The Enemy - This aquatic perennial plant has stolons, that is, the plant can spread by broken plant parts which can start new plants. This plant has been determined to be the biggest invader in the U.S. The main areas of concern are near any of the 1200 hot springs that exist throughout the state. This plant has a very waxy cupped shaped leaf and produces a lavender and yellow flower. In 2011 it was found in the Snake River in the Thousand Springs area, thus it is now illegal to sell or grow.
The Attack - It is an emerged free-floating plant, which means that it floats above the water surface. The weed completely covers the water surface, thus choking out all other vegetation and creating great habitat for mosquitoes. This not only removes food for fish, but can cause problems with irrigation and creates more stagnet water. And don’t even think about getting a boat into the water as it will stop a propeller and plug up a jet boat.
The Defense - As this is a perennial mechanical harvesting/dredging is possible. As with most noxious weeds, this one will probably not be noticed until it is a large, serious problem. Once it reaches an epidemic state then using herbicides such as Renovate will control it. Application is very difficult without an airboat and should be applied when the plant is actively growing. There are numerous biological control insects that feed on this plant. Always make sure that your watercraft and trailer are free from ‘hitchhikers’ when you pull out of a launch site to ensure that you are not going to take plants from one water body to another. If you think that you have it, call for proper identification and consider environmental issues when trying to treat.
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)