Invasive weed may get whacked |

Invasive weed may get whacked

The U.S. Department of Agriculture is awaiting approval of an herbicide that targets a weed running rampant at the Tahoe Keys — the Eurasian water milfoil.

Water quality experts at South Shore last year rejected a proposal from the USDA to test two herbicides in limited areas at the Keys. They said the proposal was not detailed enough.

“We have a new proposal,” said Lars Anderson, who studies exotic and invasive plants for the USDA. “A new herbicide will be approved shortly, this month or next, that’s extremely effective against the Eurasian water milfoil.”

The chemical, called Renovate, has a short life in the water and finds water milfoil while ignoring other aquatic life. It also kills down to the roots of a plant. The U.S. Environmental Protection Agency is expected to approve the herbicide sometime in October, Anderson said.

Getting permission to use a chemical in Lake Tahoe is difficult. The Lahontan Regional Water Quality Control Board requires that no residue be found in surface waters.

Anderson said he expects to deliver to Lahontan in November a proposal to test Renovate and two other herbicides. If the project is approved, he hopes to begin tests this spring and see how the chemicals react to the lake.

The water milfoil, first detected at the lake in the 1960s, is clogging waterways of marinas around Lake Tahoe Basin. The Tahoe Keys Property Owners’ Association pays about $80,000 a year for water tractors to mow the plant, which can snake around boat propellers and damage engines.

Doug Helgeson, water systems supervisor at Tahoe Keys, said water milfoil harvesters have been in use since May and will be needed through early November because it is a low-water year, which means added sunlight and greater growth in the plant.

Invasive weed experts say harvesting, or mowing, the plant helps it spread because a fragment of the plant as small as an inch can take root. Water milfoil has been found at more than 13 areas in the lake. The weed was likely brought to Tahoe in small parts on boats from outside the basin.

— Gregory Crofton may be reached at (530) 542-8045 or at

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