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Blooming purple loosestrife (Lythrum salicaria) growing at a garden

Alias (scientific name in latin):Lythrum salicaria

Home Land (Origination): Europe & Asia

Arrival Date: 1800s brought to North America by settlers for flower gardens. Seeds were also present in ballasts of ships where soil was used to weigh down the vessels for stability on the ocean.

How to Identify:

  • Flowers: Individual flowers have five or six pink-purple petals surrounding small, yellow centers. Each flower spike is made up of many individual flowers. There may be from 1-50 spikes per plant.
  • Seed: Each mature plant can produce up to 2.7 million seeds each year. Seed capsules appear on the lower part of the stalk while flowers at the top are still blooming. This can be as early as July. Like tiny grains of sand, seeds are easily spread by water, wind, wildlife, and people. Germination can occur the following season, but seeds may lay dormant for several years before sprouting.
  • Leaves: Leaves are long and smooth edged. They are arranged opposite each other on the stalk in pairs at 90 degree angles. You may see them in groups of three.
  • Stalk: Stalks are 4-6 sided with larger stems up to 6 feet tall and partially woody.

Disguise (don't be fooled by look-alikes): Looks like swamp loosestrife, fireweed, blue vervain, winged loosestrife, blazing star, and gayfeather, but these are harmless. Look at a field guide to tell them apart.

(Look out for alien helpers): Watch it! Some garden centers and seed mixes have purple loosestrife in them, check the label for this sneaky alien. Garden varieties of loosestrife have also been proven to pollinate with purple loosestrife and help it multiply. You can help, don't plant garden varietites of these alien helpers.

Evidence: Purple stalks blooming in wetlands from June through early August. When purple loosestrife gets a foothold, the habitat where fish and wildlife feed, seek shelter, reproduce and rear young, quickly becomes choked under a sea of purple flowers. Some wildlife will eventually leave to find better habitat but the native plants and insects that can't move are killed by this invasion. An estimated 40,000 acres of wetlands, marshes, pastures and wet meadows in Wisconsin are affected, with an economic impact of millions of dollars.

Invaded Territory: All across Canada and the United States

Extermination Techniques: Traditional control methods, such as cutting, pulling, flooding and treating with herbicides can be time consuming. Nature itself can help! Biological controls (other plants or animals that feed on the plant) can help as long as they don't become "pests" themselves. A good solution is an insect that only craves eating the purple loosestrife. Several species of insects have been studied by the Wisconsin Department of Natural Resources at controlled release sites. The Galerucella beetles will eat the leaves quickly and can keep the plant from flowering. Unfortunately Galerucella doesn't spread to new sites quickly, but people have been starting new colonies and moving them to infested areas. Some citizen groups have already jumped in and helped raise the beetles in a nursery, released and monitored them on the landscape. This is a great community or class project. DNR researchers can supply you with directions and the technical know-how to raise and release the beeetles. Call 608-266-2554 or send an email to Brock Woods, Research Ecologist at the DNR at

Help Stop the Alien Invasion!

You can help teach people about these invaders, contact: nurseries that grow flowering plants, community garden groups, conservation groups, the agricultural community, and your next door neighbor. The best time to control purple loosestrife is June through August when it's in flower and before it goes to seed. Purple loosestrife can be controlled by these methods:

  1. Digging & Hand Pulling - Pull plants when they are young or in sand. Older plants have tough roots, but a garden fork will help. Remove as much of the root system as possible, broken roots may sprout new plants.
  2. Biological Control - In areas of severe infestation, this method can work best. Biological control is managed by the WDNR and you can help rear insects and release them.
  3. Cutting - First, remove flowing spikes to prevent this year's seeds from producing more aliens. Then, remove last year's dry seed heads. Put seed heads in plastic bags, so seeds can't spread. Finally, cut the stems at the ground to prevent growth.
  4. Chemical Control - Used only by adults in a dry, upland area, and on private property where plants can be hand sprayed.

Contact the Purple Loosestrife Biocontrol Project, DNR Science Operations Center, 2801 Progress Rd, Madison, WI 53716, 608-266-2554.