Purple Loosestrife

Lythrum salicaria

What is it?

As quoted from Colorado State University Extension Website on Gunnison County Noxious weeds: Purple Loosestrife (Lythrum salicaria) is a non-native, tap-rooted, perennial forb. It is native to Europe and was introduced to North America as an ornamental plant for gardens. It has escaped into natural areas such as stream banks and shallow ponds. Purple Loosestrife reproduces primarily by seed. A single, mature plant can produce up to three million seeds per year. The seeds can remain viable in the soil for 5 to 20 years. Pieces of roots or stems also can produce new plants. Purple Loosestrife produces multiple four-sided stems that can grow two to eight feet tall. Leaves are two to five inches long, lance-shaped and whorled on the stems. Flowers are tightly grouped in long, vertical heads; they bloom from the bottom up. They are pinkish-purple in color, about one inch long, and have five to seven petals. Flowers appear from late June through September.

This invasive is native to Eurasia and was first recorded in the U.S. in 1814.

Why is it a problem?

Purple Loosestrife is found along river banks, ditches, and wet meadows, throughout the state, and in particular in the Gunnison Basin. Infestations grow rapidly and can replace native vegetation, and log water flow in canals and ditches. Additionally, the invasive has little wildlife habitat value. Infested areas, such as wetlands, eventually become a monoculture of loosestrife.

Management techniques:

The most effective way to manage Canada thistle is by combining methods of control:

According to the CSU Extension CSU extension link to Purple Loosestrife, the most important control method is considered to be prevention.
If you find Purple Loosestrife in your garden, it is best to remove the plants immediately. Some, great native substitutes are: Spotted Gayfeather, Rocky Mountain Penstemon, Beebalm, Purple Coneflower, and Colorado Columbine
The key to control of this invasive is early detection and dealing with the infestation when it is small, and seed have not yet taken hold.
Larger populations are harder to deal with, but persistent monitoring and management of sites can ensure eradication over the long term.
Purple Loosestrife is designated as “List A” species on the Colorado Noxious Weed Act. It is required to be eradicated wherever found in the State. For more information visit www.colorado.gov/ag/weeds and click on the Noxious Weed Program link or call the State Weed Coordinator at the Colorado Department of Agriculture, Conservation Services Division, 303-239-4100.
Biological agents are not included in the List A species under the Colorado Noxious Weed Act. Eradication is the prescribed method for management.

What can we do?

The most important thing you can do is learn to identify the Purple Loosestrife and remove it before it adds more seeds to the seed bank. You can manage the plant before it flowers, or cut its flowers and despose of flowers heads before seed set. Also using herbicides and following up on the site later in the season and for years to come are helpful tools. Here are ways you can identify the Purple Loosestrife:

Showy pinkish-purple flowers bloom in long vertical racemes.
Lance-shaped leaves have smooth edges.
Four sided stem.

General Information on Purple Loosestrife:

National Park Service

This PDF covers information from the U.S. Park Service on their management plan for Purple Loosestrife.

Colorado State University Extension

Provides lists of problematic, invasive weeds on their main website. This PDF covers background information and management techniques.

Colorado Weed Management Association

This organization has done extensive research on Purple Loosestrife including its biology and management. Here is a link to their research on the weed.