Effect of pre and postharvest application of fungicides on postharvest decay of Bosc pear caused by Alternaria- Cladosporium complex in North Patagonia, Argentina

In recent years, decays by Alternaria spp. and Cladosporium spp. constituted a hazard to "Bosc" pear fruit during cold storage with significant economic losses (about 50%) in the Rio Negro and Neuquen Valleys. Studies with new fungicides that potentially have good activity against these key pathogens of "Bosc" pears were carried out. During the years 2011, 2012 and 2013, commercial formulations of pyraclostrobin + boscalid (Pyr + Bosc), cyprodinil + fludioxonil (Cyp + Flu), fludioxonil (Flu), pyrimetanil (PyrM) and myclobutanil (Myc) were studied by in vitro and in vivo tests. Commercial formulations of Flu, PyrM and Myc were added to the study to be used and have a use register for pome fruits in Argentina. In vivo tests were applied postharvest on laboratory and semicommercial scale, and, preharvest, to orchard. In vitro tests showed high percentages of inhibition of mycelial growth and conidia germination of both Alternaria and Cladosporium, however Flu was highlighted in the inhibition of Alternaria (EC50 = 0.0014) and Pyr + Bosc to Cladosporium (EC50 = 1.14 x 10(-8)). In vivo assays on semi-commercial scale, showed that fungicides evaluated (Pyr + Bosc, Cyp + Flu, Flu and Pyr) applied postharvest only reduced the natural incidence of Alternaria-Cladosporiwn complex (4 months at - 1/0 degrees C), between 24 and 35%, while on wounds artificially inoculated, the reduction achieved was between 91 and 98%. These results suggest that for the control of Alternaria-Cladosporium complex in Bosc pears, postharvest interventions are insufficient. In this sense, the results obtained of preharvest application of Pyr + Bosc showed that the control of the incidence of this decay after 4 months of cold storage was 44.6% of Alternaria-Cladosporium and 95% of B. cinerea. The results of this study indicate that preharvest applications, with the fungicide Pyr + Bosc, reduce the incidence of decay in postharvest, so this might be an important strategy to reduce postharvest losses in the irrigated valleys of Rio Negro y Neuquen.