Perennial pepperweed (Lepidium latifolium) is a potential threat to biodiversity and ecosystem function in the communities that it invades. The mechanism for its successful invasion of riparian and wetland environments includes reproduction via seed and root propagules and its ability to withstand long duration flooding and saline conditions once established. Controlling this species presents a number of challenges for land managers, including difficult property access, limited herbicide choice, and the varied success of weed control measures. In this study, we tested the efficacy of a nonchemical-modified tarp treatment, and compared posttreatment stem counts to herbicide treatments with Mow–glyphosate and chlorsulfuron in a wildland setting. We found that tarping applied in combination with a mow and till treatment was effective at controlling perennial pepperweed at levels similar to herbicide treatments with Mow–glyphosate and with Mow–chlorsulfuron. However, Mow–Till–Tarp treatment is extremely time consuming and has the potential to limit native plant community recovery.

Nomenclature: Chlorsulfuron; glyphosate; perennial pepperweed, Lepidium latifolium L. LEPLA

Interpretive Summary: Perennial pepperweed (Lepidium latifolium) threatens wildland and natural areas where maintaining existing biodiversity and restoring degraded sites is a key concern to land managers. Herbicides are an effective control technique for perennial pepperweed, but are not always feasible in natural areas. In this study we tested the implementation of two tarping techniques as nonchemical alternatives to glyphosate and chlorsulfuron herbicide use for controlling perennial pepperweed in riparian areas.

We compared the efficacy of Mow–Tarp and Mow–Till–Tarp techniques to Mow–glyphosate and Mow–chlorsulfuron techniques for controlling perennial pepperweed. This comparison showed that a tarp treatment, where an area is mowed, tilled, and then tarped, is effective at controlling perennial pepperweed infestations. This method can control up to 100% of perennial pepperweed under a tarped area and is comparable to Mow–glyphosate and Mow–chlorsulfuron treatments. In addition, we found that a Mow–glyphosate treatment is just as effective at controlling perennial pepperweed as a Mow–chlorsulfuron treatment 1 yr after treatment. The Mow–glyphosate method can be applied to emergent vegetation and can be less detrimental to the native vegetation than a Mow–Till–Tarp technique, which leaves behind exposed soil and can require subsequent restoration.