Investigations reveal no further spread of carnation fungus
No further detections of downy mildew (Peronospora dianthi), a minor disease affecting carnations, have been found
following surveys undertaken by the Ministry of Agriculture and Forestry (MAF).
George Gill, MAF’s technical adviser for plant pest management, reported that these results indicated the fungus may
have limited spread and that investigations were unable to reveal how the fungus got into the country.
“Downy mildew may have been present in New Zealand for some time, a possible source of entry is imported carnation seeds
or tissue culture. To find out we would need to trace the movements of all carnation plants on and off the affected
property prior to the detection in October and determine whether these plants were infected.
“Downy mildew has a very limited host range affecting only carnations, Sweet William, and pinks. MAF is satisfied that
no further action needs to be taken given that it is a minor pest that can be controlled by fungicide, also because of
the likelihood that it is already present in New Zealand,” he said.
During the investigation downy mildew was classified as an unwanted organism. This meant movement controls could be
imposed upon the affected property as a means to limit potential spread of the fungus, while MAF conducted further
investigations. This classification has now been removed and the grower is able to resume trade in carnations.
MAF’s investigation included surveying 14 properties growing ornamental carnations, an email survey to 40 commercial
growers around the country and discussions with the Australian Department of Agriculture, Fisheries and Forestry. Downy
mildew produces two spore types one of which is the short lived conidia found on the underside of leaves, the other more
resilient oospore can live several years in the soil and is produced internally in rotting leaf tissue. The fungus
flourishes in wet/humid conditions and is primarily spread by airborne conidia and/or water splash.
More information on downy mildew is available