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Water Weed

Delta boaters have been tangling with a bumper summer crop of egeria densa - an exotic aquatic weed from South America whose shoots can grow up to eight feet long and whose spread has been exacerbated by the drought. While programs to unclog waterways of its weedy cousin - the water hyacinth - have been fairly successful, egeria presents more complex management problems. The hyacinth floats on the surface, so herbicides can be sprayed directly onto it. But egeria is entirely submerged, so Komeen - the herbicide being considered for its control - must be injected into the water. Komeen contains copper.

"You're creating a plume of copper that could kill other aquatic organisms and build up in the sediments," says Rudy Schnagl of the Central Valley Regional Board, which has a mandate to control copper loadings to the Delta. Schnagl is now working with California's Departments of Boating and Waterways and Pesticide Regulation on the problem, but he says it will be a difficult issue to get agreement on.

When the Board monitored spraying of the herbicide 2,4-D on the water hyacinths, it found no concentrations of concern in the water. Results from pilot tests on the egeria with Komeen - tests conducted this July by Dr. Lars Anderson of the U.S. Department of Agriculture - will soon be available. "We're looking at how long the copper lasts in the water column, how much gets into the weed, and whether it controls the egeria," says Anderson. He adds that while there are effective herbicides that aren't copper-based, none are currently registered for use in California.

Contact: Rudy Schnagl (916)255-3101

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