A nature reserve in mid Wales is banning all visitors from picking wild mushrooms because it says some species are in decline.
Daniel Butler has been a mushroom guide for nine years
The Elan Valley Trust, responsible for flora and fauna on the Elan Estate, said any lesser restrictions would be impossible to police.
The estate's head ranger said some people were "cashing in" by selling car boot loads of the mushrooms.
But it is unclear how the trust intends to prevent mushroom picking.
Chairman John Evans defended the blanket ban at the Elan Estate.
"Our feeling is that if you permit some people to take some fungi, some of the time, in some places, that it is impossible to police that," he said.
"Applying a precautionary principle, we think it is wiser to have a total prohibition on the removal of any fungi on the estate.
"To study fungi, we do not believe it is necessary to remove the fungi."
To illustrate the problems faced by the trust, Mr Evans said a rare bog orchid had been picked to extinction on the estate.
Head ranger Peter Jennings said there were no plans to erect warning signs on the 70 square mile (181.3 square kms), 42,000-acre (16,997 hectares) estate which is in the counties of Powys and Ceredigion.
He claimed that some people were "cashing in" on the mushrooms as well.
He said: "We have had people from eastern Europe picking whole (car) boot loads for commercial purposes.
"I have been here 20 years and in my time numbers have declined and some species have disappeared from some sites, and it's no coincidence it's the ones that sell for the most money."
However, Daniel Butler, who has carried out guided fungi tours of the estate, questioned the ban.
"I have been doing this for nine years without any problems, and there is no scientific evidence that I'm causing any damage whatsoever by picking mushrooms," he said.
Asked why he had to pick the mushrooms instead of just looking at them, he added: "They are fantastically edible, but some are only about an inch off the ground and difficult to see without picking.
"I'm not commercially exploiting the valley, but I want to open people's eyes to mushrooms."
Mr Butler claimed that his fungi tours generated about £25,000 for the local economy, and this year 84 people are expected to take part.
He said there were about 10,000 species of mushroom in Britain and about 1,000 were found on the estate.