NATIVE
RANGE
Southeastern Europe and southwestern Asia
DESCRIPTION
Perennial pepperweed
(synonym: Cardaria latifolia (L.) Spach), is also known as tall whitetop,
giant whiteweed, perennial peppergrass, slender perennial peppercress, broadleaf
or broadleaved pepperweed, ironweed and other names. Plants are multiple
stemmed and grow in stiffly erect masses up to 5 ft. (1.5 m.) tall, sometimes
taller. Leaves are lanceolate, bright green to gray green, and entire or
toothed. Basal leaves are stalked, up to 1 ft. (30 cm) long and 3 in. (8
cm.) wide and have serrate margins. Stem leaves are smaller, ranging from
3-10 in (7-25 cm) in length, tapered at the base, entire to weakly serrate
and are sessile to stalked. Flowering occurs from early summer to fall. Abundant
small white 4-petaled flowers are borne in dense clusters near the stem tips.
The fruits are small, flattened pods about 1/10th inch long, each containing
2 seeds (1 per chamber). Fruits remain on the plant, dropping irregularly
throughout the winter. The base of the stem is semi-woody. The roots enlarge
at the soil line, forming a woody crown. Root length is dependent on soil
tilth, but can be up to 6 feet. Roots are creeping, with new plants springing
from root sections as small as 2 inches. Seedlings, when present, have leaves
that are ovate to oblong, ¼-½ inch long, with smooth to slightly
wavy edges and a petiole approximately 1/5th inch long. Subsequent leaves
resemble first leaves, but are larger in size.
ECOLOGICAL
THREAT
Perennial pepperweed is a highly invasive herbaceous perennial.
It can invade a wide range of habitats including riparian areas, wetlands,
marshes, and floodplains. It adapts readily to natural and disturbed wetlands.
As it establishes and expands, the plants create large monospecific stands
that displace native plants and animals. It addition to impacting alfalfa
and pasture production, it has been reported to adversely affect food quality
and nesting habitat for native birds and threaten the Carson’s Wandering
Skipper butterfly. Most of the reports of habitat and food quality are
anecdotal.
DISTRIBUTION
IN THE UNITED STATES
Infestations have been reported in coastal, intermountain
and mountainous areas in New England, all the states west of the Rocky
Mountains, except Arizona. It also occurs in Canada and Mexico.
HABITAT IN THE UNITED STATES
Perennial
pepperweed occurs in riparian (stream) areas, coastal wetlands, marshes,
roadsides, railways, ditches, hay meadows, pastures, cropland, and waste
places.
BACKGROUND
Pepperweed probably
entered the U.S. prior to 1940 in a shipment of beet seed (Beta vulgaris)
from Europe.
BIOLOGY & SPREAD
Perennial
pepperweed rarely produces seedlings in the field. There is no known reason
for this, as laboratory tests have shown seed viabilities to be high. Seeds
lack a hard seed coat and lose viability rapidly, suggesting that resurgence
of a treated infestation from the seed bank would be low. The plant mainly
propagates clonally from its brittle rhizome-like roots. Roots exposed by
washouts and land disturbances fragment and move along riparian corridors
to start new infestations downstream. Roots fragmented by the mechanical
actions of land management practices increase infestation densities and facilitate
spread.
MANAGEMENT
OPTIONS
Deep-seated rootstocks make pepperweed difficult to control.
With the exception of continual flooding, no non-chemical treatments have
been found to effectively control this weed as a sole control option. Excellent
control can be obtained with a combination of herbicides and cultural practices
which fit in various control strategies, but application of the control
plan must be repeated numerous times to obtain lasting management. Slow
recovery of desirable plants is often an issue when combating pepperweed.
Revegetation with desirable species may be necessary to restore the landscape.
Perennial roots can also remain dormant in the soil for several years, thus
intense early detection monitoring and removal are the best control measures
for perennial pepperweed. Sources of infestations should also be located and
eliminated to prevent future infestations. Treating pepperweed with herbicides
at a non-optimal time of year (e.g. other than at flower bud) is ineffective,
as the roots, where carbohydrates are stored, are not affected by the spray
and new plants will rapidly resprout.
The most effective control regimes
are:
- Spring grazing with subsequent
chlorsulfuron or imazapyr application at flower bud
- Spring mowing with subsequent
chlorsulfuron or imazapyr application at flower bud
- Glyphosate alone at flower bud
when populations are not dense
- Spring mowing followed by glyphosate
at bud stage in wetland areas
Chemical
Foliar application
Only
foliar application methods have been shown to be effective. A list of herbicides,
sites where the compound has been approved for use, restrictions, and effectiveness
is included in the table. For rates and other important information, see
the herbicide label.
Herbicide |
Site |
Restrictions |
Effectiveness |
Telar®
(chlorsulfuron) |
Noncrop
Industrial |
Selective herbicide
(will not harm most grasses), do not apply near water. |
Excellent control
for 1-2 years |
Habitat® (imazapyr)
Stalker®® (imazapyr)
|
Riparian, Wetlands
Wildlands |
Nonselective herbicide,
do not apply near water. |
Excellent control
for 1-2 years. Treated areas typically remain void of any vegetation
for 1-2 years after treatment. |
Roundup® and
others
(glyphosate)
Rodeo®, Aquamaster® and
others
(glyphosate)
|
Wildlands
Aquatic
|
Nonselective herbicide.
Rodeo® for areas near/in aquatic sites. |
Effective unless
infestation is dense. If dense, mow area and apply to resprouting plants. |
Weedar 64®
(2,4-D) |
Wildlands
Aquatic |
Selective herbicide
(will not harm grasses) |
Somewhat effective
unless infestation is dense. If dense, mow area and apply to resprouting
plants. |
Manual and Mechanical
Mechanical
control options are typically not effective. Very small patches can be controlled
by hand removal if the process is repeated often for several years and plants
are not allowed to mature. Because root systems are brittle and can extend
so deep in the soil most mechanical techniques, such as disking, can spread
the weed and increase the density.
USE
PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY,
FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED
PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT
OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS
OR RECOMMENDATIONS.
NOTICE:
MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT
OF ANY MATERIAL.
CONTACTS
For more information on identification
and control of Perennial Pepperweed, contact:
- Debra A. Boelk, University of
CA-Davis, Plant Sciences, daboelk at ucdavis.edu
- Joe DiTomaso, University of California-Davis,
ditomaso at vegmail.ucdavis.edu
- Mark Renz, New Mexico State University,
markrenz at nmsu.edu
- University of California- Davis,
Agriculture and Natural Resources, Weed Research and Information Center,
http://wric.ucdavis.edu/
- USDA Agricultural Research Service,
Exotic and Invasive Weeds Research
http://www.ars.usda.gov/main/site_main.htm?modecode=53-25-43-00
OTHER LINKS
AUTHOR
Debra A. Boelk, University of California-Davis, Plant Sciences, Davis, CA
REVIEWER
Joe DiTomaso, Cooperative Extension Specialist, University of California-Davis,
Davis, CA
EDITOR
Jil M. Swearingen, National Park Service, Center for Urban Ecology, Washington
DC
PHOTOGRAPHS
Joe DiTomaso, Cooperative Extension Specialist, University of California-Davis,
Davis, CA
REFERENCES
Boelk, D.A., DiTomaso, J.M. and Wilson, R.G. Integrated Management of Perennial
Pepperweed. Manuscript in preparation. 2005.
Renz, M.J. Element Stewardship Abstract
for Lepidium latifolium. TNC library 04 Apr 2000. 21 Mar 2005. http://conserveonline.org/2001/05/d/en/lepilat.rtf
Swearingen, J. 2005. WeedUS: Database
of Plants Invading Natural Areas in the U.S. http://www.nps.gov/plants/alien/factmain.htm#pllists.
U.S. Department of Agriculture.
2005. USDA Plants Database. http://plants.usda.gov/
Whitson, T. "Weeds of the West" Western
Society of Weed Science.
Young, J.A., Palmquist, D.E. and
Wotring, S.O. 1997. The Invasive Nature of Lepidium latifoloium: A
Review. pp. 59-65. In, Plant Invasions: Studies from North America and Europe.
J.H. Brock, M. Wade, P. Pysek, and D. Green, eds. Backhyus Publishers, Leiden,
The Netherlands.
Young, J.A., Turner, C.E. and James,
L.F. Perennial Pepperweed. Rangelands, 17(4), August 1995.
Plant Conservation
Alliance, Alien Plant Working Group.
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