Purple Loosestrife

Purple loosestrife is a perennial plant, three to seven feet tall with a dense bushy growth of 1-50 stems. Showy flowers that vary from purple to magenta are positioned along the numerous long spikes and bloom in mid to late summer. Leaves are opposite, nearly linear, and attached to four-sided stems without stalks. It has a large, woody taproot with rhizomes that form a dense mat.

The plant has a wide tolerance of physical and chemical conditions and is able to reproduce prolifically by both seed and vegetatively. A single flower stalk can produce from 100,000 to 300,000 seeds per year. Seeds can germinate many years after they have entered the soil. The absence of natural predators also contributes to purple loosestrifes proliferation.

Any sunny or partly shaded wetland is susceptible to a purple loosestrife invasion. The plant's preferred habitat includes marshes, stream margins, and wet prairies. It's tolerant of moist soil and shallow water sites such as pastures and meadows, although established plants can flourish in drier conditions.

Purple loosestrife displaces native wetland vegetation and degrades wildlife habitat. Eventually, purple loosestrife can overrun and almost entirely eliminate open water habitat. The plant can also be detrimental to recreation by choking waterways.

Preventing the spread is the easiest control method and the best way to stop purple loosestrife. Monitor your wetlands regularly and remove any new young plants. Find pioneering plants or isolated small colonies, especially in areas otherwise free of loosestrife. If you remove plants, do not leave stems or cuttings that can resprout or disperse seed.

Dispose of plants and seeds in a landfill, or dry and burn them. Composting will not kill the seeds. Keep clothing and equipment seed-free to prevent its spread. Rinse all equipment used in infested areas before moving into uninfested areas, including boats, trailers, clothing, and footwear. Remove new plants wherever you see them. Follow-up is essential for all invasive species control methods.

Pulling and digging can be effective, but can also be disruptive by creating disturbed bare spots, which are good sites for invasive plant seeds to germinate. Do not to leave root fragments that can grow into new plants. Use these methods primarily with small plants in loose soils, since this does not usually leave behind large gaps or root tips. Large plants with multiple stems and brittle roots often do.

Chemical treatment is a good way to eliminate purple loosestrife quickly, especially with mature plants. Timing is important, so treat in late July or August. Make sure you treat before flowering to prevent seed set. Chemical treatments can control phragmites effectively. However, since it is most commonly found in wetland communities, Department of Natural Resources permits are required for chemical treatments, mechanical treatments, and even some manual treatments. For further information on chemical controls, visit the DNR website at www.dnr.state.wi.us/invasives/fact/loosecontrol.htm

Biocontrol is considered the best option for more control for heavy infestations. Two species of galerucella beetle, which are host specific to purple loosestrife, have been introduced in our area. . The larvae of these beetles chew on the buds, leaves and stems of the plants, preventing seed production. These insects will not eradicate loosestrife, but can significantly reduce the population and prevent further spread.

The good news is that Calumet County Master Gardeners have been engaged in this purple loosestrife biocontrol program for many years. They have been raising beetles in Calumet County and releasing them locally and in surrounding areas wherever purple loosestrife is a threat to native communities. Before using any chemical control methods on your purple loosestrife, contact the Calumet County Master Gardeners to find out if your plants have biocontrol beetles at work. For additional information on biocontrol of purple loosestrife, visit the website listed above.