What was it all about?

During 2023, this investment collated all the available scientific literature on chestnut nut rot, in particular biology, control and management, to underpin the development of a research and management plan for the Australian chestnut industry to combat the disease.

Nut rot of chestnuts is an emerging disease becoming of worldwide importance. In Australia up to 70 per cent of chestnuts may be affected, while in Europe losses may be as high as 90 per cent. The disease is mainly expressed after harvest, and it is cryptic, as healthy-looking nuts on the surface are rotten internally. It is a disease of great economic importance as infected nuts cannot be consumed, is not easily detected and hence reduces consumer confidence when unknowingly purchasing infected chestnuts. 

The available literature confirms that the pathogen, Gnomoniopsis smithogilvyi, is also an endophyte that can be found in symptomless chestnut tissue. However, the triggers allowing the fungus to “switch” from an endophyte to a pathogen are still unclear.

A modelling study identified high temperatures and wind in the months prior to harvesting as associated with disease development but narrowing this down to specific months/periods would be helpful in developing a disease forecast model.

Various options for disease control have been investigated, both biocontrol and chemical. Biocontrol options seems largely ineffective as a control option in orchards or as a post-harvest option, while chemical options may provide some, but perhaps not adequate protection. Their efficacy under Australian conditions needs further investigation. The effect of chemical applications on the endophyte community is unexplored and may actually be detrimental to chestnut health in the long term.

Reducing the number of diseased chestnuts in storage and on the market, still poses challenges even though a number of disease-reducing options have been investigated, mostly with limited success. Removing plant debris and floating chestnuts will assist in getting rid of the worst affected chestnuts, but not all. Options such as a hot water treatment (curatura) seems largely ineffective, while an ozone treatment may offer some protection, although it is unclear how long that protection lasts.

An integrated management strategy is suggested by removing litter on the orchard floor to reduce inoculum, combined with possible chemical applications.

Further investigating the factors associated with infection will help in establishing a disease forecast model to inform growers when chemical applications will be most effective based on environmental conditions.