The Enemy - Perennial pepperweed (Lepidium latifolium) An perennial plant native to southern Europe and western Asia. This is one of these beautiful plants that was introduced into the country as an ornamental and now has become a noxious weed. It has very small white flowers that grow in small clusters at the terminal end of the shoot. The leaves are extremely waxy, with a prominent, whitish mid-vein. The plant has an extensive root system and grows thick enough that they will cover the ground an surrounding vegetation 100 percent. This plant resembles White top which grows early in the spring to a height of 18 inches at maturity, and the Perennial pepperweed is green throughout the summer with a height of 3 to 6 foot tall.
The Strategy - This plant will crowd any desirable vegetation in the course of a few years. Due to its extensive root system other plants cannot regrow in the area, furthermore the thickness of the above ground growth prevents the sunlight from reaching other plants. Many people find this plant attractive so they pick it, take it home, and then restart a problem on a new piece of property. Although this mustard is not toxic to animals they do not desire it as a forage.
The Defense - In eastern Idaho this plant is primarily found along our ditch banks and river. When this plant is newly established mechanical control can be effective. There are no biological control insects available right now, but the University of Idaho is working toward one as they are on the other mustards (Hoary Cress and Dyers Woad). Herbicides such as Telar® XP and Escort® XP are the products of choice. Many other products have been used with minimal success. In open fields and wastelands waiting until the plants are in the bud stage is the prime time to spray. Also by adding a silicone based surfactant will help spread the herbicide around the plant as well as penetrated through the waxy surface of the leaves. This plant looks like many of the mustards that grow everywhere so call you local weed authority to properly identify the plants.
ERADICATING PERENNIAL PEPPERWEED
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)