Purple Loosestrife, a "Poster Child" for Invasive Plants

Purple Loosestrife, an invasive species found in most if not all 50 States could easily be the poster child for invasive plant species. It represents them well in terms of costly impacts, spread strategies, and life history that allow it and other invasives to cause economic and ecologic impacts across the nation.

Although spreading still, this flamboyant nonnative appears on seven State noxious weed lists. Why is that? First of all, 11 States have no noxious weed list at all. Secondly, the bloom is so striking, often the political will does not exist to add it to a State's weed list. Thirdly, many State agencies, wildlife organizations, and commercial nurseries do not yet think the plant is a problem and continue its use.

Background:
Let's set the record straight! Purple loosestrife, Lythrum salicaria and its cultivars, IS a pest plant. Five years ago, the plant made The Nature Conservancy's "Dirty Dozen" list. The list included six invasive animal species and six plant species. Purple loosestrife joined the list with aggressive invaders like tamarisk, leafy spurge, hydrilla, miconia, and Chinese tallow. Twenty years ago, the U.S. Fish and Wildlife Service published a one page, "Purple Loosestrife Alert". But the plant had been well established on the Eastern seaboard 150 years before. Since then it has been called the "purple plague", "biological pollution", "a beautiful killer", "deadly threat" and more. In 1996, the Brooklyn Botanic Garden included purple loosestrife in its list of troublesome landscape plants, Invasive Plants, Weeds of the Global Garden.

Fig. 1. Structure, growth forms, and gield indenification characters of Lythrum salicaria (purple loosestrife)

Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands, 1987

Accidental Introduction:
Purple loosestrife is a typical invasive plant in that its origin is in another country and once established here, expanded its populations easily with no competition to keep it in check. How did it arrive here in the first place? The records of its arrival are not clear; but seed first came in ship ballasts and as a garden herb. Later horticulturists introduced it to gardens. Other vectors noted in the literature include: sheep and raw wool brought from Europe. Well established by the 1830's throughout Eastern North America, loosestrife was spread by the building of canals, the grazing of wetland meadows, marine commerce, the disturbance of watersheds by agriculture, agriculture seed from Europe and hay for livestock. Within watersheds, migratory waterfowl, watercraft, and small mammals likely spread the seed as well.

Intentional Introduction:
Although most of the reasons for the early spread of this invasive plant resulted from nonintentional introductions, some introductions were purposeful. The plant was introduced into herb gardens for its medicinal properties. Loosestrife was also introduced into the garden trade as "a plant of great beauty". Purple loosestrife has many desirable garden characteristics: tolerated shade and a range of soils and moistures, had a long bloom period, easy to propagate, and was showy for many weeks. Apicultural suppliers used purple loosestrife as a honey plant. Wildlife habitat seed suppliers sold purple loosestrife as a wetland plant. Wildflower seed companies included it in their mixes. Suddenly the plant was spread on many commercial fronts, increasing accidental seeding opportunities.

Spread:
The spread of purple loosestrife throughout the country took 150 years. Herbarium records and published floras document its whereabouts and movement. However, by 1980, the USFWS suggested that one plant per acre constituted an infestation. An exaggeration? By 1980, we knew the plant

Weeds are often spread by people taking them home for flower arrangements

1. produces a minimum of 200,000 seeds per plant,
2. reproduces vegetatively from small pieces,
3. tolerates a wide range of environmental conditions,
4. remains viable under two feet of water, and
5. has no natural enemies.

One plant per acre was a biological wildfire waiting to happen! By then purple loosestrife was referred to as an exotic, an alien, a weed, a pest plant, an introduced species.

Impacts:
Economic and environmental costs are great. At first we recognized the following impacts. Today, as the case study reveals, we know of more impacts.

1. Degrade wildlife habitat, impacting hunting and fishing economy.
2. Compromise forage value of wetland hay and pasture.
3. Threatens property value of rural land.
4. Reduce biodiversity of natural areas, creating monocultures.

Plant Life History:

• perennial
• 6-10 feet tall at maturity
• herbaceous
• native of Eurasia
• prefers wetland habitats
• leaves are lance-shaped and grow opposite each other or in whorls of three
• blooms July/September
• identifiable by strong brown color of stalks in fall and winter
• creates solid monocultures
• 200,000+ seeds per plant annually
• seed viability tolerates flooding
• spreads by water, wind, birds and mammals, boats, disturbance

Case Study:
An example of spread, repeated over and over across the country, is that of the Montezuma refuge in New York. In 1965, an impoundment was created. This disturbance aided the introduction of purple loosestrife. By 1968, less than 5% of the biomass of emergent-aquatic vegetation was purple loosestrife. Ten years later, 90% of the desirable aquatics were displaced by purple loosestrife. Much was learned about the impacts of this invasive plant on wildlife habitat as a consequence. o A controlled drawdown and subsequent flooding only increased the stand.

• Muskrats require cattails that can be replaced by purple loosestrife.
• P.L. is crowding out threatened wetland plants and wildlife.
• Threatened critters include: bog turtle, black tern, and the canvasback.
• P.L. threatens wetland crops like wild rice and wild hay/mulch.
• P.L. monocultures reduce biodiversity
• P.L. reduces recreational use of a wetland

What You Can Do:

As a homeowner -
Vigilantly watch your own back yard for new invasions.

• Report new invasions to your State's Department of agriculture, DNR, or...
• Control small invasions first. Get help with large populations.
• Work with your own State's Invasive Plant Council
• Work with your local media to increase public awareness
• Host a neighborhood weed watch get together
• Avoid planting invasive ornamental plants. Chose native plant species as much as practicable and available in your region.
• Avoid plants like: English Ivy, Common Buckthorn, Norway Maple, Russian Olive, Barberry, Multiflora Rose, Autumn Olive, Oriental Bittersweet, etc.
• Join volunteer groups in removing invasive plants from parks, preserves, etc.
• On camping trips, clean boots and gear before and after

As a vegetation manager -

• Inventory the land you manage and map current infestations
• Plan how to use your resources wisely to have the greatest impact
• Consider working with schools through out the State to raise P.L. beetles
• Be an active member of your State's Invasive Plant Council or Association
• Analyze project sites before they begin, to minimize spread of invasives
• Use weed-free mulches as much as possible
• Avoid planting nonnative plants that you know to be aggressive,
• .....especially those in erosion control mixes or "wildflower" mixes.
• Avoid nonnatives like Russian Olive, reed canary grass, crownvetch, tall fescue, tamarisk, black locust, white poplar, bush honeysuckles, and so on.
• Train your crews to identify the problem plants and controls in your region
• Create a District by District reporting system of new invaders
• Use District group e-mail to distribute photo I.D. and controls for new weeds
• Establish partnerships with County, State and Federal agencies to do more
• Consider use of GIS for mapping and planning purposes
• Use an integrated vegetation management approach always.
• Know and control your own State's and adjacent State Noxious Weed Lists.
• Remember whenever you disturb soils, you invite invasive species

References:

Harper, Bonnie L.1986. A Minnesota Counterattack on Purple Loosestrife (Lythrum Salicaria). The Prairie: Past, Present and Future, Proceedings of the Ninth North American Prairie Conference. Tri-College University Center for Environmental Studies, Fargo, North Dakota.

Daniel Q. Thompson, Ronald L. Stuckey, Edith B. Thompson, 1987. Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands. United States Department of the Interior, Fish and Wildlife Service, Washington, DC. Randall, John M. and Janet Marinelli, Editors, 1996. Invasive Plants, Weeds of the Global Garden. Brooklyn Botanic Garden, NY.

Stein, Bruce A. and Stephanie R. Flack, eds. 1996. America's Least Wanted: Alien Species Invasions of U.S. Ecosystems. The Nature Conservancy, Arlington, Virginia.

Army Corps of Engineers, Noxious and Nuisance Plant Management Information System (PMIS), a CD-rom. 1996. Vicksburg, MS.

Websites:

www.invasivespecies.gov (home of the invasive species council with EO13112 info)
http://refuges.fws.gov/FICMNEWFiles/FICMNEWHomePage.html (homepage of FICMNEW and other linkages)
www.fhwa.dot.gov/roadsides (webpage for roadside vegetation management)
http://tncweeds.ucdavis.edu (link to new weed control methods manual)
www.nps.gov/plants (home of "Weeds Gone Wild", more on alien plants)
www.blm.gov/weeds (homepage of useful weed news and links)