In the California Delta, aquatic-weed treatment efficacy depended on habitat, dose and treatment history
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
View original evidence ↗
A landscape-scale retrospective found low-dose repeated applications often ineffective, especially in channels, while some slower-water habitats retained stronger control.
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