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Buyer bee-ware.

That's the bottom line of a recent study claiming that many plants touted as "bee-friendly" are actually deadly, because they've been pre-treated with pesticides shown to harm and kill bees.

The study, released by Friends of the Earth-US and co-authored by the Pesticide Research Institute, found that seven of 13 samples of garden plants bought at some large national retailers in Minneapolis, Washington, D.C., and the San Francisco Bay Area contained neonicotinoids, a widely used class of neurotoxic pesticides believed to be a factor in widely publicized global bee die-offs, or colony collapse disorder.

That may mean planting coneflowers or bee balm to attract pollinators including bees won't do them any favors.

"So-called 'bee-friendly' garden plants contain pesticides that can poison bees, with no warning to gardeners," said Lisa Archer, director of the Food and Technology Program at Friends of the Earth-US. "Bees are essential to our food system, and they are dying at alarming rates. Neonic pesticides are a key part of the problem we can start to fix right now in our own back yards."

Friends of the Earth recently sent letters to Lowe's, Home Depot, Target and other retailers, asking them to stop selling neonicotinoids and plants pre-treated with the pesticides.

"We haven't reviewed the study yet," said Home Depot spokesman Stephen Holmes. "But we certainly appreciate the importance of the bee population and we'll be reaching out to the study groups to learn more about their findings and methodology."

The use of such pesticides is much more widespread than most home gardeners realize, according to Heidi Heiland, owner of Heidi's Lifestyle Gardens, a Plymouth-based company that designs, installs and maintains gardens and landscapes. Because Heiland, like most home gardeners, purchases plants from growers, she's said she's very concerned about the presence of neonicotinoids in plants she buys.

Landscape Alternatives, a native plant supplier in Shafer, Minn., grows all its own plants and uses no neonicotinoids, said owner Roy Robison.

"That's one of the advantages of native plants," he said. "They don't have all the pests and diseases that fancy cultivated plants can get."

Robison does sometimes treat plants with insecticidal soap, a selective insecticide that kills some insects, such as aphids, by suffocating them rather than attacking the central nervous system. The residue is not harmful to pollinators, he said.

That can't be said of neonicotinoids. "They remain in plants and soil and can continue to affect pollinators for months to years after the treatment," said Timothy Brown of the Pesticide Research Institute. □

Kim Palmer • 612-673-4784