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Management Considerations Based on Long-Term Monitoring of Phragmites australis and Lythrum salicaria throughout Vermont

Presented by

Adrian Pierce, CWS, WPIT and Allison Slaney, PWS

March 19, 2026

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Abstract

VHB will describe NNIS monitoring efforts completed to support Vermont Wetland Permit compliance for numerous Vermont Agency of Transportation (VTrans) projects. Based on observations over 10 years at over 20 project locations, hand-pulling methods to mechanically remove common reed (Phragmites australis, “PHAU”) and purple loosestrife (Lythrum salicaria, “LYSA”) do not result in eradication or even long-lasting decreases in the areal extent of these non-native invasive species (NNIS) within impacted portions of Class II wetlands or their associated buffers. This presentation will describe the potential factors affecting the efficacy of hand-pull methodology including PHAU and LYSA population size and pre-existence of the species in or surrounding the monitoring area. We will also highlight projects for which VTrans plans to pilot alternative non-herbicidal methods of management to combat PHAU and LYSA in the 2026 growing season, with a particular focus on larger populations of each species that cannot be feasibly hand-pulled. These methods include spring beetle release to combat large populations of LYSA, mechanical shading (via tarps) over large populations of PHAU, and utilization of pollinator seed mixes.

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VTrans NNIS Monitoring �Support Distribution

VHB has provided post-construction non-native invasive species monitoring support on more than 20 projects over a 10-year span

Covering 19 towns across 11 of 14 VT counties

Range of Project Types:

Culvert replacements
Bridge work
Slope stabilization
Park and Ride
Road improvements

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�Monitoring Methodology ��Vermont Wetland Permit (VWP) Condition

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Common Reed - Phragmites australis (“PHAU”)

Listed on the Vermont Noxious Weed Quarantine List as a Class B Noxious Weed

Identifying features

Perennial grass, grows up to 15 feet tall
Distinguished from P. americanus by dull

and tan internodes during growing season

Habitat (FACW)

Disturbed areas
Wetlands and wetland edges

Reproduction

Predominantly rhizomatous growth habit;
wind dispersal of seeds

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Purple Loosestrife - Lythrum Salicaria (“LYSA”)

Listed on the Vermont Noxious Weed Quarantine List as a Class B Noxious Weed

Identifying features

Grows in clumps
Spires of 5-7 petaled purple flowers
Square, ridged stem

Habitat (OBL)

Emergent wetlands

Life cycle

One mature plant can produce up to 1 million seeds;

high germination rate

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Factors Affecting Efficacy of Hand-pull Methods

Population characteristics

Species, size, and establishment

Seed dispersal opportunities

PHAU and LYSA seed dispersal via wind and hydrochory

Presence of LYSA or PHAU populations adjacent to impacted Class II wetland or associated buffer areas

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Species, Size and Establishment of Populations

Generally, populations of PHAU cannot be controlled by hand-pulling methods alone

PHAU extremely well rooted, often challenging to successfully remove entirety of root mass
Disturbing ground to remove roots creates habitat opportunity for new/further establishment

LYSA typically more manageable

Roughly 100 stem threshold, at which point hand-pull management requires too much ground disturbance or leaves root fragments behind
Vegetative fragments (stem cuttings, broken roots) can reproduce

Populations of either species that have become established with multiple years of reproductive individuals (i.e. mature stands) may be temporarily eliminated but have likely established a seed bank

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Multiple Vectors of Seed Dispersal

PHAU or LYSA populations often observed in Year 3 or 4 of monitoring even if absence in Year 1

Presence of NNIS adjacent to monitoring areas will likely lead to establishment of population via wind or water disposal.

Herbivores and Omnivores feces dispersal

Many VTrans projects located along waterways and transportation corridors that allow for translocation of seeds into monitoring area

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Project spotlight

Bridge decommissioning project with permitted wetland and buffer impacts adjacent to White River

Extensive populations of LYSA established upstream and downstream of project likely spread through hydrochory via river overtopping, high water events/flooding

Hand-pulling of LYSA within impacted wetland and buffer not likely to result in long-lasting eradication and could contribute to streambank instability.

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Representative Project Results

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Key Takeaways

NNIS observed at more project locations during Year 5 of monitoring efforts than Year 1 at the same location

Hand-pulling may not be an effective method for NNIS control

Based on monitoring data from over 20 VTrans projects

NNIS encroachment is primarily a result of Project location and vulnerability to new or ongoing introductions/reintroductions than a direct result of construction activities

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Non-herbicidal Alternative Methods of Management

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Spring Beetle Release

Function: leaf herbivory
Application: widespread and/or well-established populations of LYSA
Two commercially available species:

Galerucella calmariensis – black margined loosestrife beetle
G. pusilla – golden loosestrife leaf beetle

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Mechanical Shading

Function: used in conjunction with removal treatment

Purpose is to suffocate established plants and prevent seed germination

Application: Large and well-established populations of PHAU
Requires thick-mil black plastic and anchors
Considerations: Can also prevent the growth/establishment of native species

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Pollinator Seed Mixes

Function: Compete with LYSA
Application: Large projects along transportation corridors, projects in areas not subject to intensive mowing regime

Requires mowing regime specific to pollinator mixes

Consideration: Used in conjunction with active methods of NNIS management, not as a stand alone alternative

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Looking Forward

Collaboration with DEC for site specific VWP permit conditions for NNIS monitoring and management

Gathering efficacy data on various other non-herbicidal methods from pilot projects

Exploring site specific risk factors and project area susceptibly for NNIS introduction

Assessing best control methods to implement based on site specifics (i.e. species, extent, proximity to sensitive resources)