Synergic toxicity and field effect of pyraclostrobin and difenoconazole against Colletotrichum gloeosporioides on walnut

【Objective】The synergistic toxicity and field control effects of pyraclostrobin, difenoconazole and their mixtures against Colletotrichum gloeosporioides on walnut were studied in order to provide the information for integrating walnut anthracnose management.【Method】Toxicity of pyraclostrobin, difenoconazole and their mixtures at different ratios against C. gloeosporioides on walnut was determined by mycelial growth rates test. The field control effects of pyraclostrobin, difenoconazole and their mixtures on anthracnose were assessed by fungicide spray on walnut trees in the field.【Result】The results of co-toxicity test showed that the mixtures with the pyraclostrobin-difenoconazole mass ratio of 3:2 and 1:1 exhibited synergistic interaction, with the synergistic coefficients of 1.61 and 1.57, respectively. The other ratios exhibited an additive effect on anthracnose, with the synergistic ratio of 0.91-1.41. The field trials demonstrated that the mixture at 3:2(pyraclostrobin and difenoconazole were 150 g/L and 100 g/L in the mixture, respectively) mass ratio of 250 g/L pyraclostrobin EC and 250 g/L difenoconazole EC controlled the anthracnose efficiently. After spraying the mixture 125.0, 166.7 and 250.0 mg/L on walnut trees for three times, the control effects were all above 80%, equivalent to those of 325 g/L difenoconazole·azoxystrobin SC(125 g/L difenoconazole+200 g/L azoxystrobin) 162.5, 216.7 and 325.0 mg/L, respectively. 250 g/L difenoconazole EC 125.0 mg/L also exhibited good control effect, while 250 g/L azoxystrobin SC 166.7 mg/L and 250 g/L pyraclostrobin EC 166.7 mg/L gave slightly lower efficacy.【Conclusion】The mixture of pyraclostrobin and difenoconazole at 3:2 mass ratio exhibits synergistic interaction on the mycelial growth of C. gloeosporioides and controlls the anthracnose efficiently. Thus it can be widely applied on the disease management.