Marssonina blotch, caused by the fungus Marssonina coronariae, is a serious foliar disease on apple in East Asia as well as in other moist temperate regions in Asia, Europe, and South America. Several fungicides were investigated for their toxicity to mycelial growth and conidial germination of the pathogen in vitro. Tebuconazole, kresoxim-methyl, hexaconazole, propiconazole, and a mixture of tebuconazole and benziothiazolinone sharply inhibited mycelial growth but had less effect on conidial germination. Field tests were conducted in a commercial orchard in Baishui County, Shaanxi Province, China, during 2012, 2013, 2014, and 2015 in order to develop recommendations for apple growers. Three applications of tebuconazole, hexaconazole, propiconazole, or a mixture of tebuconazole and benziothiazolinone at 20-day intervals from early July to late August resulted in defoliation incidence of <5%. When sprays of Bordeaux mixture + tebuconazole, Bordeaux mixture + propiconazole, and Bordeaux mixture + tebuconazole and benziothiazolinone were alternated, the spray interval was extended to 25 days and defoliation incidence remained <5%. Based on historical records and our results, scouting for symptoms should begin in mid-June. We recommend commencing the spray period in early July in years with normal rainfall patterns, and spraying in mid- to late June in years with much rainfall. The findings of this study create a foundation for implementation of an efficient spray program against Marssonina leaf blotch in apple orchards in the Loess Plateau Region of China.

Alternaria spp. are pathogens of several diseases that pose significant threats to apple production. Several putative Alternaria sp. isolates were obtained from lesions of a disease commonly referred to as black dot on apple fruit in Shaanxi Province, China. Pathogenicity tests using mycelial plugs and conidial suspensions indicated that this isolate could cause leaf blotch, as well as moldy core and black dot on fruit. On the basis of sequence analysis of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RNA polymerase second largest subunit, and translation elongation factor 1-α, an isolate clustered with the Alternaria sect. Ulocladioides. By combining GAPDH, major allergen Alta1, mating type protein 1-2-1, and the AGA1 gene sequence analysis and morphological description, the isolates were identified as a new species named Alternaria malicola. Our finding expands the documented diversity of apple pathogens within the genus Alternaria and clarifies the taxonomy of the pathogen assemblage that may be associated with three apple diseases.

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