. 1996. Evaluation of the native status in North America for the weevil Euhrychiopsis lecontei. University of Washington cooperative Fish and Wildlife Research Unit. Seattle, WA

List of publications on weevils in Washington:

Tamayo, M. and C. Grue. 2004. Developmental performance of the milfoil weevil (Coleoptera: Curculionidae) on watermilfoils in Washington State. Environ. Entomol. 33(4): 872-880.

Tamayo, M., C. Grue and K. Hamel. 2004. Densities of the milfoil weevil (Euhrychiopsis lecontei) on native and exotic watermilfoils. Journal of Freshwater Ecology 19(2): 203-211.

Tamayo, M., C. Grue, and K. Hamel. 2000. The relationship between water quality, watermilfoil frequency, and weevil distribution in the State of Washington. Journal of Aquatic Plant Management 38: 112-116.

Tamayo, M. 2003. Developmental performance, abundance and habitat of the milfoil weevil, Euhrychiopsis lecontei, in Washington State. PhD Dissertation. University of Washington Cooperative Fish and Wildlife Research Unit. Seattle, WA

Population dynamics of curly leaf pondweed and Eurasian watermilfoil during one year in the Columbia River (Crescent Bar).

The objective of this project was to see if the non-native plant curly leaf pondweed (Potamogeton crispus) was a significant component of the plant community and if so, to see how the population changed over the growing season.

Crescent Bar is located on the Columbia River in central Washington. It is about 20 miles downstream of Wenatchee in Grant County. It is a resort area with a small marina and boat access located on the protected side of an island formed by a large sand bar. It is a heavily used recreation area, particularly in spring and summer months. Sampling stations were located along three transects, one at the north end of the island close to the main river, the second was near the boat launch/marina and the third was on the back (east) side of the island.

Sampling began in early April 2005, and continued monthly through late October 2005. Sample points were located approximately 20 meters apart along the transects and returned to each visit by using a GPS (Global Positioning System). At each point samples were collected by tossing a sampling rake four times and recording the species collected with each toss.

Below is a table of the percent of rake samples where the most common species were present.

These data indicate that at least in this rather confined area of the Columbia River, the curly leaf pondweed was at its greatest frequency in June and July, then declined to the point of not being collected in any of the samples by fall (though it could still be found as a rare small plant in places other than the sample points, so it wasn’t completely gone). This is similar to what has been found in the Midwest (Catling and Dobson 1985), although the die-off appeared to happen a little later in the summer here. This could be due to cooler water temperatures in the Columbia River than in areas studied in the Midwest (Madsen 2005) (surface water temperature was; early June 14° C, early August 20° C). The Eurasian milfoil was most frequently collected toward the end of the summer, but its distribution was patchy. The dominant plant throughout the summer was American waterweed (Elodea canadensis), a common native species. Another native plant, coontail (Ceratophyllum demersum), was common and tended to dominate in the deeper water. In general, the plant growth in the study area was quite dense, especially in July and August, but it was a mix of the above four common species and other less common native plants. It was not a monoculture of any one of them.

Citations

Catling, P.M., I. Dobson. 1985. The biology of Canadian weeds 69 Potamogeton crispus L. Canadian Journal of Plant Science 65: 655-668

Madsen, J.D. 2005. Mississippi State University. Personal communication.

Who to contact for more information

• Jenifer Parsons, Environmental Assessment Program, Central Regional Office

Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.

Copyright © Washington State Department of Ecology Contact Us | Privacy Notice | Site Info

Information for Ecology staff