More than 50 percent of all supposedly "bee-friendly" home garden plants sold at three of North America's top-volume plant retailers are, in fact, fatal to bees, says a new report from Canada.

Released by the Friends of the Earth environmental advocacy group, the report "Gardeners Beware 2014" asserts 36 out of 71 -- or 51 percent -- of all garden plant samples purchased at Home Depot , Lowe's and Walmart stores in 18 United States and Canadian cities had been pre-treated with pesticides known to harm bees and often lead to their deaths.

In fact, concentrations of neonicotinoid (neonic) pesticides -- which have been linked to recent declines in the region's been numbers -- were determined high enough in at least some of the plant samples tested to kill bees outright, assuming comparable concentrations in the flowers' pollen and nectar.

Furthermore, the study found 40 percent of plant samples that tested positive for pesticides contained two or more neonics.

The study is a follow-up to a first-of-its-kind pilot study released by Friends of the Earth in August, 2013, and includes an expanded list of samples and locations where plants were purchased, as undated data for assessing the distribution of neonic pesticides between flowers and the rest of the plant.

The new plant retail revelations comes days after President Obama called for a government-wide task force charged with devising a national plan to save populations of honey bees and other natural pollinators.

Bees and other pollinators, essential for the two-thirds of the food crops humans eat every day, are in decline in countries around the world.

A new meta-analysis of 800 peer-reviewed studies recently released by the Task Force on Systemic Pesticides, a group of global, independent scientists, strongly suggests neonics are a key factor in bee declines and harm beneficial organisms essential to functional ecosystems and food production, including soil microbes, butterflies, earthworms, reptiles, and birds.

The Task Force called for immediate regulatory action to restrict neonicotinoids.

"The high percentage of contaminated plants and their neonicotinoid concentrations suggest that this problem continues to be widespread," Lisa Archer, director of the food and technology program at Friends of the Earth-U.S., said in a news release. "Most gardeners have no idea that their gardens may be a source of harm to bees. We're calling on retailers to get neonicotinoid pesticides out of their plants and off their shelves as soon as possible. Until then, gardeners should buy organic plants to ensure the safety of bees."

More than half a million Americans have signed petitions demanding that Lowe's and Home Depot stop selling neonics and, in light of growing evidence of the pesticides' harm growing consumer concern, nearly a dozen nurseries, landscaping companies and retailers, have taken steps to eliminate bee harming pesticides from their garden plants and their stores, Friends of the Earth reports.

"A growing number of responsible retailers have decided to be part of the solution to the bee crisis and are taking bee-harming pesticides off their shelves," said Archer. "We urge Home Depot, Lowe's and other major retailers to join these leaders in making our backyards and communities safe havens for bees."

The latest market statistics indicate numerous plants sold in nurseries and garden stores across the U.S. and Canada are being pre-treated with systemic neonicotinoid insecticides, making them potentially toxic to pollinators, said Timothy Brown, co-author of the report, which was compiled by the Pesticide Research Institute.

"Unfortunately," he said, "these pesticides don't break down quickly, so these plants could be toxic to bees for years to come."