The forthcoming Horticultural Development Company (HDC) report on downy mildew control on protected ornamentals and an updated leaflet with a list of new controls will offer hope in combating the disease, ADAS consultant Dr Tim O'Neill has advised.
He told the British Protected Ornamentals Association conference (22 January): "The good news is since we started this HDC project several products have been put forward to the Chemicals Regulation Directorate for off-label or extension of authorisation for minor uses approval. There's quite a nice range for downy mildew but whether that is sufficient for impatiens we'll see in due course."
He said to alternate fungicide groups because of resistance worries and to consider phosphites as protectants.
Ball Horticultural Company plant pathologist Colleen Warfield said impatiens downy mildew hit the USA as early as 2011. New Guinea impatiens has proved to be an inadequate replacement to consumers, as have begonias, but vinca has showed more promise. Warfield added that impatiens walleriana sales are expected to rise in 2014 despite downy mildew "because people think the problem has gone away, but it hasn't".
Bio-pesticides - Championed at conference
ADAS consultant Tim O'Neill and Biorationale director Roma Gwynn made the case for bio-pesticides at the conference.
Because of Sustainable Use Directive rules, growers are "to only use conventional pesticides when all other options have been considered", they said.
This means that bio-pesticides must be used in preference to chemicals to ensure compliance with sustainable urban drainage, if the alternatives are effective.
However, there are only about eight bio-fungicides and bio-pesticides registered for use and they have limited action.