Scientists developing genetically modified wheat are asking campaigners not to ruin their experimental plots, but come in for a chat instead.
The trial at Rothamsted Research in Harpenden, Herts, uses wheat modified to deter aphids, an insect pest.
The protest group Take the Flour Back has vowed to “decontaminate” the site unless the research is halted.
The scientists say the GM plants could benefit the environment as they will reduce pesticide use.
“We appeal to you as environmentalists,” they write in an open letter.
“Our GM wheat could, for future generations, substantially reduce the use of agricultural chemicals.”
But the campaigners say the GM trial presents “a clear risk to British farming”.
They argue that genes from the modified strain could spread into neighbouring fields, and that there has been no evaluation of whether foods made from the GM variety would be safe to eat.
They are planning a day of action on 27 May, trailed on their website as “a nice day out in the country, with picnics, music… and a decontamination”.
Rothamsted’s wheat contains genes that have been synthesised in the laboratory – an approach that is becoming more commonplace than transferring genes from other organisms, as technology develops.
The gene will produce a pheromone called E-beta-farnesene that is normally emitted by aphids when they are threatened by something.
When aphids smell it, they fly away.
“Also, the natural enemies of aphids – ladybirds, lacewings and a particular parasitic wasp – when they smell this smell, they’re attracted,” said Prof Huw Junes, one of the study team who signed the open letter.
“So it’s potentially got an advantage in the UK and other western nations because it’ll prevent the need to spray insecticide – and [in the developing world where] farmers don’t have access to insecticide, they’d have that packaged up in the seed.”
However Lucy Harrap from Take the Flour Back doubted the crop’s environmental credentials.