Cyproconazole, a New Postharvest Demethylation Inhibitor Fungicide to Manage Citrus Sour Rot and Green Mold Caused by DMI-Resistant Pathogens

Cyproconazole (CPZ) was identified as a new postharvest fungicide with incomplete cross-resistance to other demethylation inhibitor fungicides registered for managing major decays of citrus. CPZ was effective on lemons, oranges, grapefruit, and mandarins, significantly reducing sour rot (<i>Geotrichum citri-aurantii</i>) and green mold (<i>Penicillium digitatum</i>). In laboratory and experimental packing line studies, CPZ was compatible with other fungicides, performed well in fruit coatings, and was effective using different application systems. CPZ at 300 to 1,250 μg/ml reduced sour rot incidence of lemons inoculated with a propiconazole (PPZ)-moderately resistant (MR) isolate of <i>G</i>. <i>citri-aurantii</i> from 87.5% in the control to between 54.6 and 13.3%, whereas. green mold caused by an imazalil (IMZ)-resistant (R) isolate of <i>P. digitatum</i> was reduced from 99.0% in the control to between 59.9 and 20.8%. CPZ at 1,000, 2,000, and 4,000 μg/ml in aqueous or storage coating preparations generally performed statistically similar against PPZ-sensitive (S), MR, and highly resistant (HR) isolates of <i>G</i>. <i>citri-aurantii</i>. Sour rot was reduced to zero levels with increasing concentrations for S, and MR isolates, whereas decay caused by the HR isolate was reduced from 97.1% in the control to 26.0% in storage wax treatments. For green mold and sporulation control, storage and pack coatings generally reduced the performance of CPZ, PPZ, IMZ, fludioxonil + azoxystrobin, and mixtures compared with aqueous applications. CPZ was not as effective as IMZ or fludioxonil + azoxystrobin in reducing sporulation. There was no significant difference in efficacy between heated and ambient-temperature flooder applications of CPZ or PPZ in controlling sour rot or green mold. CPZ is currently undergoing registration for postharvest use on citrus in the United States and will be an effective treatment by itself and in mixtures with other fungicides for major decays caused by S and R pathogens.