There are many alternative garden perennials that can be planted in place of the purple loosestrife. Removing purple loosestrife from wetland areas is not easy. Herbicides cannot be used in many of the areas where purple loosestrife is found. In areas with large infestations, digging up the plant is labour intensive, can disturb the soil, and increases the chance of spreading seeds.
In Manitoba, biological control has been used to help control the spread of purple loosestrife. Research has found that all varieties of lythrum produce seed, which is a source of infestation to aquatic sites, including rivers, lakes, sloughs, dams, dugouts, bogs, swamps, irrigation ditches, streams perennial or semi-permanent and other water courses, or wet sites. To prevent spread into aquatic sites, all purple loosestrife plantings are required by state law to be removed.
Purple loosestrife is a rhizomatous perennial forb introduced to North America from Eurasia and Africa. Wild infestations are associated with moist or marshy sites. The stems are erect 1. Leaves are simple 0. The most identifiable characteristic of purple loosestrife is the striking rose to purple colored flowers Figure 4.
The flowers are arranged on a spike, which can be a few inches to 3 feet long. Each flower has five to seven petals arising from a cylindrical green tube. The plant usually flowers from early July to mid-September in North Dakota. The seed capsule is two celled and contains many very small seeds 1 mm long or less. The roots become thick and woody in mature plants.
The aerial shoots die in the fall and new shoots arise the following spring from buds at the top of the root crown. Although the root crown expands and produces more shoots each year, the maximum growth of the root crown diameter is limited to about 20 inches.
Figure 4. Purple loosestrife flowers are very striking purple arranged on a spike. Spread of purple loosestrife is primarily by seed, but the plant can also spread vegetatively from stem cuttings. Research at NDSU has shown that seed viability of purple loosestrife growing in North Dakota wetlands ranged from 50 to percent.
With approximately 2. Several methods are available for purple loosestrife control, including mechanical, biological, and chemical. The size and location of a specific infestation will determine the best control methods. In general, small infestations of a few plants can be controlled by digging, especially when plants are only a few years old. Small infestations can be controlled by removing all roots and underground stems.
It is difficult to remove all of the roots in a single digging, so monitor the area for several growing seasons to ensure that purple loosestrife has not regrown from roots or seed. This method is most useful on garden plantings or young infestations. Dispose of plants and roots by drying and burning or by composting in an enclosed area. Take care to prevent further seed spread from clothing or equipment during the removal process. Removal of all plant material is important.
Small segments of purple loosestrife stems can become rooted and reestablish the infestation. Herbicides can be used to control purple loosestrife in areas too large to be controlled by digging. Also, herbicides can be applied to individual plants selectively in landscape situations to prevent killing desirable plants.
Infestations growing along streams or in marshy areas may require specialized equipment and application by trained professionals. Glyphosate will provide good control of purple loosestrife when applied from July to early September. Many formulations of glyphosate are sold but only those labeled for aquatic use can be applied in or near water. For example, the Rodeo and Glypro formulations of glyphosate can be used in water. Pull plants before they flower if possible to avoid scattering seeds in the removal process.
Remove all stems from the wetland area as discarded stems will sprout and create new plants. Clusters in excess of plants, up to 3 acres, and plants too large to pull out, are best controlled by herbicides. Currently, loosestrife can be controlled with Roundup on terrestrial sites and Rodeo in wetlands and over water.
These are U. Environmental Protection Agency registered herbicides that should be applied by licensed herbicide applicators following label instructions. Effective control of large infestations is dependent on future research. Present action is aimed at containing the spread of this weed.
The tiny seeds are easily spread by water, wind, wildlife and humans. In , the Canadian and American governments approved the release of two European leaf-eating beetles, Galerucella calmariensis and G. The beetles are natural enemies of purple loosestrife and feed primarily on the plant, although they occasionally eat other species of loosestrife.
This biological control of purple loosestrife can reduce populations by up to 90 per cent and allow native plants to re-establish. The beetles were widely released in Ontario, and purple loosestrife populations at many of these sites have been significantly reduced.
Purple loosestrife was first introduced to the Atlantic coast of North America. From there, it spread westward across the continent to all Canadian provinces and all American states except Florida, Alaska and Hawaii.
In Ontario, the plant has spread widely throughout the Great Lakes-St. Similar species that may be mistaken for purple loosestrife include fireweed Epilobium agustifolium , blue vervain Verbena hastata , blazing stars Liatris spp. Please contact the Invading Species Hotline at To have a better experience, you need to: Go to your browser's settings Enable JavaScript.
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