SALEM, Ore. -- A pesticide typically applied by farmers and golf course managers to kill rodents has been linked to the recent die-off of more than 65 Canada cackling geese at a private lake in Keizer.

ODFW/kgw.com photo

One of the dead geese, as shown in a photo from the Oregon Department of Fish & Wildlife.

Five of six samples taken from goose carcasses tested positive for zinc phosphide, according to results from Michigan State University's Center for Integrative Toxicology.

Zinc phosphide is used to control voles, mice and ground squirrels, particularly in grass fields where rodents damage crops, state officials said Monday. When zinc phosphide is ingested, it is converted by stomach acids to phosphene gas, which attacks the heart, kidney and liver.

Classified as a restricted use pesticide, zinc phosphide can only be sold at licensed facilities, said Dale Mitchell, assistant administrator of the pesticides division of the Oregon Department of Agriculture.

Mitchell said the agency is tracking pesticide sales in the Keizer area to determine where the pesticide was applied, and whether it was done legally.

"Number one, we want to make sure that the materials are being used according to label directions", Mitchell said. "And number two, if there is a misuse of the product, contrary to label instructions, then we need to communicate that to the parties."

Large die-offs of Canada geese also occurred at Staats Lake in 2000, 2001, 2005 and 2007, newspaper reports indicate.

Previous investigations tied the bird fatalities to pesticide contamination and aspergillosios, a respiratory disease contracted from eating moldy grain and a frequent cause of geese deaths in the Willamette Valley.

Mitchell said zinc phosphide was linked to bird deaths of 2005, and the agriculture department notified farmers about the consequences of misusing it.