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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.

Heavy equipment mounted on pontoon boats followed, scooping dead Ludwigia from the channels.

When work ended in October, crews had removed 5,388 tons of the invasive weed, mostly from the channels.

About 85 percent of the dead material at the Occidental Road wetlands was not removed for fear that heavy equipment would damage the land, Meisler said.

Spraying proved effective, although penetrating the thick web of weeds was difficult.

There were signs of rapid regrowth, which will add to costs, Meisler said.

Water quality was good throughout the job. Levels of herbicide, tested five days after every spraying, were 96 percent below federal standards, he said.

Work in the first year cost $900,000, about 1? times more than projected.

Officials underestimated the time required to spray and remove the densely growing plant, which covered 120 acres at the two locations, Meisler said.

Also, water-quality monitoring required by the government to screen for traces of herbicide topped $100,000, twice as much as expected, Meisler said.

Depending on the amount of Ludwigia regrowth, the foundation might need more money to complete the project, budgeted at $1.5 million.

"The fact that there was no work done until this year made it much more expensive and labor-intensive," Meisler said.

How much more money the project will need won't be known until April. Meisler said the amount could be in the hundreds of thousands of dollars.

The removal also dredged up old car tires, furniture and pieces of an old pickup, Meisler said.

"Everything you can imagine has been thrown in that laguna," Meisler said. "We hauled it away."

Mosquito-control officials were pleased with the first-year results, saying testing showed the work reduced the number of flying pests.

Jim Wandersheid, district manager for the Marin-Sonoma Mosquito and Vector Control District, said traps that routinely caught thousands of mosquitoes before the work were only netting a few dozen.

And with the channels clear, Wandersheid will be able to use boats instead of helicopters this year when the district does mosquito spraying, saving time and money.

"Ludwigia becomes a really nice home for mosquitoes. It protects them," said Wandersheid, whose district put up $100,000 for the project. "Because the weed is actually removed now, our job is going to be a lot easier."