Thousands of gardeners, wagons in tow, lined up at the State Fair grandstand this weekend for the Friends School plant sale as they jockeyed for position at the official start of Minnesota’s annual spring planting frenzy.

They were also standing at the forefront of what has been a swift and surprisingly successful consumer revolt against a class of pesticides widely blamed for the decline in honeybees and other pollinators. Thanks to pressure from backyard gardeners like these, every one of the 535,000 petunias, roses, tomatoes, rosemary, clematis and other plants that left the grandstand — plus those at many other garden centers in Minnesota and around the country — today are largely free of neonicotinoid pesticides.

This year an industrywide survey found that 60 percent to 75 percent of growers nationally no longer use that class of insecticide to protect their plants, a remarkable transformation that has swept the industry in just a few years.

Even some of the chemical companies are getting the message: Scott’s Ortho, the nation’s largest manufacturer of backyard chemical products, announced this spring that it would no longer sell neonicotinoid insecticides for homeowners.

“People should realize they were listened to,” said Vera Krischik, a toxicologist at the University of Minnesota.

Neonicotinoids are the most widely used pesticide in the world — particularly in agriculture, and until recently in the commercial plant world. They were rapidly adopted by both industries because they are easy to use and much safer for people and mammals than the pesticides that preceded them.

But since their widespread adoption in the 2000s, they have sparked a global debate about their role in the ongoing decline in honeybees and other insects.

Instead of being sprayed to stop an infestation of bugs, they are applied as a preventive coating to seeds or as a liquid; they are absorbed by the plant as it grows, making the whole plant toxic. That might be fine for pests like aphids and white flies, but not for the bees and butterflies that bring joy and, quite literally, life to a garden.

“Without insects, there would be no flowers,” Krischik said.

The pesticide industry says that if used correctly, the insecticides don’t harm pollinators because the toxins become diluted as the plant grows. But an ever larger array of scientific studies has found that they may play a major role because they are harmful at the “sublethal” doses that insects encounter in gardens and farm fields.

Gardeners, however, have not waited for the definitive scientific answer.

In 2013 the Friends School was among the first in Minnesota to vote with its checkbook. The volunteers, who have run the fundraiser now for 27 years, started asking questions about how growers grow their plants. Most already came from organic growers that didn’t use neonicotinoids anyway. But about a fifth of the supply — including roses, bulbs, and bare root plants — were grown with the systemic insecticides.

The Friends School refused to buy them.

“Everything we’ve done as a society is bad for bees,” said Victoria Erhart, a volunteer who has helped run the Friends School plant sale for many years. “It seemed like the ‘do no harm’ was pretty strong.”

Their decision had overwhelming support among customers, organizers said.

“We have to get rid of them,” said Joan Newman, a master gardener from Stillwater who waited in line Thursday evening for the plant sale to open. “I think the research is there.”

‘The public let us know’

Bachman’s is one of several nurseries and garden centers that began shifting its growing practices that year as well. It no longer uses neonicotinoids for its own plants and is working with other growers that supply its garden centers to reduce or eliminate neonicotinoid use.

“The public let our industry … know loud and clear that they are concerned,” said John Daniels, Bachman’s vice president of production.

Since then, some of the nation’s big box retailers have also succumbed to the pressure from conservation groups and customers. Home Depot, for example, says that 80 percent of the plants it sells are now grown without those pesticides, and the phaseout will be complete by 2018 unless there is “undisputed” scientific proof that they have no lethal or sublethal effect on pollinators.

This year, in its annual state of the industry survey, Greenhouse Grower magazine reported that 73 percent of growers serving home improvement chains and 58 percent serving independent garden centers said they will drop the insecticides by 2016.

“It’s been one of the fastest-changing things that I’ve been a part of,” said Daniels.

But it hasn’t been easy.

Karen O’Connor, co-owner of Mother Earth Gardens in Minneapolis, has always specialized in organic products. But when she started quizzing her nonorganic growers about how they grew plants, and how their suppliers grew plants, she found neonicotinoids were used up and down the chain.

“The horticulture industry is complicated,” she said. For instance, “Ornamental tree and shrub growers are making a five- to 15-year commitment in a plant. You can see why they are not inclined to say they are not using them.”

Picky customers, too, sometimes balk at plants that come with insects or the damage they inflict, said Heidi Wollaeger, an educator at the Michigan State Extension Service who does customer research for growers. Some “do indeed want it all: insect-free, perfect plants, that will be safe for bees,” she said.

That’s forced growers to go back to the drawing board, or at least to insecticides that may not be as risky for bees, but are more difficult for the industry.

“It’s tough choices,” said Daniels. “That means we are using more chemicals more often. And the neonics were safer to humans as well.”

Price matters, too

Just how deeply the anti-neonicotinoid sentiment runs in the hearts of consumers remains unclear. Retailers say they responded to the small but most passionate group of gardeners, who also tended to be the most well-informed about the issue.

Wollaeger said the vast majority of customers are familiar with the term “bee friendly” but are mixed on whether it means good for bees or attractive to bees. And whether or not a plant is grown with “eco-friendly” practices is still less important to them than the species of plant and its price, she said.

And that was true for some at the Friends plant sale as well.

Mary Bankovics, a gardener from Mounds View, said she tries to ask plant sellers about their growing practices and use of neonicotinoids. But sometimes she forgets, she said as she headed out with a full wagon, especially when “a pretty flower will just turn my head.”