Lepidium latifolium • Class B

Perennial pepperweed normally grows 1 to 3 feet tall, but may reach heights of up to 6 feet tall. It has many stems emerging from a woody root crown.

Its alternate, waxy leaves are dark bluish green to grayish green in color with a whitish mid-vein. The lance shaped basal leaves are up to 12 inches long with long stalks. Stem leaves are smaller with short stalks.

Rounded clusters of small white flowers adorn the tops of its stems from June to September. 

The competitive nature of Perennial pepperweed poses a serious threat to many native undisturbed areas. Dense infestations of Perennial pepperweed can form near monocultures. Accumulations of its semi-woody stems degrade nesting habitat for wildlife, interfere with the regeneration of willows and cottonwood trees. Dense infestations degrade waterfowl nesting habitats. 

Since the roots do not hold soil well, pepperweed infestations can destabilize river and stream banks and increase soil erosion in valuable watershed areas. 

It displaces more desirable native species and poses a particular threat to natural areas and hay meadows. 

It is an aggressive non-native plant of the mustard family, which tends to establish and rapidly colonize pastures, riparian habitats, waste places, wet areas, ditches, and along roadsides. It can also be a problem in roadside, rangeland, and field cropland, and even dry habitats. In coastal areas, the plant invades brackish marshes.

Perennial pepperweed infestations can produce over 6.4 billion seeds per acre annually. 

• The best control measure for Perennial pepperweed is prevention. Do not collect Pepperweed flowers or plant material from the wild because it will likely lead to seed dispersal and new infestations.

• All classes of sheep or goats may be used as a weed management strategy. Repeated grazing for several years will suppress Perennial pepperweed long term. 

• Hand pulling is most effective for small infestations where the soil is moist and loose. A slow steady pulling action will remove 6 to 8 inches of root. However, new plants will sprout from any remaining root fragments. These areas will need to be monitored frequently and new growth pulled as soon as it appears. 

• Since Perennial pepperweed often grows near streams, ditches and salt-water estuaries, the use of an herbicide formulated for aquatic settings is required. Please note that aquatic herbicides are restricted for use in Washington State to licensed applicators only. 

• For terrestrial applications spot spraying with a product containing the active ingredient glyphosate is successful for controlling Perennial pepperweed in dry environments. The most effective time for treatment is when the plants are at bud to early bloom stage. In established infestations, woody stalks from previous growing seasons will need to be removed prior to herbicide applications in order to achieve effective coverage. The site will need to be re-checked in the fall and any re-growth sprayed to achieve control.  

• When using herbicides, always read and follow all label instructions and obey all label precautions. (Note: pesticide product registration is renewed annually and product names and formulations may vary from year to year.) 

• There are currently no biological control methods available. 

 Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels