Pg. 80-83 The effect of pre-harvest application of chemicals on post-harvest decay development on litchis

The control of post-harvest diseases on litchi by means of pre-harvest application of fungicides is not a common practice in South Africa. Currently there are no fungicides registered in South Africa for pre-harvest application on litchi. The aim of this trial was to determine the effect of pre-harvest fungicide application on the control of post-harvest diseases. Three trial sites were sprayed and five fungicides were evaluated. At one trial site Phytex 200 SL reduced post-harvest decay, and copper-based fungicides had some effect. In general poor control of litchi postharvest diseases was obtained at the other two trial sites probably due to higher disease incidence related to climatic factors. Prochloraz post-harvest treatment effectively reduced decay, especially if combined with effective pre-harvest programs.

Summary:

• Post-harvest disease control on litchis via pre-harvest fungicide application is uncommon in South Africa, with no registered fungicides for pre-harvest litchi treatment locally.
• The study aimed to evaluate the effect of pre-harvest fungicide sprays on post-harvest disease control at three trial sites using five different fungicides.
• One trial site showed that the fungicide Phytex 200 SL significantly reduced post-harvest decay; copper-based fungicides demonstrated some effect, but other fungicides generally showed poor control.
• Poor post-harvest disease control at two sites was likely influenced by higher disease pressure related to climatic differences.
• Post-harvest treatment with prochloraz markedly reduced decay, especially when combined with effective pre-harvest fungicide programs.
• Pre-harvest programs can partially reduce the incidence of post-harvest decay but generally do not give fully acceptable control when used alone.
• Some fungicides may cause removal of natural antagonists or have slight phytotoxicity which could explain inconsistent results.
• The study highlighted the need for further research to identify effective fungicides for litchis, establish optimum application timing, and evaluate residue safety.
• Storage conditions at ambient temperatures were harsh and led to high decay rates despite treatments; optimal storage for export is 1-3°C with evaluation after cold storage.
• The best post-harvest decay control was achieved by combining pre-harvest Phytex application with post-harvest prochloraz dipping, yielding up to 91.7% disease-free fruit.
• Other fungicides like Copper Count-N and Copstar also showed reasonable efficacy in some trials.
• The study recommends further investigation of integrated pre- and post-harvest chemical control strategies to manage litchi post-harvest decay effectively.