Purple Loosestrife – A Noxious Weed

Recently, some folks pulled into the local nursery, asking about the pretty pink flowering plants that were blooming along the fields and roadsides. They wanted to purchase some of those plants for their garden. What they were seeing was purple loosestrife, Lythrum salicaria. This invasive weed is misleading, as we typically think of pretty things as good. Native to Europe, this loosestrife has been grown in the US as a garden plant. It was used for medicinal purposes as well as forage for bees and as an ornamental plant. It has now become a noxious weed across the US, particularly in the Northeast.

Purple loosestrife is found along waterways, marshes, and wetlands. It prefers sun, but, like most invasive weeds, it adapts well to many soil types. It grows into dense plantings and reduces then eliminates wildlife. Unfortunately, this plant is not liked by birds, mammals, or waterfowl. As the waterways are taken over by this single plant species, less and less habitat is available for our native wildlife to nest, eat, and breed.

It can take over a site very quickly. It not only reduces our native food supply and habitat for our wildlife, it also reduces water flow through areas, causing water quality to decline, increasing costs for dredging those waterways.

Unfortunately, there are no natural predators, specifically insects, diseases, and animals that attack the purple loosestrife. This makes the plant even more prolific in our wetlands. In Europe, Lythrum's native habitat, there are natural predators for this plant, keeping it in check, just as our native plant populations are kept in balance by natural predators here.

How can we control this plant? Pennsylvania has declared loosestrife as a noxious weed. The inclusion of loosestrife cultivars was added to the noxious weed list in November 2000. This means that "it is illegal to propagate, sell, or transport these weeds in the Commonwealth" (PA Bureau of Plant Industry). This is to prevent further spread of this invasive plant.

Ways to Prevent Further Spread of Loosestrife

• Do not plant it. Even Lythrum varieties advertised not to make seeds can cross-breed with the invading loosestrife to make seeds.
• Be on the lookout for pioneering plants or isolated small colonies, especially in areas otherwise free of loosestrife. Remove pioneer plants immediately.
• Rinse off equipment, gear, clothing, and footwear used in infested areas before moving into uninfested areas.
• Cut off flower heads, bag and destroy them. Repeat throughout the flowering season (late June - early September). This will prevent millions of seeds from ripening and spreading."

~ PDA Bureau of Plant Industry

If you have existing plants, you need to control them. Do not let the pretty flowers fool you. For young plants, just pull them, bag and destroy the plants. You can dig older plants, but must be sure to remove all the roots, as remaining roots will sprout. If you are cutting them, the cut stems will just sprout new shoots and roots, creating even more of a problem.

Take this noxious weed seriously. Purple loosestrife may be beautiful in the garden, but the potential degradation of our wetlands because of this invasive plant is great. Look for other alternatives in the garden.