Effective Fennel (Foeniculum Vulgare) Control with Herbicides in Natural Habitats in California

Fennel is a major invasive plant in many lower elevation natural areas in coastal California. Three identical field experiments were conducted to evaluate glyphosate and triclopyr for control of fennel. Treatments included each herbicide applied alone and in various combinations. We also compared broadcast applications to spot spraying of individual fennel plants because spot spraying is a commonly used technique in natural area weed management. Most treatments controlled fennel well when evaluated 6 wk and 1 yr after treatment, with the exception of the lowest rate of glyphosate. Purple needlegrass, a native perennial grass, was present in two of the sites. In most, but not all, treatment and site combinations, it was not significantly harmed by the herbicides. The spot spray applications were less effective and used more herbicide per unit area than the broadcast spraying. Nomenclature: Glyphosate; triclopyr; fennel, Foeniculum vulgare P. Mill. FOEVU; purple needlegrass, Nasella pulchra (A. S. Hitchc.) Barkworth