White root rot
White root rot is caused by the fungus Rosellinia necatrix. It's highly polyphagous, infecting:
- woody hosts
- herbaceous plants
It forms mycelial webs and strands close to roots and bark is invaded, often with fan-like mycelium growth.
The fungus rots root systems and produces phytotoxins that are transported in the sap, leading to a decline in the vigour of the entire plant.
Symptoms of white root rot
The following symptoms can indicate white root rot:
- 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.
- Mycelial mats, ranging in colour from white to greyish, might be present under the bark at the base of trunks (Figure 1).
- As the disease progresses, the infected tissue becomes rotten.
- Trees develop a generally unthrifty appearance with leaf yellowing, halted root growth, wilt, small leaves, early leaf fall and small, shrivelled fruit (Figure 2).
- Infected trees will eventually die. Mature apple trees can die over 12 seasons, while newly planted trees can die in a few months (Figures 2 and 3).
The major host plants are:
- Actinidia chinensis
- Boehmeria nivea
- Camellia sinensis
- Citrus spp.
- Cydonia oblonga
- Cynara scolymus
- Diospyros spp.
- Eucalyptus spp.
- Eriobotrya japonica
- Ficus carica
- Fragaria vesca
- Malus domestica
- Olea europaea subsp. europaea
- Populus spp.
- Prunus spp.
- Pyrus spp.
- Vitis vinifera
White root rot in Australia
It was first recorded in Queensland's Granite Belt on apples in 1979. The fungus hasn't been recorded in Victoria to date.
Limited information is available on how the disease is distributed across Australia and which hosts are affected.
Anecdotally, grapevines and stone fruit growing in the Granite Belt in Queensland have no symptoms of disease, nor have there been any detections of the fungus from these crops. But both have been recorded as being hosts of this disease overseas.
White root rot in New Zealand
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).
Reporting an unusual pest or disease of plants or honey bees
Report any unusual plant pest or disease immediately using our online reporting system. Early reporting increases the chance of effective control and eradication. Please take good quality photos of the pests or damage to include in your report where possible.
Alternatively, you can call the Exotic plant pest hotline on 1800 084 881.Report online
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.
Images © The State of Queensland 2020
Figures 1, 2 and 3 courtesy of The State of Queensland 2020.