Spread of wingleaf primrose-willow ( <i>Ludwigia decurrens</i> ) in Northern California

Abstract Wingleaf primrose-willow [ Ludwigia decurrens Walter] is a pervasive rice ( Oryza sativa L.) weed native or naturalized to South America, the Caribbean, and the southeastern United States. While it was first noted in California in 2011 and provided with the highest pest rating “A” by the California Department of Food and Agriculture, enforcing eradication or quarantine was relatively disregarded, and it did not appear to spread significantly past its initial infestation area. Here, we report the spread within four counties (Butte, Placer, Shasta, and Tehama) of California, for which it has been found up to 184 km away from the initial infestation, and the expansion of the initial infestation within Butte County. As L. decurrens is already a problematic rice weed in parts of Asia, Africa, India, and the United States, monitoring new infestations is pivotal to prevent negative economic and environmental consequences to California and the United States.