Bedding busy Lizzies are set to be in short supply for a second year running.
The disease, which prompted T&M to pull Impatiens walleriana from its catalogue in 2012, quickly wipes out plants during warm, damp weather.
The decision to stop supplying bedding busy lizzies last year cost T&M around £1million in lost sales.
T&M Young Plants managing director Paul Hansord told AG the mildew has now spread across Europe and has even struck in the USA, too.
“I do not want our customers wasting time [growing them], only to be disappointed,” explained Paul. “This is a long-term decision.”
Paul said customers turned to begonias instead last year, which made up 25 per cent of lost busy Lizzie sales.
Lilies and dahlias also did well. But sales of New Guinea busy Lizzies, which do not succumb to mildew, were not as promising as T&M hoped.
Retail giant B&Q has also decided to pull the plug on busy Lizzies.
A spokeswoman said: “We’re not going to reintroduce them this year. There is still a risk of disease. We are working with growers to provide alternatives for the public.”
But Suttons, which offered Impatiens walleriana last year, will continue to supply seeds and young plants.
A spokeswoman said: “Sales of young plants dropped heavily, up to 60 per cent, when the mildew problem became known. However, a bit of a recovery is taking place and sales are now rising.”
Mr Fothergill’s said it would also be offering Impatiens walleriana this year.
A spokesman said: “They still sell. However, since the mildew problem, sales are around half of what they used to be.
“Begonia semperflorens [plants] have taken their place, with sales are up by around 20 to 25 per cent.
“New Guinea impatiens (Impatiens hawkeri) increased by 25 per cent, as this species is not susceptible to mildew problems.”