Physical Modes of Action of Azoxystrobin and Its Biokinetics for Controlling Haricot Bean Leaf Blight Caused by Rhizoctonia solani

Compared with carbendazim and thiram,the inhibitory activity of azoxystrobin to mycelial growth of Rhizoctonia solani,the pathogen of rice sheath blight,was tested in vitro,and the physical modes of action of azoxystrobin and its biokinetic properties for controlling haricot bean leaf blight caused by R.solani were evaluated by detached leaf methods.The EC50 values of azoxystrobin, carbendazim and thiram against mycelial growth of R.solani on PDA were 0.072 4 μg /mL,1.134 4 μg /mL and 1.202 6 μg /mL,respectively.When the pathogen was inoculated immediately after fungicide application,the protective efficacy of azoxystrobin (250 μg/mL),carbendazim (500 μg /mL) and thiram (1 000 μg /mL) for controlling haricot bean leaf blight were 95.61%,99.88% and 81.45%, respectively; when the pathogen was inoculated 3 days after fungicide application,the protective efficacy of azoxystrobin,carbendazim and thiram were 92.27%,100% and 46.96%,respectively; and when the fungicides were applied 36 hours after inoculation the curative efficacy of azoxystrobin,carbendazim and thiram were 90.40%,95.75% and 61.94%,respectively.These results indicated that azoxystrobin had not only very good protection and retention but also excellent curative action.When the fungicides were applied on the leaf base but the pathogen was inoculated on the untreated leaf tip,the protective efficacy of azoxystrobin,carbendazim and thiram for controlling haricot bean leaf blight were 87.81%,42.09% and 7.24%,respectively; when the fungicides were applied on the abaxial (lower) leaf surface but the pathogen was inoculated on the untreated adaxial (upper) surface,the protective efficacy of azoxystrobin,carbendazim and thiram were 87.30%,37.00% and 16.15%,respectively.It demonstrated that azoxystrobin had both excellent xylem systemic translocation and translaminar movement in haricot bean leaves.