What was it all about?

This project which ran from 2013 to 2016, addressed fungal disease control in the citrus industry with the goals of minimising the financial impact of fungal diseases, and overcoming market-access barriers related to them.

It had a specific focus on citrus black spot (CBS) and emperor brown spot (EBS), and included the investigation of…

• Fungal disease control protocols
• Improved fungicide options
• The use of disease-resistant varieties to reduce the use of fungicides.

During its life, the project…

• Evaluated fungicides in the field for efficacy against CBS and EBS. There were 11 alternate fungicides screened over four seasons. Four promising fungicides were identified with registration potential for EBS (SDHI fungicides fluxapyroxad and boscalid, and multisite fungicides captan and dithianon), which were up to twice as effective as standard mancozeb. There was one promising fungicide identified for both CBS, also effective for EBS (multisite fungicide dithianon). Subsequently, efficacy and residue data was provided to support the application for a new minor use permit for captan, for the control of EBS in mandarins. Permit PER82043 was issued by the Australian Pesticides and Veterinary Medicines Authority in October 2016. The rate and use pattern of the permit were determined by this project, with the use pattern focussed on a major gap that occurs in the existing fungicide use patterns during autumn/winter, when EBS is typically most damaging.
  
  
• Evaluated the duration of fungicide efficacy in the field. The researchers generated ‘efficacy decline curves’ for commercially used fungicides and promising new fungicides, showing rapid decline can occur within as little as 11 days after application, but can persist for up to 30 or so days. The researchers note that the potentially very short time frames for high-level protection in the field were surprising, as it is anecdotally accepted that four-to-six-week spray intervals may be sufficient. They recommend a need for a shift in fungicide application practices towards targeting forecast infection events, as opposed to calendar-based applications.
  
  
• Conducted preliminary evaluations of fungicide reside profiles and post-harvest reside removal treatments. The reside profiles of any new fungicides – and the potential for post-harvest reside removal – need to be determined in order the maximise the likelihood of registration of new fungicides. Residue data supported favourable residue levels in fruit treated with promising new fungicides, and indicated up to five-fold reductions in fruit residues from standard packing line procedures.
  
  
• Was involved in EBS resistance breeding, providing support to the industry’s breeding program to produce an additional 12,750 resistant mandarin hybrids during the project’s life. The researchers note that resistance to EBS is under simple genetic control and is readily achievable through hybridisation breeding followed by screening of hybrids for resistance.
  
  
• Undertook laboratory screening to test the sensitivity of CBS to commercial post-harvest fungicides. The researchers note that a major step forward for overcoming trade barriers due to CBS would be the development of a post-harvest fungicide, but current commercial treatments do not offer reliable control. This research supported the idea that this poor post-harvest fungicide efficacy against CBS is actually due to poor fungus/fungicide contact, opening the door for further investigation and protocols.