The Enemy: Purple loosestrife (Lythrum salicaria) is a semi-aquatic perennial plant that is native to Europe and can still be purchased as an ornamental. This plant out-competes native habitat along waterways and has no value to wildlife such as waterfowl for food or shelter. This plant can produce over 2.5 million seeds per year and can totally destroy river and ditch banks by impeding water flow. It is a woody plant that can grow to a height of 8 feet and for the most part has to have its roots in moist to wet soil. It produces a beautiful flower that grows up the top foot of the woody, four sided (square) stem. It blooms from mid-July to mid-August.
The Strategy: Purple loosestrife can be found along the Henrys Fork of the Snake River in Madison County down river to where a few plants have been found at the upper power plant of Idaho Falls Power. We have also harvested a couple of plants just across from the observation deck of the falls.
The Defense: Controlling Purple loosestrife is a challenge due to them growing in and near water. Digging them up can be done with a lot of effort but remember to try to get most of root as it will grow back if some roots are left behind. There is a limited amount of herbicides that can be legally used over water to help control the weed. These include specialized herbicides such as Habitat, Rennovate, Aquamaster, or Weedar 64. One of the best tools for this weed is the use of a defoliating beetle, the Galerucella, that only attacks the Purple loosestrife plants. This bug has done a great job of removing these plants.
To discover more about biological weed control, visit the Nez Perce Bio-Control Center website at www.nezpercebiocontrol.com
Please do not purchase this plant from magazines and internet sources and if you think you have seen it please call your local County Weed Supervisor and keep you properties healthy and weed free.
ERADICATING PURPLE LOOSESTRIFE
PLEASE NOTE - The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.
For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.
U of I Idaho's Noxious Weeds Control Guidelines (183 KB PDF download)