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Ongoing project

Australian Citrus Postharvest Science Program (CT15010)

Key research provider: NSW Department of Primary Industries

What’s it all about?

The development of rots and decay (such as green mould) after harvest can be a serious problem for growers and packers, particularly in fruit for export markets where produce is stored and transported over many weeks.

The Australian Citrus Postharvest Science Program is working to develop best practices to manage current fungicides and sanitisers to control decay, and to ensure Australian citrus remains clean and green with ultra-low residues. The project is continuing to review and extend the best ways to control post-harvest decay and improve the quality of Australian citrus.

The project team has been working on the following activities:

Fungicide resistance survey

Surveys from different packinghouses around Australia for the 2017 season have been completed, reported back to individual growers/packers and key outcomes communicated to industry. This process has been very successful with individual packers making changes to their postharvest practices to improve sanitation and reduce the risk of developing tolerance to postharvest fungicides. The project is working with other stakeholders to extend these outcomes.

Review of low dose irradiation treatment

While cold treatment is a well-established and useful market access treatment for the Australian citrus industry, it is costly, can cause chilling injury and can take up to 18 days. As a potential alternative, a review of low dose irradiation as a potential market access treatment has been completed with the project team making recommendations about its potential use and future research priorities. The outcomes of this literature review are with industry and demonstrate the potential applications of this technique, especially for citrus types susceptible to chilling injury.

In summary, the review highlighted:

  • Postharvest low dose irradiation is an accepted safe phytosanitary treatment for some key export markets
  • Irradiation overcomes any issues of chilling injury with cold treatment for export
  • There are few consistent negative effects of irradiation on final citrus fruit quality following treatment and storage.

Dithiocarbamates

Dithiocarbamates are an important group of fungicides used to control black spot and mites, but residue levels can be a problem with overseas markets. The team carried out a study assessing how well various kinds of post-harvest washing worked at reducing dithiocarbamates on lemons and found that all worked to varying extents. Each could be part of the answer.

Postharvest pathology experiments

The team also released results from postharvest pathology experiments that were conducted to assess a range of conventional and non-conventional decay control measures. They found that a newly registered post-harvest fungicide was effective if applied quickly after harvest, and showed how well potential non-chemical postharvest treatments can minimise decay during storage. None of these treatments were as effective as synthetic fungicides, but there is potential to apply combination treatments. More work is continuing in this area.

Sanitisation of packinghouses

Experimental work has confirmed that sanitation of packinghouses can reduce fruit decay. A comparison of the 2018 results from the 2017 season showed there had been some reductions in the levels of total decay causing spores in the packinghouses and cool rooms in the 2018 season. Fewer decay-causing spores reduces decay and reduces the risk of developing resistance to current treatments. A new fee-for-service sanitation and fungicide resistance service is being developed between NSW DPI and Citrus Australia to service the needs of the Australian citrus industry.

Industry communications

The team continues to prioritise communicating their findings. Two short videos were developed on the postharvest fungicide resistance survey, and on degreening.  They also presented to growers and packers at the 2019 Citrus Technical Forum, and the pre-conference tour, along with poster presentations, and provided articles for inclusion in Australian Citrus News, among other initiatives.

ACT NOW

Watch the short videos from the project team on the Do’s and Don’ts of degreening or on the postharvest fungicide resistance survey.

For a more in depth understanding of some of the research carried out, you can download the following reports:

The project has been facilitating the adoption of new and existing post-harvest approaches through face-to-face interactions across key growing regions (such as the Riverina) as well as through industry articles in Australian Citrus News, with regular updates and articles provided in the publication.

Project activities have recently focused on the assessment of fungicide resistance across Australian citrus packing sheds. A nationwide survey of packing shed hygiene and resistance to post-harvest fungicides was conducted during the 2017 growing season. The results of this survey have shown there is room to improve sanitation practices and the use of fungicides within some packing lines. These results will be discussed with industry at upcoming workshops and post-harvest forums around Australia.

ACT NOW

The Australian Mandarin Production Manual was released in February 2018. You can request a copy through Citrus Australia, or by contacting NSW DPI at dareton.office@dpi.nsw.gov.au or on (03) 5019 8400.

As (at the time of writing) picking and packing is well underway across Australia, NSW DPI is regularly in the field, working closely with a range of commercial packing sheds. Ultimately, the aim is to get the best out of post-harvest fungicide treatments for the citrus industry while maintaining high quality and low residues, as expected from Australian citrus in the market place.

As reported in last Hortlink, the program is also currently working to contribute to a new Australian Mandarin Production Manual, which is expected to be released to industry shortly. Work is also continuing to survey post-harvest fungicide resistance in all citrus producing states. This will progress toward improving awareness of fungicides and maintaining their efficacy.