Screening fungicide for pathogen inhibition and disease control of apple tree valsa canker.

The inhibitory effects of 10 fungicides on apple tree valsa canker were compared on dishes and twigs.The results showed that conidia germination and mycelial growth were inhibited by all fungicedes tested.The EC50 value of Difenoconazole was 6.1×10-3 μg·mL-1,the lowest among tested fungicide in inhi-biting conidia germination.Tebuconazole and Imazalil also showed obvious inhibition effect.Thiophanate-methyl was the least efficient with the EC50 value 2.6×101 μg·mL-1.Difenoconazole also showed the highest activity for inhibiting mycelial growth with EC50 value of2.3×10-2 μg·mL-1.Tebuconazole was better than other fungicide.Thiophanate-methyl and Propineb were the least efficient with quite high EC50 value.Furthermore,the size of the lesion after inoculation on excised twigs also revealed that Difenoconazole was most efficient because it showed the smallest lesion of 394 mm2 compared with other tested fungicides.So Difenoconazole and Tebuconazole could be used to control apple tree valsa canker in field to subsititute forbided fungicides such as asomate.