Description

Purple loosestrife is an herbaceous wetland perenniala plant whose growth dies down annually but whose roots or other underground parts survive that can grow 1.5-5 feet tall. The leaves are either opposite or in whorls of three. They can be pubescentsoft down or fine short hairs on the leaves and stems of plants or glabroussmooth; free from hairs. They are lanceolateshaped like the head of a lance; of a narrow oval shape tapering to a point at each end to linear in shape and 1-4 inches long. The larger leaves can be cordate or clasping at their bases. The flowers are purple, magenta or pink. They are numerous and borne on spikes that are between 4-16 inches long. The hypanthium is linear and twice as long as the sepals. Each flower has 5-7 petals, and the open flowers measure 0.3-0.5 inches in diameter. The flowers are in bloom from July to September. The fruits are capsules, each containing numerous reddish-brown seeds.

Habitat

Purple loosestrife is most often found in situations where the soil is moist. However, it prefers areas with shallow water, and does not grow as prolifically in deep-water situations.

Purple loosestrife is a plant of freshwater wetlands, including marshes, wet meadows, fens, bogs, openings in forested swamps, intermittent streams and pools, pond and lake shores, stream banks, and ditches. It is also common in fresh and brackish tidal wetlands. Loosestrife can establish on recently disturbed upland soils, although it remains smaller there than in wetlands. In recently-disturbed wetlands such as drawn-down ponds and abandoned beaver ponds and pastures, loosestrife may be highly dominant.

History and Introduction

The first report of Lythrum salicaria in North America was in 1814. Before the year 1900, 14 of 30 populations of this plant were located in estuaries from Massachusetts to New Jersey. The location of these sites would indicate that the plant was introduced somewhere in this area. There are several hypotheses on how this plant was originally introduced. It could have been a part of ship ballast from Europe, or attached to sheep. Lythrum salicaria was also planted as a source of nectar for beekeeping, as an ornamental, and for medicinal reasons. By the 1900's there were more inland populations being reported, one of these being in New Hampshire. Since these initial introductions it has spread by being planted in gardens and by waterways.

Threats

Purple loosestrife has the ability to completely dominate wetlands, forming a vast, monotypic standsan area dominated by a single species. These stands prevent the establishment of native wetland plants. It can also have an effect on native wildlife that may not be able to use the plants as effectively for food or cover. By forming these dense stands, Lythrum salicaria can clog waterways, causing problems for both commercial and recreational uses of these areas. Lythrum salicaria can produce up to 2.5 million seeds per plant. These seeds persist in the seed bank for years, even if the plants themselves are eradicated from an area.

Dispersal Methods

Lythrum salicaria reproduces through prolific seed dispersal. The seeds usually fall to the ground after they have ripened. They can be moved longer distances by water or by becoming attached to waterfowl.

Purple loosestrife enjoys an extended flowering season, generally from June to September, which allows it to produce vast quantities of seed. The flowers require pollination by insects, for which it supplies an abundant source of nectar. A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million, minute seeds per year. 

Purple loosestrife also readily reproduces vegetatively through underground stems at a rate of about one foot per year. Many new stems may emerge vegetatively from a single rootstock of the previous year. 

Control

Mechanical

Small infestations of young purple loosestrife plants may be pulled by hand, preferably before seed set. Older plants can be removed with a shovel. Landfill or burn removed plants. 

Chemical

It can be effectively controlled using any of several readily available general use herbicides such as glyphosatea widely used herbicide that can kill certain weeds and grasses, it works by blocking an enzyme essential for plant growth or triclopyrherbicide used to control both broadleaf and woody plants. These herbicides may be most effective when applied late in the season when plants are preparing for dormancy. However, it may be best to do a midsummer and a late season treatment, to reduce the amount of seed produced. Follow label and state requirements.