Some studies have found neonicotinoids harm bees but science is split over whether using the chemicals on plants harms pollinators. The study could call into question the use of the RHS "Perfect for Pollinators" logo, which does not stipulate that plants bearing the badge should be neonicotinoid-free.
Professor Dave Goulson is running an £8,000 Walacea crowdfunded study to sample 100 plants from 10 garden centres to test for the presence of the insecticides. But HTA horticulture head Raoul Curtis-Machin said: "We live in a world where science doesn't necessarily govern consumer habits if consumer habits run by emotions. They vote with their wallets."
Curtis-Machin has met Goulson and hoped to run experiments to mirror the University of Sussex scientist's study. But Curtis-Machin said: "He'd started work so it was too late to do our mirror study in time. We agreed we'd look at his results and make up our mind after that. The last thing we want to do is for the report to stop people buying plants. He agreed it is more important to have flowering plants than not.
"We wanted to do our own version to broaden the knowledge because what he's doing is not quite as vigorous and far-reaching as we'd like. We know he's planning to measure in leaves but we need to know in nectar/pollen whether bees are being affected. We want to support learning but need sure scientific research."
Goulson said: "The study is going well. We should have results finalised by November. We are analysing leaves, pollen and nectar separately. I'm afraid that I can't give any sneak previews." Asked whether a report saying neonicotinoids are in nursery plants could stop people buying plants, he said: "Yes, that certainly could be a concern."
Curtis-Machin said nurseries and garden centres are "concerned" but none have yet acted on the issue. "Ramping up research on vine weevils" could be a way forward to stopping neonicotinoid use, he suggested.
In January 2016, US grower Bell Nurseries said it had stopped using neonicotinoids under pressure from retailer Home Depot. US garden retailers appear to be selling fewer ornamental plants with traces of neonicotinoids in them, according to a new Gardeners Beware report.
Some 23 per cent of plants (14 out of 60) from stores and nurseries tested by environmental activists contained pesticides at levels that could be harmful to bees. Two previous reports, in 2013 and 2014, revealed that more than half of the samples contained neonicotinoid traces.
"Our data indicates that compared to two years ago, fewer nurseries and garden stores are selling plants pretreated with systemic neonicotinoid insecticides," said Susan Kegley, a chemist at the Pesticide Research Institute and lead author of the report by the institute and Friends of the Earth. The study was of plants bought at Home Depot, Lowe's, Ace Hardware, True Value and Walmart. The 2016 report suggested grower production methods have resulted in reduced use of neonicotinoids in common garden plants overall.
Large retailers including Home Depot and Lowe's have made commitments to phase out use of these pesticides. Ace Hardware, True Value and Walmart have not yet made similar commitments.
A 2016 YouGov poll released in conjunction with the report found that 67 per cent of Americans feel more positively about Home Depot and 66 per cent feel more positively about Lowe's because of their formal commitments to eliminate neonicotinoids. Following the survey, half of respondents said they are more likely to shop at Home Depot (50 per cent) and Lowe's (51 per cent) because of the commitment. More than a third (39 per cent) said they would feel more negatively about a retailer that has not formally committed to eliminate systemic neonicotinoid insecticides. Pressure group 38 Degrees launched an unsuccessful UK campaign on the issue in 2015.