Control Costs, Operation, and Permitting Issues for Non-chemical Plant Control: Case Studies in the San Francisco Bay-Delta Region, California

The state of California recommends that aquatic pesticide users obtain NPDES permits in response to recent legal decisions by the U.S. Ninth Circuit Court of Appeals. Due to the high cost of NPDES permitting, nonchemical aquatic plant control methods are receiving renewed attention in California. Five case studies were evaluated to determine cost and implementation issues for alternative plant control methods in waters of the San Francisco Bay-Delta region. The primary case study examined control costs, operation, and endangered species permitting for mechanical shredding of water hyacinth (Eichhornia crassipes) in the Sacramento-San Joaquin Delta. Additional case studies examined control costs for the use of backhoe excavators, manually operated weed-trimmers, or grazing by goats (Copra hircus) to control submersed, emergent, or riparian vegetation. In the fall of 2003 and the spring of 2004, three types of shredding boats were operated on two representative sites. Two boats were operable in all conditions, provided there was sufficient water depth (> 0.3 to 0.6 m). A third boat was difficult to maneuver, could not chop large plants, and repeatedly got mired in dense vegetation. Treatment costs varied widely as a function of plant size. In the fall, costs in three of the four sites were greater than $4,000/hectare (ha). In the spring, treatment costs ranged from $477 to $2,146/ha, comparable to chemical herbicide application. Control costs also varied widely among the other case studies, ranging from $456/ha for goat grazing on riparian vegetation to $24,200/ha using manually operated weed-trimmers to control cattails (Typha latifola) and bulrush (Scirpus acutus).