- S H Swart
- QMS Agri Science, P O Box 416, Letsitele 0885, South Africa
- 2006
Fumigation sulphur is the only chemical registered to control post-harvest decay on litchi fruit in South Africa. Prochloraz is registered for post-harvest treatments on several other crops with maximum residue levels set according to harmonized European union standards. In January 2005 a trial was conducted to evaluate the effect of prochloraz at different concentrations, applied as dip treatments, in fungicide solutions at ambient temperature. During December 2005 this trial was repeated with some variation in concentrations evaluated, and with the addition of hot dip (52°C) treatments. Results in January 2005 showed the percentage decayed fruit in the control treatment was 45%, which was significantly higher than any treatment with prochloraz, after seven days of incubation at ambient temperature. The percentage decayed fruit decreased with increasing concentrations of prochloraz. The best control of post-harvest decay was obtained when fruit was dipped in 810 ppm prochloraz solution. Results in December 2005 showed that the percentage affected fruit was significantly lower after three and seven days incubation at ambient temperature for all test solutions (applied at ambient temperature) containing more than 337.5 ppm prochloraz, compared to the untreated control treatment and concentrations with less than 90 ppm prochloraz. The best control of post-harvest decay was achieved with concentrations of 1620 ppm prochloraz, followed by 2250 ppm, 810 ppm and 1125 ppm prochloraz, in order of efficacy. Concentrations lower than 202.5 ppm prochloraz seemed to be less effective. Trends indicated that heated solutions at concentrations of 90 ppm prochloraz and higher, gave good control of post-harvest decay at three days after removal from cold storage. When evaluated seven days after removal from cold storage, dosages of 810 ppm and higher were slightly superior to the lower concentrations, although not statistically. Results, therefore, indicated that heating of the fungicide solution might have an initial advantage up to three days after removal from cold storage, but that shelf life is probably compromised due to heating of fungicide solutions, when fruit is kept for longer periods. The negative effect of heated dip solutions was also observed for control treatments, showing an increase from 75% affected fruit when dipped in water at ambient temperature, compared to 98% affected fruit when dipped in heated water.
Summary:
Sulfur fumigation is the only registered chemical for post-harvest decay control on litchi in South Africa, but there is a need for alternative fungicides due to residue limitations.
Prochloraz, registered for post-harvest use in other crops, was evaluated as a dip treatment at various concentrations (45 to 3240 ppm) at ambient and heated (52°C) temperatures on ‘Mauritius’ litchi fruit.
Trials were conducted in January and December 2005 with untreated litchi fruit stored at 3 ± 1°C for 28 days, followed by incubation at 25 ± 2°C to assess decay.
Results showed significantly less decay in fruit treated with prochloraz compared to controls, with the best control achieved at around 810 ppm concentration.
Higher concentrations (1620 and 3240 ppm) sometimes caused phytotoxic effects (darkening, softening), while 810 ppm showed no phytotoxicity.
Decay-causing fungi reduced by prochloraz included Alternaria spp. and Botryodiplodia sp., but an unknown fungus increased with higher prochloraz, likely due to niche opening after suppression of other fungi.
Heated prochloraz solutions initially provided better decay control shortly after cold storage removal, but after seven days, decay levels were similar or higher compared to ambient treatments.
Heated dips also caused slight fruit discoloration and overall compromised shelf life compared to ambient treatments.
Residue analysis showed prochloraz residues in treated fruit well below maximum residue levels allowed on other fruits, with residues decreasing after 28 days.
Taste panel evaluations detected no off-flavors or effects on sugar content (Brix) from prochloraz treatments.
The study recommends about 810 ppm prochloraz at ambient temperature as effective for post-harvest decay control in litchi, with residue safety and no negative sensory effects.
For broad-spectrum decay control and resistance management, fungicide mixtures might be more effective due to multiple fungal pathogens causing decay.
The study highlights the need for alternative decay treatments as sulfur residue limits tighten, with prochloraz as a promising option under proper concentration and temperature conditions.