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December 12th, 2015

12/12/2015

Purple Loosestrife- Pretty but Problematic

Exotic species affecting lakes have been the focus of our Tip of the Month newsletters each August. This "Tip" highlights that pretty, purple invader of lakeshores and wetlands - purple loosestrife.
What does it look like?
Purple loosestrife (Lythrum salicaria) is easy to spot when in bloom. The bright magenta flowers form a long stalk at the top of the plant and bloom from July to September. The plants can grow from 2-6 feet tall with many branches at the top and a square stem. The leaves are long and narrow with pointed tips, smooth edges and heart-shaped bases usually arranged opposite on the stem but can be in whorls of three. This species grows in moist to saturated soils along shorelines, wetlands, ditches and floodplains in partial to full sun.
How did it get here?
Purple loosestrife is native to Eurasia, extending as far north as southern Sweden and Finland and south to the Mediterranean basin in North Africa (Michigan Sea Grant). The plant was likely introduced to the northeastern U.S. in the 1800s when sediments containing purple loosestrife seeds were used in ships' ballasts. Upon arrival to the U.S. eastern seaboard, these sediments were deposited in ports to make room for cargo. The species then migrated inland along rivers, canals and ditches. Purple loosestrife was also used for ornamental and medicinal purposes.
What are the management options?
Purple loosestrife management typically falls into three categories: mechanical, chemical and biological. All methods require vigilant, multi-year efforts.

Mechanical: This method involves physically removing the plant and can be effective for small infestations. The entire plant should be removed before seeds develop on the flower head. Removal after seeds develop will spread the seeds. All plant fragments should be bagged and removed from the site.
Chemical: Herbicides can be effective in treating populations of purple loosestrife where hand pulling is not feasible. Glyphosate-based products are effective but are non-selective and can harm other desirable plants. If possible, flower heads should be removed prior to herbicide treatment to avoid additional seed dispersal.
Biological: There are 120 plant-eating insects associated with purple loosestrife (MI Sea Grant). Of those, the leaf eating beetle, Galerucella sp., has proven to be the most promising for controlling purple loosestrife in the U.S. In 1994 the MichiganDepartment of Natural Resources released these beetles in the Saginaw Bay region. The Galerucella beetle is now being widely used in areas seeking alternatives to mechanical and chemical control. Both the larval and adult beetles attack purple loosestrife causing extensive leaf damage, decreased flower (and seed) production, and stunted growth. A root boring weevil, Hylobius transversovittatus, has also been released in Michigan with lesser success.
What should I do if I find purple loosestrife?
For small infestations, hand digging, bagging and disposal is the preferred option. If the population is too large to physically remove, chemical herbicides approved for use near aquatic systems can be used in some situations, although native vegetation can also be affected. The introduction of the Galerucellabeetles to an infested area can provide targeted control while not impacting desired native vegetation. Beetles can be purchased through vendors or collected and moved from a donor site with an established beetle population. K&A maintains beetles on an annual basis for its stream restoration sites and client needs.

http://mtweed.org/weed-of-the-week-purpleloosestrife/
Article from Kaiser & Associates, LLC (http://www.kieser-associates.com/)

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December 12th, 2015

Lake of the Woods in SW Michigan