In the California Delta, aquatic-weed treatment efficacy depended on habitat, dose and treatment history

A landscape-scale retrospective found low-dose repeated applications often ineffective, especially in channels, while some slower-water habitats retained stronger control.

Wild Lands Ecological Intelligence Editor
Wild Lands Institute · 24 September 2026

Evidence: Peer-reviewed
Geography: Sacramento–San Joaquin Delta, California, USA
System: Tidal freshwater estuary / invasive floating aquatic vegetation

WHAT THE EVIDENCE SAYS

Across 349 sites in 2004–2008 and 333 sites in 2014–2018, higher per-visit herbicide doses generally reduced floating aquatic vegetation more than the same seasonal amount spread across more low-dose visits. Effects varied sharply by habitat; channel treatments were weak or short-lived, while glyphosate effects persisted up to three years in some flooded-island sites.

WHY IT MATTERS / OUR READ

The management signal is spatial and operational: treatment method cannot be separated from flow environment, dose and repeated-use history.

CAVEATS / UNCERTAINTY

This is a retrospective program evaluation, not a randomized experiment, and it evaluates target-plant efficacy rather than full ecological safety, non-target effects or long-term resistance. The historical treatment periods also limit direct transfer to present programs.

SOURCE

Environmental Management
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