Pg. 66-70 Post-harvest control of diseases of litchi fruit with prochloraz

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.