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Purple loosestrife Lythrum salicaria L. |
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Purple
loosestrife is a member of the Loosestrife family. It is a
perennial introduced from Europe. The erect, square stem can
be smooth to hairy, multi-branched and 1-1/2 to 8 feet tall.
The leaves are lance shaped, entire, and are whorled. The
magenta-colored flowers, which have five to seven petals,
are arranged in long racemes. Purple loosestrife can be found in moist wetland sites throughout the state. It is a highly aggressive invader species. If left unchecked, a wetland will eventually become a monoculture of loosestrife. This plant poses a severe threat to waterfowl habitat and can impede water flow in irrigation ditches. |
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This information courtesy of the Colorado Natural Areas Program Family: Lythraceae (Loosestrife) Other Names: purple lythrum USDA Code: LYSA2 Legal Status: Colorado Noxious Weed List A Identification Lifecycle: Perennial Growth form: Forb or woody sub-shrub Flower: Flowers are purple with 5-7 petals arranged in long vertical racemes. Seeds/Fruit: Fruits are many-seeded capsules, seeds are small and ovoid. Leaves: Leaves are simple, entire, and opposite or whorled (Whitson et al. 1996). Stems: Annual stems arise from a perennial rootstock (Mal et al. 1992). Stems are erect, and often grow 6-8 feet tall. Plants become taller and bushier over the years as the rootstock matures. Roots: Short rhizomes and taproot. Seedling: No information available. Similar Species Exotics: None known. Natives: Sometimes confused with fireweed (Epilobium spp.), which have 4-petaled flowers. Impacts Agricultural: No information available. Ecological: Purple loosestrife is an ornamental species that often escapes to sites such as streambanks or shallow ponds. The invasion of purple loosestrife leads to a loss of plant diversity, which also leads to a loss of wildlife diversity (Bender and Randall 1987). Purple loosestrife germinates at such high densities that it outcompetes native seedlings. Infestations can become dense and impede water flow in canals and ditches. When placed under moisture stress, purple loosestrife may produce additional roots, which may give it a competitive advantage over other species. It is an aggressive invader of wetlands. Once it is established, it often displaces native wetland species and degrades wildlife habitat. If purple loosestrife is left unchecked, the wetland eventually becomes a monoculture of loosestrife (Bender and Randall 1987). Where purple loosestrife is competing with cattails, it is favored by fluctuating water levels because marsh drawdown aids in seedling establishment (FEIS 1998). However, where water levels remain constant and relatively deep, cattails may be able to outcompete purple loosestrife (FEIS 1998). Habitat and Distribution General requirements: Purple loosestrife usually occurs in marshes, wet meadows, stream margins, shores of lakes and wetlands. A few of its most common associates include cattail, reed canarygrass (Phalaris arundinacea), sedge (Carex spp.), bulrush (Scirpus spp.), rush (Juncus spp.), and willow (Salix spp.). Purple loosestrife can tolerate a wide range of conditions (up to 50% shade), can grow on calcareous and acidic soils (Rutledge and McLendon) and will even grow in standing water. Distribution: In Colorado, purple loosestrife is known to occur in the Denver/Boulder area and downstream along the South Platte River, in Mesa County along the Colorado River, in Montrose County near Nucla, in Otero County near the Arkansas River, and in Colorado Springs. It is not known if purple loosestrife has upper elevational limits, but since it grows successfully in Canada, it should be considered a threat at higher elevations in Colorado. Historical: Purple loosestrife is a native of Eurasia and was first recorded in America in 1814 (Bender and Randall 1987). Biology/Ecology Life cycle: Purple loosestrife begins its growth about a week to 10 days after cattail and reed canarygrass. Spring established seedlings grow rapidly and produce flowers 8 to 10 weeks after germination. After flowering, each stem supports a dense spiraling row of dark-brown seed capsules. Mode of reproduction: Purple loosestrife is a perennial that reproduces by seeds and rhizomes. The rootstalk of purple loosestrife is the main organ of local propagation; therefore, wide vegetative spread is unlikely. However, detached root or stem fragments can take root and develop into flowering stems (FEIS 1998). Seed production: A single flowering stalk can produce 300,000 seeds, and densities as high as 80,000 stalks per acre have been recorded (FEIS 1998). Seed bank: Purple loosestrife seeds may remain viable for up to 20 years. Dispersal: Seeds are mainly distributed by water, but can also be dispersed by animals and humans. Seeds do not drop from capsules until the air temperature becomes cold in the early fall. Integrated Management Summary Loosestrife populations which extend over three acres are difficult to eradicate and may be a better target for containment rather than control (Rutledge and McLendon). The key to effective control is early detection when infestations are small. It is fairly easy to control small numbers of loosestrife plants when the seed bank in the soil is small. Eradicating large populations with huge populations is much more difficult. Biological control should primarily be considered when populations of loosestrife have become large or are inaccessible. Small loosestrife infestations should be eradicated by hand-pulling or herbicide application. References
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