White root rot
White root rot caused by the fungus Rosellinia necatrix was first recorded in Queensland's Granite Belt on apples in 1979. The fungus has not been recorded in Victoria to date.
Symptoms and management
R. necatrix forms mycelial webs and strands (Liberato 2007). The pathogen causes root and collar rot of trees, leading to a decline in the vigour of the entire plant and a general rot of the underground parts of fleshy plants.
In fruit trees, the base of the trunk at soil level can show signs of a dark, wet rot, especially if kept moist by weeds or wet weather.
As the disease progresses, the infected tissue becomes rotten. Trees develop a generally unthrifty appearance with leaf yellowing, cessation of root growth, small leaves, premature leaf fall and small, shrivelled fruit. Infected trees will eventually die.
Mature apple trees can die over 12 seasons, while newly planted trees can die in a few months.
In New Zealand, infected mature apple trees typically decline slowly, with yellowing foliage and poor branch growth. Occasionally the trees collapse and die rapidly in midsummer. The disease is favoured by cool, moist soils and has been observed in stone fruit, olive and persimmon orchards in New Zealand. Once established in orchard soils, the disease is almost impossible to control and will kill any new trees planted in that soil (Dance 2007).
According to the Crop Protection Compendium (2005), the major host plants are: Actinidia chinensis, Begonia,, Boehmeria nivea, Camellia sinensis, Citrus spp., Cyclamen, Cydonia oblonga, Cynara scolymus, Dianthus, Diospyros spp., Eucalyptus spp., Eriobotrya japonica, Ficus carica, Fragaria vesca, Jasminum, Malus domestica, Morus, Narcissus, Olea europaea subsp. europaea, Paeonia, Populus spp., Prunus spp., Pyrus spp., Rosa, Viola, and Vitis vinifera.
Limited information is available on how the disease is distributed across Australia and which hosts are affected.
Anecdotally, grapevines and stonefruit growing in the Granite Belt in Queensland have no symptoms of disease nor have there been any detections of the fungus from these crops. Grapevines and stonefruit have been recorded as being hosts of this disease overseas.
Crop Protection Compendium 2005 Edition. Rosellinia necatrix (Dematophora root rot). CAB International, Wallingford, UK.
Dance, M. 2007. Diagnostic component of Report for AgFirst Consultants HB Ltd.
Liberato JR (2007) White root rot (Rosellinia necatrix) Pest and Diseases Image Library.
To report suspected exotic or unusual pests or diseases, call the EXOTIC PLANT PEST HOTLINE 1800 084 881