Archivio Journal of Plant Pathology

Abstract:

The susceptibility of pear leaf and fruit at their early development stages to Septoria pyricola and the chemical control of the disease were studied. Unfolded or fully expanded leaves and young fruit were susceptible to infections, when artificially inoculated. With an average temperature of 14oC, relative humidity of 70% and increased leaf wetness for at least 6 hours during the night, the characteristic disease symptoms, on both leaves and fruits, were developed within two to three weeks. Pycnidia were not formed on fruit and their infection was confirmed by applying Koch’s postulates. Surveys in pear orchards during 2010 revealed the predominance of isolates highly resistant to the benzimidazole fungicide carbendazim. Some isolates exhibited 10-fold reduced sensitivity to bitertanol (sterol demethylation inhibitors; DMI’s) but they were sensitive to kresoxim-methyl (quinone outside inhibitors; QoI’s) and to boscalid (succinate dehydrogenase inhibitors; SDHI’s). Bitertanol and flusilazole (DMI’s), azoxystrobin, kresoxim-methyl and trifloxystrobin (QoI’s) and the mixture of pyraclostrobin (QoI) plus boscalid (SDHI) controlled Septoria effectively when they were applied on five occasions, commencing at the stage of ‘inflorescence emergence’. The disease progress was ceased even in cases of only one application with either azoxystrobin or flusilazole at ‘inflorescence emergence’ stage. Carbendazim failed to control the disease when BenHR-resistant propagules were enclosed in the primary inoculum. The results indicate that the pear leaf and fruit are vulnerable to S. pyricola at early stages of development, whereas secondary formed inocula on leaves expanded the disease only within the tree canopy.