Hortex Garden Products owner Pauline Hare said she was selling off the last of her stocks: "The old-fashioned gardeners want these things, the tried-and-tested products. Sodium chlorate is the latest thing that is going to go.
"They are not being replaced by anything. We've had stocks to get rid of and have had to throw some products away. There will be nothing soon for the ordinary gardener."
A Chemicals Regulation Directorate representative said it would enforce the regulations if it was told who was selling the product.
Derris can be stored and used until 10 October.