FAQ

Manitoba Purple Loosestrife Project's Top 10 FAQ

1. What does Purple Loosestrife look like?
2. Is my garden variety (cultivar) of Purple Loosestrife safe?
3. How does Purple Loosestrife escape from my garden?
4. What's so bad about Purple Loosestrife?
5. I've had Lythrum in my garden for 25 years and it hasn't spread to other locations in my yard or to my neighbor's yard. Why should I get rid of it now?
6. Are all Loosestrife varieties harmful to the environment?
7. How can I get rid of my Purple Loosestrife?
8. What types of plants can I use to replace purple loosestrife
9. How can insects help control Purple Loosestrife?
10. Where did Purple Loosestrife Come From?


 

1. What does Purple Loosestrife look like?

 

One of the most easily recognizable features of purple loosestrife, at any time of the year, is its ridged, square stem. A single plant can produce as many as 30 stems growing from a central, woody root mass. The leaves are smooth, opposite, and attached directly to the stem. Each plant can grow as tall as two metres. Loosestrife flowers in late June to late September. The flowers are pink-purple in color and are tightly clustered on a long spike. Don't confuse purple loosestrife (on right) with look-a-likes such as fireweed with its round stem (on left).

 

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2. Is my garden variety (cultivar) of Purple Loosestrife safe?

 

No. Originally many garden varieties of purple loosestrife such as Morden Pink, Morden Gleam or Dropmore Purple were considered to be sterile (did not produce seed), safe horticultural cultivars. Recent scientific studies have shown that these varieties are indeed capable of pollen and seed production. These plants can readily cross pollinate with other garden varieties, as well as wild loosestrife populations. In a Manitoba study, Morden Pink cultivars were planted near a wetland with purple loosestrife and six months later all Morden Pink plants produced viable seed. The majority of wild infestations of purple loosestrife are the result of garden escapes.

 

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3. How does Purple Loosestrife escape from my garden?

 

Each purple loosestrife plant is capable of producing an enormous number of seeds, up to three million every year. The seeds are small, light and are easily dispersed by the wind, which carries them great distances. In addition, loosestrife seeds have high viability, almost 100 per cent germination rate and remain viable after many years in the soil or submerged under water. Purple loosestrife can also spread vegetatively, by pieces of the stems or roots. Garden varieties of loosestrife can also exchange pollen with other loosestrife cultivars and wild populations. Flowers are commonly pollinated by bees, which encourage pollen flow between gardens and wild populations. Garden seeds can be transported by animals, by humans on clothing or by vehicles, and rainfall carries them into river systems and wetlands through storm water run-off.

 

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4. What's so bad about Purple Loosestrife?

 

The nicknames for purple loosestrife - beautiful killer, marsh monster and exotic invader - are telling. An invasive, weedy species, loosestrife readily establishes in a variety of urban and rural wetland habitats. Once it's present, it has a tendency to dominate, outcompeting native vegetation. The result is solid (monotypic) stands of purple loosestrife. This drastic change in species composition and decrease in biodiversity has been reported to affect the nutrient cycling regime of wetlands and the sue of the area by wildlife.

 

The displacement of native vegetation by purple loosestrife has many far reaching ecological implications, many of which still remain unknown. In urban areas loosestrife commonly takes hold in ditches and can block or disrupt water flow. In agricultural regions it can clog irrigation canals and reduces the value of forage. Once established, it is extremely difficult to eradicate. No herbicides are currently approved to control loosestrife growing in or near waterways. Small outbreaks can be removed by hand digging, but for large scale infestations this is too costly and time consuming. Since purple loosestrife can regenerate from even the smallest piece of root tissue left in the soil, digging is not a viable long term solution.

 

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5. I've had Lythrum in my garden for 25 years and it hasn't spread to other locations in my yard or to my neighbor's yard. Why should I get rid of it now?

 

For many years garden loosestrife cultivars were considered to be sterile and safe for garden use. Studies have now shown this to be false. Unfortunately, purple loosestrife was very popular among horticulturalists, who enjoy the beauty of this hardy perennial. Many gardeners still believe that their loosestrife is sterile, especially since the damage that it causes may not be noticeable in the immediate vicinity of the home. There are several benefits to removing garden varieties of loosestrife.

 

First, a potential source of pollen exchange is removed from the environment which can decrease the number of plants that become fertilized and set seed, preventing existing plants from spreading to new areas. Most loosestrife infestations originate from garden cultivars. Removing all loosestrife plants can prevent future outbreaks, as well as reducing the potential for cross-fertilization. In addition, purple loosestrife is considered a noxious weed in several provinces and states, including Manitoba. Therefore, it is illegal to sell or possess any lythrum cultivar. If a complaint is registered regarding loosestrife on your property, the plants can be removed at the owner's expense by local weed control authorities.

 

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6. Are all loosestrife varieties harmful to the environment?

All varieties of purple loosestrife are harmful to the environment. This includes wild purple loosestrife (Lythrum salicaria) and garden cultivars such as Morden Pink, Morden Gleam and Dropmore Purple. Fringed loosestrife (Lysimachia ciliata) and tufted loosestrife (Lysimachia thyrsiflora) are not lythrum species and are non-invasive.  Winged loosestrife (Lythrum alatum) is a plant native to eastern North America and is also non-invasive.

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7. How can I get rid of my Purple Loosestrife?
The best way to remove purple loosestrife from your yard is by hand digging. Make sure that all pieces of root tissue are removed and dry out the plant material thoroughly before disposal. Place all purple loosestrife plant material in a dark-colored garbage bag and ensure that the bag is tightly secured to prevent it from spreading in the landfill area. Wherever permitted, plant material should be burned. For large scale infestations and when digging is not feasible, removing the flower head is an easy alternative. Cut off the top of the plant in midsummer before the flowers set seed. Monitor the dig site for a couple of seasons to ensure no new plants are growing and, if needed, remove promptly.

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8. What types of plants can I use to replace purple loosestrife?

See this list of alternative plants.

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9. How can insects help control Purple Loosestrife?

When purple loosestrife was introduced into Canada, it escaped its natural enemies that control its spread in its European range. Biological control reunites a target weed such as purple loosestrife with its natural enemies. There are four insects approved for release against Purple Loosestrife in Canada - two leaf eating beetles called Galerucella calmariensis and Galerucella pusilla, a root mining weevil Hylobius transversovittatus and the seed weevil Nanophyes marmoratus. These specialized plant eating insects do not eat any other plants or harm our natural environment. In many areas of North America, beetles are providing almost total control of purple loosestrife. Prior to biological control there was no effective method of controlling purple loosestrife. This also means that herbicides and chemicals do not have to be used in sensitive areas like wetlands.

Marsh in 1994 before introduction of beetles. Same marsh in 1998 showing effects of beetles on Purple Loosestrife.

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10. Where did Purple Loosestrife Come From?
Purple loosestrife is an invasive perennial weed that was introduced into North America in the early 1800s. It is believed that it was introduced as a contaminant in European ship ballast and as a medicinal herb for treating diarrhea, dysentery, bleeding and ulcers. By the '30s, purple loosestrife was well established along the east coast and spread inland with the construction of waterways, drainage systems, canals, railways and highways. The first published report of purple loosestrife in Manitoba came from the Neepawa area in 1896. The next reported collection of purple loosestrife was near Lockport in 1944 and then in Winnipeg seven years later. Purple loosestrife can now be found in all major watersheds in southern Manitoba with large infestations in the Netley-Libau Marsh.

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Over the years the Manitoba Purple Loosestrife Project has gratefully received funding from the following organizations:

Ducks Unlimited

City of Winnipeg

Naturalist Services Branch

Water and Waste Department

Province of Manitoba

Manitoba Conservation

Urban Green Team

Sustainable Development Innovations Fund

Government of Canada

          Environment Canada

          Young Canada Works

          HRSDC – Canada Summer Jobs

Murphy Foundation

Manitoba Hydro



Manitoba Conservation Ducks Unlimited City of Winnipeg Invasive Species Council of Manitoba