Field efficacy of the combination of famoxadone and metalaxyl-M against Plasmopara viticola and the residue dynamics of the two fungicides in grape

To clarify the feasibility and safety of using the combination of famoxadone and metalaxyl-M against Plasmopara viticola in grape, the indoor co-toxicity test, field control efficacy test and residue behavior test were carried out. The results showed that the type of joint effect was synergistic on P. viticola when the ratio of famoxadone and metalaxyl-M was 1 : 1, with the EC₅₀ value was 2.52 mg/L and the co-toxicity coefficient was 154.53. The best field control efficacy of 30% famoxadone + metalaxyl-M SC (at the mass ratio of 1 : 1) against P. viticola was 83.9% after 3 times of application at the dosage of 120-200 mg a.i./kg with interval of 7 d. The control effect of 30% famoxadone + metalaxyl-M SC at the dosage of 200 mg a.i./kg was significantly better than that of 68.75% famoxadone + mancozeb WG at the dosage of 687.5 mg a.i./kg, and the control effect of 30% famoxadone + metalaxyl-M SC at the dosage of 120 and 150 mg a.i./kg was significantly better than 68% metalaxyl-M + mancozeb WG at the dosage of 1360 mg a.i./kg. At the spiking levels of 0.1, 0.5 ,1.0 and 5.0 mg/kg, the average recoveries of famoxadone and metalaxyl-M in grape were 91%-107% and 92%-107%, respectively, with RSD less than 5.7%. The dissipation of famoxadone and metalaxyl-M in grape fitted to the first order kinetics and the half-lives were 8.9-12.8 d and 7.4-10.0 d, respectively, indicating that they were easily dissipated pesticides. The results suggested that the formulation of 30% famoxadone + metalaxyl-M SC (at the mass ratio of 1 : 1) could be an effective fungicide for controlling P. viticola, with the characteristics of high efficiency, low residual, easily degraded, and safe for use, and have certain future developmental value.