Purple Loosestrife

Purple Loosestife Control Guide

The purple loosestrife is an erect perennial with opposite or whorled leaves, its thick taproot supports up to 50 stems that can reach a height of 6 feet. The purple loosestrife is an aquatic to semiaquatic plant with a distinctive purple flower that makes it easy to recognize. This invasive plant thrives in marshes, wet meadows, streams, river banks, lake shores, and ditches. It can also survive in drier conditions.


The purple loosestrife extended flowering season allows it to produce vast quantities of seed that can easily spread to large areas. Early management to avoid large invasions is the best prevention.

Physical/Mechanical Control

Small infestations with younger plants (1-2 years old) can be hand-pulled. Plants more than 2 years old should be dug out with special care, their entire root system must be removed from the ground; all plant material should be bagged and disposed of. Mowing is not recommended because it will contribute to seed dispersal and seed bank exposure if the mower scrapes the soil. Physical removal, when used in conjunction with chemical control methods, will maximize success.

Chemical Control

In areas with less than 100 plants, a spot application of Shore-Klear is recommended. The plants should be cut about 6 inches above the ground. Apply a solution of Shore-Klear and Cygnet Plus directly to the cut surface.

If the purple loosestrife covers a large area, a foliar spray of Shore-Klear and Cygnet Plus should be applied just when plants have begun flowering. Where possible, flower heads should be cut, bagged and removed from the site before application to prevent the spread of seeds.

Shore-Klear is a systemic herbicide that will translocate down into the root systems killing the plant. Successful shoreline weeds management in heavily infested areas can take several years and sometimes annual maintenance spot treatments.

Cygnet Plus is a nonionic wetting agent, sticker, activator, and penetrant all in one. Cygnet Plus increases the effectiveness of herbicides uptake into the plant tissue.