This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Chestnut Rot posed a significant problem facing the Australian Chestnut industry at the time. Symptoms manifest as brown lesions on the kernel of the chestnut. The disease was often not visible externally, providing a challenge for growers and consumers alike.

The aims of the project were to survey New South Wales (NSW) and Victoria (VIC) for Chestnut Rot in 2008 and 2009; identify the organism associated with rotten chestnuts; clarify the infection process; determine the effectiveness of flotation grading as a post-harvest method; and provide recommendations to growers on how to manage the disease.

In 2008 Chestnut Rot incidence was up to 72 per cent, and in 2009 up to 35 per cent. The disease was present in all orchards in both years. All the sampled varieties were affected. There was a positive correlation between incidence and December rainfall of the previous year. Surveys of Flemington Markets, NSW showed incidence up to 10 per cent in 2008, and 9 per cent in 2009.

A fungus named Gnomoniopsis smithogilvyi sp. nov. was identified living on decaying chestnut burrs and branches, was isolated from diseased chestnut kernels, and was isolated as an endophyte from asymptomatic chestnut flowers, leaves and stems.

Airborne ascospores were captured in the laboratory on agar plates, and in a chestnut orchard, suggesting they are part of the infection process.

The effectiveness of post-harvest flotation grading of chestnuts was tested. Healthy chestnuts have previously been found to sink and rotten ones float. Five water temperature treatments were tested. Rotten chestnuts were found to sink in all temperature treatments, and healthy chestnuts floated in all except 70°C, indicating the method should be used with caution.

Orchard sanitation was key to Chestnut Rot management. Burr removal or the placement of a layer of organic mulch over top of burrs are options. Growing a range of varieties was also recommended to spread out the flowering times and reduce the risk of floral infection.

Surveying South Australia, Western Australia and Tasmania as well as internationally needs to be completed to further determine the distribution of the disease. Burr removal and investigating mulches was an important area of future research. The effectiveness of biological control agents such as Trichoderma sprayed on infected burrs should also be investigated.