New fungus found on carnations

19 November 2002

A new fungus specific to carnations was discovered on a North Island property in October.

Following routine procedures for detection for new organisms, the Ministry of Agriculture and Forestry (MAF) is investigating to find out how far the downy mildew (Peronospora dianthi) has spread and how it got into the country.

George Gill, MAF's technical adviser for plant pest management, has contacted as many commercial growers to notify them of this new disease and has asked them to notify MAF if they suspect the disease in their carnations, pinks or sweet William. Severely infected plants have stunted growth with a deceptive profusion of shoots at the base of the plant giving a bushy appearance. The disease shows up under moist conditions.

The fungus 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 humid conditions and is primarily spread by airborne condida or water splash.

"Downy mildew is an unwanted organism in New Zealand and has the potential to damage susceptible varieties if environmental conditions are favourable."

"Notifications by growers will help MAF determine whether the disease occurs elsewhere. We are particularly interested in ornamental carnations that may be afflicted," he says.

MAF provides a free identification for any specimens sent to the National Pest Plant Laboratory in either Auckland or Lincoln. For further information call 0800 809 966

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