Purple Loosestrife

Where did purple loosestrife come from?

Purple loosestrife is native to Great Britain, central and southern Europe, central Russia, Japan, Manchuria, China, southeast Asia and northern India.

The plant was first introduced to northeastern United States and Canada in the 1800s for its medicinal, decorative and horticultural values. It could have also been introduced through various seed sources such as: ship ballast, livestock feed and bedding. Soon after its entry, purple loosestrife was entrenched in the northeastern area and spreading.

Invasive Species, Purple Loosestrife, Montezuma NWR, NY, FWS
Invasive Species, Purple Loosestrife, Montezuma NWR, NY, FWS

Where and How It Spreads

Purple loosestrife is perhaps the most prevalent invasive species in the U.S., covering about 400,000 acres of federal land, including wetlands, marshes, pastures and riparian meadows.

Although the purple loosestrife is most common and abundant in the northeastern United States and Canada, the plant has spread across North America. According to the U.S. Fish and Wildlife Service, it is in every state except Florida.

The construction of roads and their ditches promoted the spread of Purple Loosestrife. These ditches supply long stretches of favorable habitat for the plant to thrive and are pathways for the plant to spread from exposed to unexposed wetland habitats.

Roadside mowing has also assisted the spread of seeds and stem parts mechanically. The plant is commonly planted in perennial gardens and used in wildflower seed mixes because of its mid-summer magenta blossoms. And, large tracts of unused farmland tend to supply ample moisture allowing purple loosestrife to proliferate to an extent that it has created near monocultures inhabiting vast areas of old pastures and meadows.

Purple loosestrife continues to be sold to gardeners, except in Minnesota, Wisconsin, and Illinois, where buying and selling it violates state regulations.

Ecological Impacts

Purple loosestrife invades various wetlands, such as: freshwater wet meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs and ditches.

It crowds out at least 44 kinds of native grasses, sedges and other flowering plants that offer higher-quality nutrition for wildlife. The plant confines native wetland plant species including some federally endangered orchids and swamp rose mallow, and it reduces habitat for waterfowl. Some declining species directly affected by its invasion are the bog turtle, black tern and canvasback duck.

Economic Impacts

The continuously expanding purple loosestrife acreage requires an annual cost of control upwards of $45 million for habitat restoration and control methods. In addition to the ecological damage it causes, purple loosestrife also affects farmlands by clogging irrigation and drainage ditches and causing the degradation and loss of forage in lowland pastures.

Control and Removal

Mechanical, biological and chemical removal options exist. The size and location of the invasion determine the control methods. Typically, digging manages small invasions of a few plants, especially when they are only a few years old. Larger infestations require herbicidal and/or biological control agents.

Eliminating all the roots and underground stems of the plant by digging is mechanical removal, which is most effective with small, young invasions. After the initial digging, the area should be monitored over several seasons to ensure the plant’s eradication. Drying and burning or composting in an enclosed area will dispose of the plants efficiently. Caution should be taken during every step of the process because small pieces of stem can root and reestablish the invasion. This also means, be careful of clothing worn and equipment used during the removal process.

Herbicides chemically control purple loosestrife in areas too large to manage by digging. They can be applied to individual plants so as not to harm desirable plants nearby. Specialized equipment and treatment by professionals might be needed for removal along streams or in marshy areas. Some effective herbicides are Glyphosate and Garlon (triclopyr).

Biological control is considered the most effective control method for large invasions and long-term treatment. Galerucella pusilla and Galerucella calmariensis are two bio-control insect species that have been the most successful in the treatment of purple loosestrife. The adult and larvae of these leaf-feeding beetles eat the purple loosestrife leaves and flowers and have greatly reduced invasions over several seasons.

Physical Description

Purple loosestrife is an erect, perennial herb that grows from 0.5 to 3 meters tall depending on habitat conditions. It has a square, wooded stem and opposite or whorled leaves that are mainly lance-shaped and stalkless. At the base of the plant the leaves are heart-shaped or rounded. The length of the leaves varies from 3 to 10 cm. Leaves at the base and inside of flower spikes tend to be smaller and attached alternately.

The upper section of the purple loosestrife is generally covered with short hairs. Several specie varieties have been distinguished on the basis of different hair distribution and thickness on the stem and leaves and different leaf shape.

In the summer the plants produce lush magenta-colored flowers. They are practically stalkless, 5 to 7 petal flowers. Mature plants can have 30 to 50 stems coming from a single rootstock.

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