Giant Reed (Arundo donax)
Background
Arundo donax, also referred to as Giant Reed, is a tall, invasive perennial grass that forms dense stands in riparian areas, wetlands, and disturbed sites throughout California, including major watersheds in Ventura County. It displaces native vegetation, consumes large amounts of water, increases wildfire risk, and can obstruct waterways and reduce flood conveyance capacity. Arundo is considered one of the most damaging invasive plants in the state and coordinated removal efforts are underway in coastal watersheds including within Ventura County.
Problem
Weeds are a serious threat to Ventura County’s natural resources and agriculture. A limited number of non-native plants are classified as noxious and invasive because of their aggressive, competitive behavior. Arundo donax currently has the greatest negative impact of any invasive weed in the county, affecting the environment, agriculture, flooding, water supply, fire risk, and local communities’ connection to nature. The VCWMA voted it the county’s number one invasive weed in 2019, and the 2025-2026 Ventura County Grand Jury more recently emphasized this ranking, citing its significant environmental impact, including its role in fire.
Solution
The VCWMA is working with its partners, local watershed groups, and others to support aquatic weed removal projects in the Ventura River, Santa Clara River, and Calleguas Creek watersheds, currently focusing on Arundo donax and Tamarix spp. These efforts include developing Early Detection Rapid Response projects that target Arundo donax in upper watersheds with few plants, previously cleared sites that have become reinfested, recently burned sites, and sites where Arundo donax debris has accumulated after storm events. They also include proactive outreach and education for agencies and property owners in affected or high-risk areas, covering the severity of the problem, how to detect infestations, best practices for eradication and control, and applicable laws and regulations.