What a difference a spray makes. The first year of a water weed eradication program in the Laguna de Santa Rosa that used a combination of herbicide and heavy equipment showed signs of success, despite costing more than expected, officials said.
Crews removed about 5,300 tons of Ludwigia that was choking flood-control channels near Rohnert Park and wetlands near Sebastopol, about half the amount targeted in the five-year program.
Multiple applications of the herbicide glyphosate, tracked by a high-tech global positioning system, had about a 75 percent kill rate . Testing turned up no appreciable levels of groundwater contamination.
"We made a dent in it, but there's still a lot more there," said Julian Meisler, restoration project manager for the nonprofit Laguna Foundation. "We learned it's a very large undertaking."
Ludwigia, considered a menace to wildlife and a breeding ground for mosquitoes that could carry West Nile virus, was discovered in the laguna about a decade ago, flourishing in part because of higher water temperatures, nutrients from run-off and accumulating sediment.
It multiplied quickly, suffocating native plants, hurting water quality and blocking the passage of spawning salmon.
The tight-packed weed provided cover for mosquitoes, thwarting efforts to control them and prevent the spread of West Nile virus.
About two years ago, foundation officials, in partnership with state and local government agencies, sought money to try to kill Ludwigia in two laguna trouble areas - between Occidental and Guerneville roads west of Santa Rosa and in flood channels near the intersection of Rohnert Park Expressway and Stony Point Road.
Officials estimated the two spots held about 10,000 tons of the plant.
Work began in July, when a Martinez-based contractor began spraying the herbicide, chosen because it is less likely than others to pollute water, officials said.