New Guinea types of Impatiens as well as Begonia, Verbena and Petunia are some of the flowers suggested as substitutes for I. walleriana, which currently makes up 40 per cent of the bedding-plant market.
Simon Crawford, speaking as an independent consultant for his own business Flowers by Design, said: "Breeding resistant varieties with I. walleriana is not an option for at least three years, so while these long-term projects are going on we need other ways around it.
"If we have another wet summer it could decimate (busy Lizzie) plants with resting spores, so should we offer more New Guineas as alternatives?"
He added: "While there are already good seed- and cutting-raised varieties, more work is needed on New Guinea varieties. We could look to begonias, verbenas and petunias - which are increasingly rain-tolerant - or pansies, which now last throughout the summer."
Crawford is also concerned about the impact of companies not admitting they have been affected.
"We can't deny it's a problem and bury our heads in the sand. Obviously the disease is a sensitive issue from a supply point of view. But growers and suppliers need to be more transparent and try to work together. It's terrific that we have got the HDC-funded project by Dr Martin McPherson at the Stockbridge Technology Centre as we need answers very quickly."
Cotswold Wildlife Park head gardener Tim Miles said: "We need to look at what is the way forward. We've used Impatiens extensively in the past at Cotswold Wildlife Park. What's going to replace it?"
He also said the RHS may need to update where it stands on the issue and send out further guidance to its membership.
The RHS last reported on the issue in August. It recommended destroying diseased plant material and not replanting Impatiens in the same position the following year because downy mildew spores may be lurking in the soil.
The HDC will hold a "disease day" early next year, during which up-to-date recommendations on prevention and control of Impatiens downy mildew will be presented.