Pg. 63-65 Control of post-harvest diseases of litchi fruit with different fungicides and fungicide mixtures applied as dip treatments

Decay and browning of the pericarp is major factors affecting storage life and marketability of litchi fruit. Fumigation sulphur is the only chemical registered to control post-harvest decay on litchi fruit in South Africa. The increasing concern of consumers regarding sulphur residues in fruit and relatively high decay levels in spite of treatment, warrant investigation to find alternative measures to reduce decay of litchi fruit. Several fungicides and mixtures were evaluated as dip treatments in ambient or heated solutions for their ability to reduce post-harvest decay of litchi fruit. In this trial, heated solutions performed significantly better than solutions at ambient temperature when fungicides were evaluated alone, except for fludioxonil. Slightly better results were obtained for fungicide mixtures used at ambient temperature
compared to similar mixtures when heated. The best control of post-harvest decay after simulated export for 28 days and storage of fruit for 7 days at ambient temperature was obtained with prochloraz and fludioxonil mixtures. This was followed by fludioxonil applied alone at 300 ppm. Prochloraz and guazatine mixtures also gave significant reduction of post-harvest decay compared to the untreated control, guazatine and prochloraz applied alone. Concentrations of especially fludioxonil, alone and as part of a mixture, must still be optimised for treatment of litchi fruit.

Summary:

• Post-harvest decay and pericarp browning significantly affect the storage life and marketability of litchi fruit.
• Sulfur dioxide fumigation is the only registered chemical for controlling post-harvest decay on litchi in South Africa but has issues with residue limits and decay levels.
• The study tested several fungicides and mixtures as dip treatments, in ambient (24°C) and heated (52°C) solutions, to find alternatives to sulfur dioxide.
• Heated fungicide solutions generally performed better than ambient ones when fungicides were tested alone, except fludioxonil, which was more effective in ambient solutions.
• Fungicide mixtures, especially prochloraz combined with fludioxonil, showed the best control of decay after simulated export and storage.
• Fludioxonil alone at 300 ppm was highly effective, better than at 600 ppm, suggesting possible phytotoxicity at higher concentrations.
• Prochloraz and guazatine mixtures also reduced post-harvest decay significantly compared to controls and single fungicides alone.
• Some fungi and yeasts remained problematic despite fungicide treatments, leading to still unacceptable decay percentages in some cases.
• Guazatine alone was not effective in general decay control but can control yeast-like pathogens, making it useful in mixtures.
• The treatment with prochloraz performed significantly better in heated solutions, but heating solutions adds costs to post-harvest processes.
• The study concludes fludioxonil and prochloraz, alone or in mixtures, show promise for reducing post-harvest decay of litchi fruit, with dose optimization needed.
• Heating fungicide dip solutions should be evaluated cautiously due to cost implications and mixed efficacy results.
• The study recommends further research on optimum concentrations and combinations to control a broad spectrum of pathogens affecting litchi post-harvest decay.