Invasive Plant Species Control
Purple Loosestrife
(Lythrum salicaria)
Native Substitutes
- Swamp milkweed (Asclepias incarnata)
- Fireweed (Epilobium angustifolium)
- Spotted Joe-Pye-weed (Eupatorium maculatum)
- Swamp smartweed (Polygonum coccineum)
Description
Appearance: Perennial forb, 3-7' tall with multiple (30-50) four, five, or six-sided stems arising from a single rootstock.
Leaves: Opposite or alternating in 90 degree angles; sometimes appearing in groups of three; lance-shaped, downy with smooth edges; stalkless.
Flower: Magenta flower spikes bloom all summer. Individual flowers have 5 or 6 petals.
Seeds: Tiny; about 2.7 million per plant annually. Seeds remain viable in the soil for many years.
Root: Large, woody taproot with extending fibrous rhizomes forming a dense mat.
Ecological Threat
Purple loosestrife invades many wetland types including wet meadows, stream banks, pond or lake edges and ditches. Its ability to also reproduce vegetatively allows it to expand quickly and form monotypic stands that choke out native plants. Purple loosestrife was introduced from Europe as a garden perennial.Legal status: Regulations forbid the sale of Purple loosestrife in 24 states. This plant and any hybrids, cultivars, or varieties are prohibited exotic species in Minnesota and may not be possessed, imported, purchased, sold, propagated, transported, or introduced except by permits allowed by state law.
Control Methods
| Mechanical | Chemical | Biological |
|---|---|---|
| Pulling and digging small infestations of young plants, or before seed ripens when growing in sandy soil. For larger plants use a garden fork | Spot spraying with glyphosate (Rodeo for wetlands). Most effective in fall when plant is preparing for dormancy | Two leaf-eating beetles, Galerucella spp., are available for control of purple loosestrife. The beetles have been very effective at reducing loosestrife infestations at many locations nationwide |
| Cutting at ground level at blooming time |
Sources
Purple Loosestrife: what you should know, what you can do (brochure). 2001. Ontario Federation of Anglers and Hunters.
Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants, 1997 Plant Conservation Alliance: Alien Plant Working Group www.nps.gov/plants/alien/fact The Nature Conservancy Element Stewardship Abstract
Minnesota Department of Natural Resources, Restore Your Shore CD, 2001
