This pretty plant is known to those threatened by its invasion as the 'purple peril'.

The pretty magenta flower spikes of purple loosestrife produce seeds by the millions, and when carried by wind or water, enable the plant to escape from gardens and establish populations in natural areas. Once in a wetland, purple loosestrife easily replaces native vegetation and degrades habitat for ducks, turtles and other wildlife. Park staff have been actively managing purple loosestrife since 1988. A group of exotic plant experts gathered at the park to review the program after ten years of implementation. They concluded that the purple loosestrife management program at Acadia is one of only a few examples of successful exotic species control (Hiebert et al. 1997). The success is due to the use of several strategies and control techniques. These are integrated into an overall plan for holding back the potential invasion of what some call the purple peril.

Acadia's Integrated Pest Management (IPM) Strategy for purple loosestrife is outlined below:

1. Prevention. Loosestrife seeds germinate in moist, exposed soil and do especially well in disturbed areas. Water drawdown is avoided during the growing season which exposes mudflats where seeds can germinate. Disturbance by construction equipment is kept to a minimum and disturbed sites are closely monitored.
     
2. Early Detection. All park wetlands are surveyed at least every three years to pinpoint locations of new infestations which are easier to control when small. High risk areas, i.e. those near disturbance such culverts or beaver lodges are surveyed annually.
     
3. Chemical Control. Rodeo (glyphosate) herbicide is spot-applied in all infested areas. Backpack sprayers with hand-held nozzles are used to carefully spray all individual purple loosestrife plants found. Flowering heads are removed and burned, so no seeds can disperse into the area.
     
4. Biological Control. Populations of purple loosestrife outside the park continually threaten park wetlands when their seeds blow on the wind or float down streams into the park. Insects native in the plants indigenous range in Europe have been shown to feed on loosestrife plants and therefore keep purple loosestrife populations from spreading rapidly (Batra et al. 1986). These natural predators have been introduced into the United States and Canada as biological controls which feed on the roots and leaves of loosestrife plants and reduce the plants overall vigor (Malecki et al. 1993; Blossey l994; light et al. 1995). Two beetles, Galerucella sp., were released in a loosestrife population outside the park in 1997. Biologists hope the beneficial insects will develop self-perpetuating populations and provide continued control of loosestrife with no annual costs. The insects may naturally spread into the park, reducing the need for herbicide applications.
     
5. Evaluation. In 1989, seven permanent sampling grids consisting of five parallel transect lines 5 meters apart were established in several watersheds containing purple loosestrife. These grids are surveyed annually to track the abundance of purple loosestrife populations. This quantitative data has helped measure the success of control techniques. Since 1989, the number of purple loosestrife plants in the grids have declined overall. Quantitative sampling grids were also established at the biological control site outside the park to evaluate the success of this control technique.
     
6. Education. The most important part of the IPM plan is getting the word out about how purple loosestrife threatens wetlands. Acadia uses information displays, newspaper articles, television programs, and school and public presentations to help the public understand the threat purple loosestrife poses to wetlands. Public support is essential for effective purple loosestrife control both inside and outside the park.
     

Without the efforts described above, many of Acadia's wetlands would have been overrun by purple loosestrife years ago. Wildlife habitat would have been degraded and much of the wetlands natural diversity would have been lost. Today, purple loosestrife is an uncommon plant in the park, and native vegetation is thriving in Acadia's wetlands. This effective, integrated approach will continue to be used to protect Acadia National Park from this invasive pest.

For more information contact: Linda Gregory, Acadia National Park, P0 Box 177, Bar Harbor, ME 04609; OR email: lindagregory@nps.gov

Literature Cited:

Batra, S.W.T., D. Schroeder, P.E. Boldt and W. Mendl. 1986. Insects associated with purple loosestrife (Lythrum salicaria L.) in Europe. Proceedings of the Entomological Society of Washington 88(4): 748-759.

Blossey, B. 1995. Impact of Galerucella pusilla and G. calmariensis (Coleoptera: Chrysomelidae) on field populations of purple loosestrife (Lythrum salicaria). Proceedings of the Eighth International Symposium on biological Control of Weeds, 2-7 February 1992, Lincoln University, Canterbury, New Zealand. Delfosse, E.S. and R.R. Scott (eds.) DSIR/CSIRO, Melbourne, pp. 27-31.

Hiebert, R., A. Gibbs, T. McLendon, N. Pavlovic, J. Randall, J. Taylor. and S. Walasewicz. 1997. Purple loosestrife management program review; Acadia National Park, Maine: August 6-9, 1996. Edited by J.H. Connery. U.S. Department of the Interior, National Park Service, Natural Resources Technical Report NPS/NESO-RNR/NRTR/97-02. Boston, MA. 43 pp.

Hight, S. D., B. Blossey, J. Laing and R. Declerck-Floate. 1995. Establishment of insect biological control agents from Europe against Lythrum salicaria in North America. Environmental Entomology 24(4): 967-977.

Malecki, R.A., B. Blossey, S.D. Hight, D. Schroeder, L.K. Kok, and J.R. Coulsen. 1993. Biological control of purple loosestrife. Bioscience 43(10): 680-686.