Abstract:

Abstract： This study investigated the role of triazole fungicide，tebuconazole and difenoconazole were investigated in controlling the disease in vitro and in field. The fungicides showed a strong inhibition effect on mycelium dry weight，and acervuli formation and a less inhibition effect on conidiagermination by comparing EC₅₀value in vitro EC₅₀ values of tebuconazole on mycelium dry weight，acervuli formation and conidia germination were 0.060，0.055 and 128.825 μg·mL^.-1，respectively. EC₅₀ values of difenoconazole were 0.009，0.024 and 331.131 μg·mL^-1，respectively. Difenoconazole showed lower EC₅₀ values than tebuconazole on mycelium growth and acervuli formation on YD and CSA medium，respectively. The fungicides application in an orchard of Pucheng in 2005 and 2006 demonstrated that both fungicides gave high disease control efficacy in application of commended concentration compared to untreated control. Tebuconazole showed higher efficacy than difenoconazole，their control efficiency were 82.10% and 42.37% in 2005，and 81.83% and 62.38% in 2006，respectively. Azoxystrobin，which control efficiency was 88.74%，had no significant difference with tebuconazole. Therefore，alternative use of these fungicides 1～2 times in mid June was recommended to control Marssonina leaf blotch and avoid the resistance of the pathogen to fungicides in this region.

Key words: Key words： tebuconazole, difenoconazole, premature defoliation of apple, mycelium dry weight, conidia germination, disease control