Purple Loosestrife

Mature Purple LoosestrifePurple loosestrife (Lythrum salicaria) , a plant that is not native to Oregon, has invaded our waterways. Some folks think it's a beautiful plant but it is also an extremely invasive, aggressive weed. It was brought to the United States in the early 1800s as an ornamental plant and has spread throughout the northeast and midwest. Now it's a serious problem in the west and has been found in 25 of 36 counties in Oregon (including Jackson and Josephine Counties).

Purple loosestrife is a tall (up to 10 feet) perennial plant that has spikes of pink/purple flowers closely attached on an angled stem, mostly opposite leaves with edges attached to stem, a woody tap root and small roots that form a thick dense mat. One of the look-alikes of this plant is spiraea. This native of Europe blooms from July to September along wet areas, especially rivers, lakes, and irrigation ditches. A single plant can produce up to 3 million seeds annually which are transported by water and roots left in the ground can resprout.

Image Purple Loostrife flower and leaf structureSome nurseries in our area were selling this plant until they found out what a problem it can cause. The Oregon Department of Agriculture has prohibited the importation, sale, and distribution of purple loosestrife and its horticultural varieties. These varities are known by many names which include: Rose Queen, Purple Spire, Fire Candle, The Rocket, and Morden Pink.

The reason this plant is such a problem is that it can form pure stands that affect native wildlife and plants, agriculture, and wetland resources. Some specific examples of problems include: seeds not eaten by native songbirds, waterfowl avoiding loosestrife invaded wetlands, wildlife habitat diversity decreasing, loosestrife clogging irrigation ditches, invading wet areas in cultivated fields, and open waterways becoming clogged.

Limited surveys for this species have found populations along Bear Creek, the Rogue River (even the wild and scenic portion), and the lower reaches of the Applegate River. I think I saw some in an irrigation ditch between Murphy and Wilderville. Nabil Atalla, with the Medford District BLM, has a project planned this summer to fly low elevation flights over some of our major rivers (Bear Creek, Rogue River, Applegate River) when this plant is blooming to map these populations. We imagine some plants were washed out by the flood but since this plant can resprout from roots and the roots are pretty persistent, we expect to see plants reappearing along most previously known sites.

I haven't had much experience with this plant and as far as I know we don't have any in the upper reaches of the Applegate River. Some possible ways to help control it include digging (get as much of the root as possible) and cutting the flowers off to stop seed from forming. I would not suggest herbicides because these plants grow so close to the water in our main rivers. The Oregon Department of Agriculture is working on making insects available for release as biological controls.

If you find any locations of this plant report it Nabil Atalla (770-2396) or give me a call (Barb Mumblo 899-3800) .