Rogue of the Month: Purple Loosestrife, the Scourge of Native Wetlands
Target: Purple loosestrife, Lythrum salicaria aka spiked loosestrife
Designated a “Restricted” invasive wetland perennial by the DNR, purple loosestrife permeates the Northwoods. Commonly found in meadows and wetlands, purple loosestrife is found in 48 of Oneida County’s and 57 of Vilas County’s DNR-counted water bodies.
Its adaptability and penchant to crowd nearby plants make it a threat to native wetland plants. As a sedge, purple loosestrife is particularly hardy and fecund — one mature plant has roughly 50 stems and that plant is capable of producing 2.7 million seeds annually. It should go without saying, you want to remove this plant before it goes to seed!
Purple loosestrife’s survival in Wisconsin has seemingly depended upon its ability to pass for native perennials winged loosestrife (Lythrum alatum), swamp loosestrife (Decodon verticillatus), blazing-star/gayfeather (Liatris spp.), fireweed (Epilobium angustifolium) and blue vervain (Verbena hastata). But that changes now, reader, should you accept the assignment to eliminate this foe.
Purple loosestrife plants feature one leader stem with many auxiliary stems. Young plants are smaller (8 to 12 inches) with fewer stems, whereas established plants will grow from 3 to 7 feet with upward of 50 stems. Each stem features lance-like leaves, which are stalkless and grow either as sets of two or whorls of three. Each stem contains numerous flower blossoms dotted among the leaves and clustering upward upon the stem. Individual flower blossoms contain five or six petals and range from pink to purple in hue. They tend to bloom in a bottom-to-top cascade from July to September.
Report infestations to the DNR, pull the plant and be sure to remove any roots, leaves or stem clippings during removal. Plants clipped back will simply grow back bigger and bushier, do not behead this violaceous hydra! Purple loosestrife is able to self-propagate from clippings left in the ground too. Bag all plant remains. Do not compost, mow or chip. Landfill or burn the bags.
Chemical controls — such as mazapyr or glyphosate — may be appropriate for infestations not too close to waterways but check local regulations and ordinances first, and larger infestations may require biological control on the part of the DNR.
For more information about this wily wetland rover, visit dnr.wisconsin.gov/topic/Invasives/fact/PurpleLoosestrife.
Rogue of the Month is a feature of Northwoods Pulse, your local news beat. Each month gardening columnist, Carly Ratliff, features a Northwoods pest and arms you with the information to identify and combat it. Have a pest you want covered? Submit ideas to Carly at carly.j.ratliff@gmail.com. NW Rogue submissions can be invasive species, common household or garden pests, weeds or any other unwanted guest.
About the Author: Carly Ratliff is a nearly lifelong resident of the Northwoods (30 years) with 14 years’ experience in publishing — first at the community newspaper in Eagle River and then for the water and wastewater trades. In her spare time, Carly is an artist specializing in fiber art and acrylic painting, enjoys bikejoring with her dog, and gardening. She is also a newly minted Master Gardener excited to swap gardening tips and tricks with readers.
