HPIPM:Purple loosestrife

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Rosanae
Order	Myrtales
Family	Lythraceae
Genus	Lythrum

Scientific Name

Lythrum salicaria

Common Name

purple loosestrife

Purple loosestrife (Lythrum salicaria)

Author: Tim Prather, University of Idaho, Department of Plant, Soil, and Environmental Sciences

Adapted from: Idaho Weed Resource webpage on purple loosestrife.

Identification and Life Cycle

Purple loosestrife (Lythrum salicaria) is a non-native emergent aquatic weed in the loosestrife family (Lythraceae). Purple loosestrife is a hardy perennial that can grow over 8 feet tall. Cotyledons are ovate, about 0.2 inch long with petioles about half the length of the cotyledons. The stem below cotyledons often has purple dots. First sets of leaves are opposite, about 0.25 to 0.3 inch long. Stems are usually four-sided and much branched, bearing opposite or whorled, 4-inch long, lance-shaped leaves. Crowded flower spikes develop at the stem tips in midsummer. Flowers are 1 inch in diameter with six reddish purple, wrinkled petals that appear as if they have been crushed. A single plant may produce over 2.5 million tiny seeds per year.

Habitats

Purple loosestrife occurs in wetlands, along stream banks, and shorelines of shallow ponds.

Impacts

Impacts on wildlife have not been well studied; however, purple loosestrife appears to reduce waterfowl and aquatic fur bearer activity severely, and alters nutrient cycling regimes. Purple loosestrife can form dense virtually monotypic stands that can exclude desired species.

Biology and Ecology

Purple loosestrife reproduces primarily by seed, although new shoots can develop from sections of roots. Seeds require warm temperatures and moist open soils for germination. Seedlings grow rapidly and can flower in their first year. Mature plants develop sturdy laterally branching root stocks that can produce more than 30 annual shoots. Established purple loosestrife plants can tolerate a broad spectrum of growing conditions including permanent flooding, low water and nutrient levels, and low pH. Plants are long lived and seeds can remain viable in the soil for several years. Seeds float and can be carried long distances in river, canal, and ditch systems.

Management Approaches

Biological, mechanical, and chemical methods can be used to control purple loosestrife.

Biological Control

Four biological control agents are available for purple loosestrife. They include two leaf feeding beetles (Galerucella calmariensis, and G. pusilla), a flower weevil (Nanophyes marmoratus), and a root mining weevil (Hylobius transversovittatus).

Mechanical and Cultural Control

For small infestations, hand pulling can eliminate purple loosestrife. However, the plant will re-sprout if the entire root is not removed. Frequent mowing may be effective if cut stems dry rapidly.

Chemical Control

Several herbicides are available for control of purple loosestrife.

Examples of herbicides that can be used to manage purple loosestrife

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.

References

For more information and images please visit IPM Bugwood. http://www.ipmimages.org/search/action.cfm?q=purple%20loosestrife&Start=1&results=15