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**2006 Annual Report:**

**Perennial pepperweed Control Project**

![](media/image1.jpeg){width="0.7in" height="0.8333333333333334in"}

**Sarah Janson**

**Perennial Pepperweed Coordinator**

**Nancy Pau**

**Refuge Operation Specialist**

U.S. Fish and Wildlife Service

Parker River National Wildlife Refuge

6 Plum Island Turnpike

Newburyport, Massachusetts 01950

www.parkerriver.fws.gov

**INTRODUCTION**

Perennial pepperweed (*Lepidium latifolium*) is native to Eurasia. In
the 1930's the plant was introduced to the west coast of the United
States through a shipment of sugar beet seeds. Since that time,
pepperweed has become a serious problem on the west coast infiltrating
roadsides, riversides and pasture lands. Pepperweed is present in all
states west of the Rocky Mountains.

Although pepperweed was first recorded in Peaboby, Massachusetts in 1924
and Norton, Connecticut in 1933, it has recently been observed spreading
rapidly in Massachusetts and Connecticut. In New England, infestations
of *Lepidium latifolium* are mainly found near the coast and on coastal
islands. It often occurs at the upper edges of salt marshes above the
high tide line, frequently forming dense stands. It also occurs along
highways, where it grows in disturbed areas near roads. In 2006,
pepperweed was confirmed in New Hampshire.

The state of Connecticut recently classified pepperweed as a noxious
weed. Without the natural checks on its growth which exist for
pepperweed in its native habitat, the plant has been growing and
spreading at an alarming pace in the United States. After only a few
seasons, a patch of pepperweed can grow into a dense, monoculture stand.
These stands are thick enough to shut out all light to the soil beneath
them and dominate water and nutrient supplies which prevents the growth
of native species. Pepperweed stands compete against native salt marsh
vegetation.

Perennial pepperweed is able to spread both vegetatively by rhizomes and
by seed. The root structure of pepperweed is extensive, penetrating at
least 60 cm into the soil. Root fragments as small as 2.5 cm are able to
re-sprout and grow into a multi-stemmed plant. Pepperweed is a prolific
producer of seeds which can float though water ways and distribute on
the marsh surface.

Perennial pepperweed has been observed on the Parker River National
Wildlife Refuge since the 1990's. Four patches at the north end of the
refuge have been experimentally controlled for the past 2 years with the
herbicide Escort. This work shows that applications of low concentration
Escort are an effective control for pepperweed in the Plum Island salt
marsh.

The goal of this project in the 2006 field season was to identify and
map areas of pepperweed infestation along the Plum Island Turnpike in
Newbury and on the Parker River National Wildlife Refuge, and to remove
the pepperweed by mechanical means and herbicide application. Removing
pepperweed off refuge along the Plum Island Turnpike is intended to
create a buffer zone to keep further pepperweed infestations from
developing on the refuge.

**METHODS**

Areas of pepperweed infestation were identified visually and landowners
were contacted by certified mail. Since the majority of the infestations
on the turnpike were located in the town of Newbury, a notice of intent
was filed with the conservation commission to gain permission to work in
wetland buffer zones to remove invasive plants and apply herbicides.
Once permission was granted from town officials and landowners, off
refuge areas were mapped using the Weed Inventory Management System
(WIMS) database, recording area affected and percent cover of
pepperweed. Working in partnership with Massachusetts Audubon Society,
we recruited volunteers for pepperweed removal through schools,
community networks, press releases, newspaper articles and word of
mouth. The Gulf of Maine Institute (GOMI) group adopted pepperweed
control as their mission and recruited the majority of the volunteers
for the project.

We used two methods to control perennial pepperweed:

> [Pulling]{.underline}
>
> Volunteers were recruited and trained to assist with pepperweed
> pulling because removal is labor intensive. At sites selected for
> pulling, all visible pepperweed including bolting stems and rosettes
> were removed by pulling out the stem with as much root as possible.
> All pulled sites were revisited in late August, and any regrowth was
> pulled for a second time. Since pepperweed can easily re-grow from
> small root fragments, we dried the pulled stems and roots on a black
> top surface for at least 7 days. The dry stems and roots are scheduled
> to be burned in January 2007.
>
> [Herbicide Application]{.underline}
>
> For dense, monotypic stands on the Refuge, staff applied the herbicide
> Escort, at 0.03% solution, via backpack sprayer in July and early
> August while pepperweed was in flower. In an earlier pilot experiment,
> this method was found to be 100 percent effective the first year and
> continued to control pepperweed for 2-3 years after application.

**RESULTS & DISSCUSSION**

Forty-three properties were identified as having perennial pepperweed
along the Plum Island Turnpike. We sent letters via certified mail to
thirty-three landowners for permission to map and remove pepperweed on
their property. Nineteen landowners responded granting permission to
work on their property and one denied permission. A total of 69
individuals volunteered to pull pepperweed in the months of June and
August. Eight of these volunteers helped more than once. Several groups
were involved including the Gulf of Maine Institute Teams from
Newburyport and Lowell, Groundwork Lawrence and First Year Student
Outreach from Boston University as well as Massachusetts Audubon members
and Newburyport high school students. Refuge staff also participated in
pepperweed removal.

On the Turnpike, nine pepperweed sites were pulled by volunteers over
six work days in June. Pepperweed was pulled from over 4,913 square
meter area of the Turnpike and created a 1000-meter continuous stretch
of pepperweed-free land along the south side of the Plum Island
Turnpike. Volunteers donated approximate 220 hours to pull more than
3,000 pound of pepperweed from this area. These sites were revisited in
late July and August to remove any overlooked or re-sprouted pepperweed.

Forty-six pepperweed patches were identified and mapped in the Parker
River National Wildlife Refuge. The greatest density of sites was at the
north end of the refuge but patches were found as far south as the Stage
Island Pool. Five patches were identified near the Nelson's Island
parking lot, at the west side of Plum Island Sound. The patches varied
greatly in stem number and size, probably correlated to time of
infestation. Small infestations of 3-10 stems were identified near the
Stage Island and Bill Forward Pools at the south end of the Refuge.
Larger patches of \>500 stems were found at the north end of the Refuge
near the Gatehouse and Lot 1. All Refuge pepperweed sites were treated,
31 by hand pulling and 15 by herbicide application. These sites require
monitoring in coming years to ensure complete eradication. The entire
refuge should be surveyed annually to identify and eliminate new
infestations.

Although progress to create a pepperweed firebreak along the Plum Island
Turnpike has begun, a lot of pepperweed remains along the roadside.
Control efforts in coming years should continue to remove pepperweed,
identifying sites prime for herbicide application. Sites which have been
treated should be monitored in the next growing season to assess the
success of mechanical removal and herbicide application, with special
attention to the sprouting rosette form of pepperweed.

In coming years, the geographic extent of the control effort should be
expanded to include the northern end of Plum Island, where new stands of
pepperweed were observed. Surveys could be completed along the eastern
shore and around The Basin. Additionally, new pepperweed patches are
being found at alarming rates throughout the marshes in Plum Island
Sound, indicating that the seeds and plant materials are being
transported through water. Long term control and eradication of
pepperweed will require a control program for the entire Great-Marsh/
Merrimack River watershed.

Comparative Photos of Habitat Pre and Post Treatment with Herbicide

![](media/image2.jpeg){width="5.751388888888889in"
height="4.317361111111111in"}

Pre-treatment, taken in July 2005

![](media/image3.jpeg){width="5.745138888888889in"
height="4.309027777777778in"}

Post-treatment; taken 1 year after treatment of 0.05% Escort in July
2006

![](media/image4.jpeg){width="5.688888888888889in"
height="4.266666666666667in"}

Pre-treatment- close up shot, taken in July 2005

![](media/image5.jpeg){width="5.620138888888889in"
height="4.215277777777778in"}

Post-treatment-close up shot; taken 1 year after treatment of 0.05%
Escort in July 2006

A big thank you for our **PEPPERWEED PULLERS!**

Lowell GOMI Team

Kristin McCauley (Contact)

Erica Dupras

Becky Gordon

Sarah Gordon

Kavik Desai

Maitrik Desai

Newburyport GOMI Team

John Halloran (Contact)

Anna

Nicola

Katrina Turner

James Donahue

Tim Keane

Scott

Darin

Max

Jim

Jan Smith

Abigail Gabrielse

Jennifer McCall

Sam Toolan

Philip Arets

Nico Osborne

Elizabeth Waters

Derek Stehlin

Lynette Leka

Paul Janson

Diane Janson

John Halloran

Katrina Turner

Mawra Welch

Laura Fallon

Liz Southwath

Patrick Thomas

Peter Phippen

Emma Rosenbaum

Kate de Stadler

James Donahue

Groundwork Lawrence---20 volunteers

First Year Student Outreach from BU---15 volunteers