Efficacy of heat treatments with water and fludioxonil for postharvest control of blue and gray molds on inoculated pears and fludioxonil residues in fruit

The residue levels of fludioxonil (FLU) were determined in pear cultivars Precoce di Fiorano, Coscia, and Spadona estiva after a 2-min dip in an aqueous mixture of FLU containing 300 or 100 mg/liter of active ingredient at 20 or 50°C and after 12 days at 17°C and 80% relative humidity (simulated shelf life conditions). The accumulation trend of FLU residues was determined in ‘Precoce di Fiorano’ pears after treatments with 25, 50, 100, or 200 mg/liter of active ingredient at 20 or 50°C for 2 min or at 60°C for 1 min. The efficacy of heat treatments with water and FLU was investigated on artificially inoculated ‘Precoce di Fiorano’, ‘Coscia’, and ‘Spadona estiva’ pears for the control of postharvest blue mold and gray mold caused by Penicillium expansum and Botrytis cinerea, respectively. Treatment with 300 mg/liter FLU at 20°C resulted in residue levels similar to those from treatment with 100 mg/liter FLU at 50°C in ‘Coscia’ fruit but in significantly lower residues in ‘Precoce di Fiorano’ and ‘Spadona estiva’ pears. Post–shelf life residues decreased in all cultivars, especially in ‘Spadona estiva’ pears treated with 300 mg/liter FLU at 20°C. Residue levels of FLU in ‘Precoce di Fiorano’ pears treated at 20, 50, or 60°C were correlated with fungicide dosage. When an equal rate was used, treatment at 50°C resulted in a higher and a notably higher FLU deposition than that found under treatment at 60 and 20°C, respectively. The in vitro tests showed that both pathogens were very sensitive to FLU, with MICs averaging 0.05 and 0.1 mg/liter for B. cinerea and P. expansum isolates, respectively. The 50% effective concentration ranged between 0.01 and 0.05 mg/liter for B. cinerea and between 0.05 and 0.1 mg/liter for P. expansum. In the in vivo trials, hot water treatment effectively reduced the incidence of both diseases during the first 4 to 8 days, depending on cultivar, dip temperature, and type of inoculum. However, as the incubation time proceeded, decay reduction was generally lower and the benefit of heat treatments was notably reduced or almost lost. In contrast, all treatments with FLU had a long-lasting effect. Treatments with heated FLU were more effective than those with unheated FLU; reduced concentrations of active ingredient were required to achieve a comparable control of blue and gray mold decay in these pears.