Of the 1,200 single spore isolates of Alternaria mali causing apple leaf spot and fruit decay, the mycelial colonies showed 76, 96 and 15% growth at 100,000

of captafol, chlorothalonil and folpet, respectively, and five and three percent growth at 10,000

of iprodione and polyoxin. These isolates showed cross-tolerance of mycelial growth, spore formation, or spore germination to the above five fungicides plus captan, garbenda, and thiophanate methyl. Captafol, mancozeb, polydong, and propineb did not show any cross-tolerance of spore germination since no spore was germinated at 100

which was much lower than the concentration used by apple growers. Benomyl, fenarimol, oxidong, and triademefon showed medium degree of cross-tolerance of the fungal growth, sporulation, and spore germination.