What was it all about?

Chestnut rot is a significant disease facing the Australian chestnut industry with a recent survey of south-eastern Australia finding symptoms in almost three-quarters of orchards. Chestnut rot, caused by the fungus Gnomoniopis smithogilvyi, causes brown lesions on the kernel of the chestnut fruit.

This project sought to improve understanding of disease management methods available to chestnut growers, and the relative cost and benefit of each.

The literature review showed that the key to reducing chestnut rot is to disrupt the infection process. It is critical to prevent fungal spores (known as ascospores) from spreading up to the flowering trees from infected burrs and twigs on the orchard floor.

There are various methods of preventing infection that growers can use…

• Cultural management methods include removing burrs and twigs from the orchard floor, mulching burrs using a wood chipper, growing thick ground covers in the lead up to, and during, the flowering period in December, as well as the application of mulches on top of dead burrs and other litter.
  
  
• Chemical methods include application of urea on burrs and twigs to enhance breakdown and alter the carbon/nitrogen ratio to reduce ascospore production, as well as spraying chestnut flowers with fungicides to prevent or reduce infection. The researchers caution that spraying flowers with fungicides has not yet been tested for any negative effects on pollination, fruit set or damage to trees. They also noted that fungicides can become ineffective over time.
  
  
• Biological methods include spraying burrs and twigs with bio-controls such as Trichoderma species and Gliocladium virens.

The cost and benefit of each method is presented in the final report. The researchers note that an individual grower’s decisions will depend on many factors including the size of the orchard, organic status of the orchard, the time a grower has to allocate to disease prevention and control, the financial capacity to purchase or hire machinery and obtain casual labour to remove dead chestnut material from the orchard floor.

The recommendation for growers is to use an integrated approach involving a combination of methods…

• Remove the majority of the burr and twig and branch material from the orchard floor
• Apply urea or another fungicide to the remaining dead material
• Grow a thick groundcover in the months leading up to and during flowering in December.