Integrated Management of Perennial Pepperweed (Lepidium latifolium)

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AbstractPerennial pepperweed is invasive throughout California. It thrives in a wide range of environments and is a common weed in floodplains, pastures, wetlands, and roadsides. In disturbed areas, perennial pepperweed rapidly forms monotypic stands with a thick litter layer. These infestations not only out-compete other vegetation, but prevent re-establishment of desirable species even after perennial pepperweed control. This experiment examined integrated management strategies with the goal of maximizing perennial pepperweed control and establishment of desirable native vegetation. The experiment was conducted at two sites in Lassen County, CA. Both sites were heavily infested with perennial pepperweed and lacked competing vegetation. The experimental design was a split-split-randomized block with four replications. Site preparation treatments included winter burning, summer and fall mowing, winter grazing, and fall disking. These treatments were designed to remove thatch to facilitate herbicide application and reseeding of desirable perennial grasses. Herbicide treatments included chlorsulfuron, 2,4-D, or glyphosate applied at the flower bud stage. Revegetation treatments included no seeding and no-till seeding of native perennial grasses. Most site preparation plus herbicide combinations reduced perennial pepperweed cover > 85% compared to the untreated control, although treatment efficacy was variable between sites and years. Burning, grazing, mowing, or disking in combination with herbicide treatment and no-till seeding was necessary for successful native perennial grass establishment. Burning or mowing with yearly 2,4-D applications for 3 yr gave the best combination of perennial pepperweed control and native grass establishment. Chlorsulfuron caused chlorosis and stunting to western wheatgrass, basin wildrye, and beardless wildrye at both sites when applied the spring before seeding. No treatment offered complete weed control, suggesting follow-up spot herbicide applications are needed for long-term perennial pepperweed suppression. These results provide several successful integrated strategies for control of perennial pepperweed and revegetation to a desired native perennial grass community.