Control of postharvest fruit decays in relation to residues of 2,6-dichloro-4-nitroaniline and difolatan

Field spray applications in 1961 on peach and apricot indicated lasting residual activity of DCNA under the California environment of high temperature with no rain, and high activity of residual DCNA against Rhizopus stolonifer with 1 and with 0.5 pound of DCNA in 100 gallons of water. Some activity against R. stolonifer was observed with 1 pound of captan and of folpet. DCNA activity was comparable with that of captan and folpet on Monilinia fructicola on peach and apricot, but not on apricots that showed little to no DCNA residue after seven days.

Field sprays in commercial peach orchards during 1962 showed that three sprays of DCNA were more effective in control of Rhizopus rot of peaches than were one or two sprays when peaches were subsequently ripened in chambers held at 20° C and 80 per cent relative humidity. When treatments resulting in similar DCNA residues at harvest were compared, consistent reduction of Monilinia rot was shown only with the three spray applications. Dip treatments with ‘Halford’ peaches showed control of Rhizopus rot with a residue of 4 ppm DCNA and of Monilinia rot with a residue of a mixture of 28.4 ppm DCNA and 13 ppm Difolatan.

Residue analyses of field-sprayed peaches indicated the average half-life of DCNA to be about six days (half of original residue was present) under the arid environment of California when sprays were applied approximately four weeks before harvest.

Following canning, the peaches showed trace amounts of DCNA, but Difolatan could not be detected by the method of analysis used.