Purple Loosestrife (Lythrum salicaria) 

Purple loosestrife is an exotic, invasive, perennial plant that is spreading rapidly in North America.  Purple loosestrife is native to Europe and Asia, and was introduced to North America in the early 1800’s.  Purple loosestrife has infested many lakes in Wisconsin including the Chippewa Flowage.  Thick stands of purple loosestrife can choke out native vegetation such as, manoomin, or wild rice.  Manoomin is important culturally and spiritually to the Lac Courte Oreilles Ojibwe Tribe.  Thick stands of purple loosestrife can also reduce food, shelter, and nesting sites for wildlife, birds, turtles, and frogs.  Waterfowl and muskrats can especially be affected. 

Purple loosestrife forms dense monoculture stands sometimes hundreds of acres in size, which can threaten the biotic integrity of wetland ecosystems.  Purple loosestrife produces around 2.7 million seeds per plant.  With 2.7 million seeds per plant and few natural enemies it is no wonder that purple loosestrife is taking over many Wisconsin wetlands.

Click here for Purple Loosestrife Distribution on the Chippewa Flowage in 2005

Purple Loosestrife in full bloom. (Photo: Erik Olson)

Purple Loosestrife in late fall.  (Photo: Erik Olson)

Purple Loosestrife on County HWY CC.  (Photo: Erik Olson)

Control  

There are many different control techniques.  Mechanical, biological, and chemical are the main means of control, and all three have been used on the Chippewa Flowage.  Mechanical control is the removal of either the entire plant (including roots), or the cutting off and bagging of the flower or seed head.  Mechanical is a good control technique when used on smaller stands of purple loosestrife.  Chemical control is the use of herbicides.  Oftentimes chemical control is used with mechanical.  There are some downfalls to using herbicides in an aquatic ecosystem.  Biological control is the use of beetles or weevils that are introduced into a thick stand of purple loosestrife where it feeds on the plant’s leaves, flowers, seeds, and roots.  However, these beetles and weevils need good dry ground cover in order to over winter, so some wetland environments are not suitable.   

Beetle Damage!  (Photo: Erik Olson)

Identification  

Gardeners, waterfowl hunters, and other outdoor enthusiasts should know how to identify purple loosestrife – detecting new infestations can prevent the spread of this plant.  

 Here are some good sites for purple loosestrife identification.

Purple Loosestrife "Look-A-Likes"

Diagram: USGS

Polygonum amphibium    (Water Smartweed)  (Photo: Erik Olson)

Asclipias incarnata (Swamp Milkweed) (Photo: Erik Olson)

Pontederia cordata (Pickerel Weed)  (Photo: Erik Olson)

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