Download White Fragrant Waterlily

ADDENDUM 1 TO LONG LAKE MANAGEMENT PLAN
IPM PRESCRIPTION FOR CONTROL OF WHITE FRAGRANT WATERLILY
(Nymphaea odorata)
Note to Reader: References to Lake Lawrence with the Long Lake Prescription are intentional,
because both lakes are similar in function and size and they have similar aquatic plant
management issues and are nutrient rich environments.
Growth habits and nuisance created: White fragrant waterlily (Nympaea odorata) is a nonnative floating-leaved perennial aquatic plant. The plant has a stiff stem with a round, thick,
floating leaves and white flowers. It propagates via rhizomes which spread through organic
sediment in shallow areas. These lilies can out compete native vegetation and have been
demonstrated to be allelopathic (produces chemicals which thwart growth of other plants).
White fragrant waterlily was brought here from the eastern US and is now present in many lakes
in our region. Yellow waterlily (Nuphar spp.), a native lily species, is also present in the lake but
is generally confined to a shallow band along the shoreline and poses much less nuisance and is
not proposed for control under this Plan.
Fragrant waterlily propagates through: (1) rhizomes spreading from existing beds into adjacent
suitable areas, (2) flowers that produce many seeds and (3) pieces of rhizomes that escape during
manual or mechanical removal are also viable.
Propagation as an ornamental includes selling the rhizome pieces that are about 4 inches in
length (1). The spread of lilies through rhizomes is fairly rapid, for example; a planted 4”
rhizome will spread to cover about a 15-foot diameter circle in five years (1).
Small beds of lilies interspersed with open water are useful habitat for fish and wildlife.
However, researchers have found that large beds of lilies with dense surface canopies can impair
the habitat and recreational value of the lake and are commonly a target of aquatic plant control
efforts in lakes throughout Washington State.
The habitat value is reduced when the floating leaves cover the entire lake surface. Under this
condition, virtually no oxygen is supplied into the water column and alter the water pH. In
addition, large, dense mats preclude wind-mixed oxygen, which is another major oxygen source
in the lake. This oxygen depletion reduces habitat for fish within the prime littoral zone of the
lake (the lighted and vegetated shallow areas which are critical to many species and life stages).
The large dense beds are also difficult for waterfowl to utilize.
Recreation value is significantly impaired where lily beds grow along residential and recreational
shoreline areas. Lake access and use for swimming, boating or other activities is essentially
blocked by the dense surface mat of vegetation.
Following lily removal, submerged aquatic plants such as pondweed typically colonize these
prime aquatic habitats. The typical result is generally an aquatic plant population which is more
beneficial to wildlife and of less nuisance to human use of the lake, particularly where a lake is
free from other highly invasive submerged aquatic plants like Eurasian Watermilfoil.
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Nuisance lily growth at Long Lake: In recent years, lilies have gradually spread to extensive
near-shore areas of Long Lake. Examination of aerial photographs taken in summer months
indicate that lilies have spread from a few patches along the lake margin in 1993, to scattered
beds over a wider area of the lake in 1996, to dense beds in many areas of the lake in 2005. The
spread of lilies in Long Lake as depicted on aerial photographs is shown on Attachments 1-3.
Estimated coverage by lilies is now approximately 40 acres. About 176 acres of the 330 acre
lake was occupied with aquatic vegetation of various types in 2005 with floating-leaved plants
(predominately white lilies) comprising about 40 acres (25%) of the total coverage.
Some of the native lily areas are primarily utilized for habitat by aquatic and avian species,
particularly the northern-most cove. However, much of the infested shoreline is in longestablished residential and recreational areas. These uses are significantly impaired by the nonnative lilies. Research by the University of Washington, School of Fisheries included detailed
assessment of water quality in various vegetated and open-water areas of Long Lake. In shallow
areas of the lake, dissolved oxygen content appears to be associated with the type of plant cover.
Sites with floating-leaved fragrant waterlily had low sub-surface dissolved oxygen (DO)
concentrations at the lake surface. In contrast, sites with submersed plants (like pondweeds) had
high DO due to plant growth and respiration (2).
The phenomenon of oxygen depletion beneath dense mats of aquatic vegetation has been
documented in lakes across the State. Attachment 4 illustrates oxygen depletion below a mat of
the floating leaved plant Brasenia. As plant cover increases in the summer, oxygen drops below
the fishery minimum of 4 ppm throughout the summer months making it unsuitable for fish life.
As summarized in Attachment 5, caged fish placed within a lily bed had 100% mortality within
12 hours.
At Long Lake, lilies have reached the injury level in many areas of the lake. There is significant
loss of habitat value and lake access and recreational use by residents and the public. The nonnative plant will continue to spread in the shallow areas of the lake if no action is taken.
The proposed lily control area at Long Lake is about 40 acres in size. Specific areas that will not
be treated will be identified collaboratively with the Long Lake Steering Committee and
Thurston County.
History of previous control efforts at Long Lake and Lake Lawrence: Thurston County Pest
and Vegetation Management policy emphasizes the use of physical, mechanical and cultural
techniques for control of nuisance vegetation. At both Long Lake and Lake Lawrence,
substantial effort has gone into attempting to get effective lily control through use of these
preferred techniques. In the section below, the various techniques available for lily control are
briefly described following by a summary of their application at Long Lake and Lake Lawrence.
MECHANCAL TECHNIQUES:
Harvesting: Lilies can be cut underwater by harvesters on a floating barge or by hand-held tools.
Control is provided until the plant sends another leaf to the surface. The extensive energy stored
in the lily tuber allows rapid regrowth of harvested lilies. Although the pads will initially be
smaller, in shallow areas the same number of lily pads will generally regrow within several days
of harvesting during the mid-summer season.
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At Lake Lawrence, aquatic weed harvesting was conducted from 1986 – 1989 with large bargemounted weed harvesters. At Long Lake aquatic week harvesting was conducted from 19861990 and again 1995 through 2005. While temporary control was obtained, the lilies regrew
rapidly from the large rhizomes in the lake sediment. Within a few days, lilies once again were
on the lake surface in shallow areas. In addition, the equipment could not operate effectively in
the near shore and dock areas infested with nuisance lilies.
Digging: At Long Lake lily rhizomes can also be removed from the sediment. This is a more
labor intensive method than harvesting and provides longer control. Removal can be performed
by hand on very small areas. Some property owners report success in repeated cutting and
digging of rhizomes to prevent spread from adjoining areas. However this is a very labor
intensive action with limited success. The results are not consistently predictable, mixed
successes are reported.
To control lilies in larger areas, barge-mounted equipment is used to dig rhizomes from the
sediment by digging with a bucket or rotovation. Sediment disturbance is created by mechanical
removal of lily rhizomes. However, the sediment settles back to the lake bottom within a few
hours (3).
At Lake Lawrence, mechanical removal of lily rhizomes was conducted via a volunteer-operated
program in 1994 and 1995. Two County-owned harvesters were utilized, one with a backhoe
arm to dislodge the lily rhizomes from the sediment and the other with a harvesting head to
collect the floating rhizomes. The second harvester is then off-loaded through a conveyor into a
dump truck for removal from the lake. In 1994, 13 volunteers provided over 500 hours of
volunteer work. They removed over 300 tons of lily rhizomes from several acres of the lake.
In 1995, the volunteers assessed the success of their efforts. Following are their conclusions:
1. Long-term control was not obtained. In the controlled areas, lilies were less dense but
still present. While longer control is obtained than with harvesting, lilies in the control
areas are anticipated to regrow fairly rapidly to the original density if no other control is
applied.
2. The technique appears to be spreading the nuisance plant. A very troubling problem is
that some of the dislodged rhizomes appear to be floating into new areas, sinking to the
bottom, and creating new beds of the nuisance plant. It is simply impossible to capture
all the rhizomes following digging. This has led to increasing negative and divisive
reaction from property owners who previously had no lilies or very few lily problems.
3. The technique is very labor intensive. The project would have been infeasible due to
expense if volunteer labor was not utilized. In 1995, it was becoming increasingly
difficult to staff the volunteer effort.
Rotovation: At Long Lake a small experimental rotovation project was conducted in 1993.
Long-term control was not achieved and appears to spread the lily while increasing turbidity due
to significant sediment disturbance.
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CULTURAL TECHNIQUES:
Bottom Barrier: Bottom barrier (also known as bottom screens) can be secured to the lake
bottom to cover areas of nuisance aquatic vegetation. This technique is applicable only to
localized control of relatively small areas. If the application is successful, a high level of control
is provided in the small areas. The results are not consistent, mixed successes are reported.
At Long Lake in 2003, a demonstration project in cooperation with a private property owner,
used poly polypropylene fabric in about 6-8 feet of water. A large sheet of fabric was laid by
divers and was weighted with sand bags. At Lake Lawrence, several property owners attempted
use of bottom barriers in the late 1980s. Polypropelene fabric was attached to wooden frames
usually 4’x8’ and placed on the lake bottom in the near-shore area and held in place by sandbags
or other means.
The results of lily control by using bottom screens were marginal. The large lily leaves would
push through slits in the fabric, which were essential to vent gases created in the organic lake
sediment. The screens were also very difficult to install in the highly flocculent sediment.
Dredging: Another cultural control is to deepen the lake to make conditions less favorable to
lilies. Deeper water will tend to favor submerged plants like pondweeds as opposed to water
lilies. At Lake Lawrence, dredging has been the subject of extensive studies and design reports.
At this time, the high cost of dredging remains a key unresolved issue. Long Lake faces the
same challenges in addition to those challenges that result from intense urbanization reducing
options to stage essential dredging equipment.
BIOLOGICAL TECHNIQUES:
There are no available biological control techniques for lilies. Grass carp, and increasingly
common biological control technique for aquatic plants, will not forage on lilies unless virtually
no other food is available.
CHEMICAL TECHNIQUES:
The aquatic herbicide Rodeo (glyphosate) is used for chemical control of lilies and other
floating-leaved plants. The material is applied to the leaves and is rapidly translocated through
the plant, providing systemic control of the nuisance vegetation. The material is generally
sprayed from boat-mounted equipment. Careful application to the leaf surface allows clear
demarcation of control areas and habitat areas (in contrast to aquatic herbicides which are
applied to water.)
Treatment is made in the mid-summer (July) growing period, when the plant is storing energy in
the rhizomes for the next growing season. Follow-up spot treatment is commonly required to get
complete control within the target area. Excellent control of lilies within the target area is
generally obtained with glyphosate.
One potential drawback to chemical control of lilies may be the creation of large mats of
decaying lily rhizomes following treatment. Lily beds are composed of intertwined rhizomes.
When a large area of lilies is controlled, decay may create gases which trigger mats of rhizomes
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to rise to the surface. Large mats created by herbicide treatment may persist for a season or
longer.
Control Plan
Goal: The goal of the control plan is to eradicate fragrant waterlily in residential, recreational
and habitat reserved areas of Long Lake. The areas where lilies are growing, illustrated on
Attachment 3, cover about 40 acres. The treatment program is designed to maximize
recreational and habitat values of the lake and maximize the effective period of the herbicide
treatment.
Injury and Action Levels: Injury levels are reached when lilies cover most of the water surface
in residential or recreational shoreline areas. When the injury level is reached water contact
recreation is precluded, boating is blocked, and habitat degradation occurs due to large dense
surface mats of vegetation such as the white fragrant waterlily. Control activities (action) should
occur at a time that will prevent the injury level from occurring.
Action activities should occur when the lily plant is initially colonizing designated control areas.
Control is most effective and causes the least environmental impact at an early level of
infestation in the designated areas. Eradication from the lake is not an option; rather it is the
management goal, as the plant is widespread. However, in an infested area, the plant spreads
within several years closing open water areas and forms large dense mats.
Treatment of the habitat reserve areas is included to improve habitat by: (1) allowing more
favorable native submersed aquatic macrophytes to grow in areas where lilies only grew before;
(2) replacing dense surface mats of lilies with sparse coverage will create more “edge effect”
(desirable for habitat); and (3) to reduce reinfestation of residential and recreational areas. The
intent is to maximize the longevity of the lily treatment while improving fish and wildlife habitat
and recreational use.
Treatment: Based on the demonstrated nuisance posed by non-native lilies and the extensive
unsuccessful attempts to utilize non-chemical techniques at both Lake Lawrence and Long Lake,
the following plan is proposed.
A.
Years one through four – Herbicide treatment and public education:
Herbicide Treatment: The systemic aquatic herbicide glyphosate (common trade name Rodeo)
will be used to remove nuisance lilies in the control areas. A surfactant is required for effective
treatment of the waxy lily leaves. The surfactant to be used will be the product preferred by the
Washington Department of Ecology – LI 700. This is a non-ionic penetrating surfactant.
Timing: The best timing for controls is after July 15 for both effectiveness in treating the lily
and to avoid conflict with duck broods.
Spot retreatment following the recommended timing is commonly required the following year
for plants which were missed in the initial application and regrowth from rhizomes and seeds.
Nearly 100% control within the target area is anticipated after the initial and follow up spot
treatments.
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Application techniques will minimize the drift and impact to non-target plants and
organisms. Emergent wetland vegetation adjacent to the lily control areas are important plants
to protect from the control effort. Also, Carex composa, a sensitive plant that was found in
1945, may still be growing along the lakeshore. Therefore, application techniques will be
utilized to prevent non-target impacts. The application method usually used in this type of
treatment is to apply the product to the surface of the floating leaves via a boat-mounted spray
gun. In areas near the shoreline, techniques such as spraying from the shoreline side of the target
area into the lake by positioning the boat near the shore of the treatment area or by the applicator
working on foot along the shoreline. This allows accurate treatment of control areas while
avoiding treatment of emergent vegetation which is valuable for habitat. Another application
technique that will minimize drift is to apply during calm wind conditions of under 5 mph.
Maximum label rate for Rodeo is 7 1/2 pints per acre. Typical rates for lilies are often lower
(approximately 4 pints per acre). Rodeo contains 53% active ingredient, which is added to lake
water in the spray tank. In typical application to lilies, 1-2 ppm active ingredient is applied.
The treatment areas will include approximately 10 surface acres per year of the lake where the
lilies grow except for buffers that will be identified collaboratively with Long Lake Steering
Committee and Thurston County. A limited annual control action intends to minimize the
potential of floating tuber-mats by not treating large areas in any one season.
If rhizomes rise to the surface in large mats following treatment, they will be removed by hand or
mechanically depending on the size and extent of the mats. Volunteer effort by property owners
is anticipated if action is required.
Public education: It is recommended that public education be accomplished through the current
bi-annual newsletter. The fact sheet should provide information on at least: (1) general
information about the fragrant white waterlily and the problem it has created, (2) the proposed
treatment plan, (3) the expected regrowth of other submergent aquatic plants in areas that are
currently only waterlilies, (4) issues such as County policy requirements and regulations
pertaining to aquatic herbicide applications in general.
B.
Year 5 and after – Maintenance removal of rhizomes:
Lilies will encroach into control areas from non-controlled buffer zones. In addition, a small
number of plants may survive the four-year herbicide control program. If the small initial
number of rhizomes and the germination of seeds after the herbicide treatment area are not
controlled, the plant will again spread into dense mats throughout the control area.
In residential and recreational areas of the lake only, pioneering rhizomes in Year 5, and after,
will be treated periodically as control efforts are economically feasibility and before injury levels
are exceeded. Future control actions are anticipated once every three to four years with spot
treatment. The total acreage is expected to be less than two total surface acres. This control
method is recommend based on the history for both Long Lake and Lake Lawrence, where
manual control techniques have not demonstrated successful lily control. This IMP Prescription
is consistent with County policy which emphasizes non-chemical techniques where effective.
Timing: Maintenance control of pioneering plants should occur annually during the summer
growing season following July 15.
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Monitoring and Evaluation: The success of the herbicide treatment should be evaluated in the
summer of Year 3 and again in Year 5. Photographs taken from boat and/or by GPS mapping
can cost effectively track trends in the growth of floating leaved plants such as lilies. An annual
report and evaluation consistent with County policy should be prepared by the LLMD and
submitted to the Thurston County Pest and Vegetation Advisory Committee. The report should
include at a minimum (1) the areas where the lilies were controlled, (2) the number of acres of
plants that were controlled, (3) areas of the lake where pioneering lilies are growing.
Attachments:
Attachments 1-3: 1993, 1996 and 2003 maps of the spread of lilies in Long Lake from aerial.
Attachment 4: Oxygen Depletion Beneath Aquatic Plant Surface Mats. From Pauley etal., The
Effects of Triploid Carp Grazing on Lakes in the Pacific Northwest, Washington Cooperative
Fishery and Wildlife Unit, School of Fisheries, University of Washington, Seattle, 1988.
Attachment 5: Impacts of Aquatic Plants on Water Quality – Lake Washington Caged Fish
Studies.
References:
1. Submittal to State Weed Board for listing of Fragrant Waterlily as a noxious week,
Department of Ecology, September 1995 (pending).
2. Thomas, G.L. etal., Feasibility of Aquatic Plant Control in Lake Lawrence using Triploid
Grass Carp, Washington Cooperative Fishery and Wildlife Unit, School of Fisheries, University
of Washington, Seattle 1990.
3. Thurston County Department of Water and Waste Management. Timberlake Lily Removal
Project Report – 4 pages, February 1993.
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MANAGEMENT PLAN.doc
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