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Management Of Perennial Pepperweed
Perennial pepperweed (Lepidium latifolium) is an exotic species in the mustard family that is well-established in New England, the far western United States, and Mexico. This weed is well adapted to riparian and wetland areas and threatens hay and forage production from native meadows. Perennial pepperweed is a highly competitive species able to establish dense monocultures. In riparian zones, it interferes with regeneration of willows and cottonwood species (Young et al. 1995). The accumulations of semi-woody stems negatively impacts nesting habitat for wildlife (Young et al. 1995). The greatest threat posed by perennial pepperweed is to native hay meadows. The mode of invasion is along irrigation ditches from riparian areas. In the hay meadows perennial pepperweed lowers the quality of hay in terms of protein content and digestibility. In addition, many believe that perennial pepperweed can be poisonous. Most cases of suspected poisoning have occurred with horses being fed hay containing perennial pepperweed under confined conditions.
Mechanical Control
Due to the rhizomes of this perennial weed, mechanical control provides little or no control. In addition, the areas that this weed tends to grow (i.e. wetlands) are impractical for tillage. Research from the University of California has shown that mechanical top removal treatments does not reduce perennial pepperweed densities. Research from Colorado State University showed that handpulling or mowing controlled only 4 and 5% of perennial pepperweed.
Chemical control
In general, effective chemical control requires multiple applications. Timing and application rate are crucial for successful control. Again, application rate is critical; MORE DOES NOT NECESSARILY MEAN BETTER CONTROL. Always read the label when applying a herbicide. The label will be able to tell you how much to apply per acre. If you have any confusion as to how much to chemical to apply to your tank, please call our office and we will assist you as soon as possible.
Research conducted at Colorado State University found that Campaign (glyphosate + 2,4-D) at 54 oz/A controlled 100% of perennial pepperweed 3 months after treatments were applied. However, the glyphosate in Campaign will injure and kill perennial grasses and use of Campaign in successive years should be avoided. Escort (metsulfuron) applied at 0.75 to 1.0 oz/A or Telar (chlorsulfuron) applied at 1 oz/A are effective if combined with an agricultural surfactant at 0.25 % v/v (equivalent to 1 qt of surfactant per 100 gallons of spray solution). The optimum time to apply Escort and Telar for perennial pepperweed control is in the spring when it is flowering or in the fall. These herbicides can be purchased at an agricultural products supplier (please check the yellow pages for specific stores).
Biological Control
No effective agents for Colorado at this time, however, research in this area persists.
Cultural Control
Perennial pepperweed might be managed temporarily with herbicides or, in the future, with insects, but long-term reductions must include planting competitive plant species to occupy bare ground once infested by the weed. Many improved grass species can be seeded in late fall or winter when seedbeds are properly prepared. An initial herbicide treatment is important to suppress problem perennial weeds before seeding.
Important grass characteristics to be considered for long-term control of problem weeds such as perennial pepperweed include 1) adaptation to the soil and climate; 2) ease of establishment; and 3) competitiveness with weeds.