Residues of the quinone outside inhibitor fungicide trifloxystrobin after postharvest dip treatments to control penicillium spp. On citrus fruit

The effectiveness of postharvest dip treatments with trifloxystrobin (TFX) in controlling green and blue mold (incited by Penicillium digitatum and P. italicum respectively) of citrus fruit was investigated in comparison with imazalil (IMZ). Residues retained by fruit were determined as a function of treatment time, dip temperature and storage conditions. Trials on ‘Avana apireno’ mandarins artificially inoculated with P. digitatum or P. italicum showed that treatments with 200 to 600 mg/l active ingredient (a.i.) TFX at 20°C were less effective than 100 mg/l TFX at 50°C in controlling P. digitatum but equally effective in controlling P. italicum development. IMZ treatments with 200 mg/l IMZ at 20 °C or 25 mg/l IMZ at 50°C resulted in over 98% reduction of P. digitatum and ca 93% reduction of P. italicum development with respect to untreated fruit. Total suppression of pathogens was achieved when higher IMZ doses were applied. Studies on artificially wounded lemons, oranges, clementines and mandarins revealed that treatment with 100 mg/l TFX at 50°C effectively controlled decay development (mainly due to P. digitatum) after seven days of storage at 20°C. These results were confirmed on non-wounded oranges cv. ‘Tarocco’ and grapefruits cvs. ‘Marsh Seedless’ and ‘Star Ruby’ during 3 weeks of simulated quarantine at 1°C, plus storage (5 weeks at 8°C, oranges or 8 weeks at 11°C, grapefruits) and an additional 1 week of simulated marketing conditions (SMP) at 20°C. IMZ at 50°C was highly effective in controlling decay during storage and SMP. TFX treatment at 50°C was as effective as IMZ in controlling decay in most samples. After treatment with 100 mg/l TFX at 20°C, fungicide residues in ‘Tarocco’ oranges doubled from 0.15 mg/kg to 0.30 mg/kg when dip time increased from 0.5 to 3 min, whereas when treatments were performed at 50°C TFX residues were not related with dipping time. Residues of TFX were significantly correlated with dip temperature. A 3-min dip treatment at 50°C produced a deposition of TFX ca 2-fold higher than when treatments were carried out at 20°C.