Plant Heritage Collection holder Carrie Thomas of Touchwood Plants who holds the National Plant Collections of Aquilega is warning that downy mildew is spreading nationwide.
HW reported on 10 February that Thomas' collection had been decimated by the disease. She now says the disease has spread to large public gardens in the south east on plants from commercial nurseries.
She said: "This disease is sweeping the south of England. Think Ebola or AIDS - the plants have no resistance."
She has been in contact with plant pathologists Geoff Denton at the RHS and Sara Redstone at Kew about the issue. Since February German pathologist Prof. Marco Thines has been in touch with Thomas and the RHS and is writing a paper on the issue.
Nursery consultant John Adlam said the disease could be peronospora ranunculi and if it is then there is a range of control products available. He said: "The Hebe growers had a similar situation 10 years ago when hebe downy mildew came to the forefront. They found that through a combination of measures keeping the foliage dry by basal irrigation and good air movement through the crop with a programme of control products they were able to keep the disease at bay. We anticipate that Aquilega downy mildew will be controlled by a similar approach."
He added that because awareness of the disease had risen, it was being found more. Adlam said he does not think nurseries selling diseased plants is the sole means of spread of this disease: "I have seen the disease on plants that were supplied over a year ago.Many of these diseases can be spread by animals, birds and even bees."
Know the signs - Control the disease
HDC knowledge transfer manager Wayne Brough said HDC factsheet 09/14 'Control of downy mildew diseases on hardy nursery stock and perennial herbaceous plants' covers the appropriate cultural and chemical control measures.
The RHS said it has identified a growing number of cases of Aquilegia downy mildew in public and private gardens, as well as nurseries. In April it intercepted a batch of infected Aquilegia plants before they reached the Plant Centre at Wisley. The plants were returned to the supplier.
The RHS said there are no control and management methods available for the home gardener, but the prompt removal of infected plants is currently advised. See www.rhs.org.uk/advice/profile?PID=866
Kew has had one case in the gardens and two suspected cases. Kew said: "We will cooperate with all parties to minimise Aquilegia Downy Mildew's impact."