Fate of Fluazinam in Pepper and Soil After Application

To discover the fate of fluazinam after its application in pepper field, an efficient residual analytical method for determining fluazinam in pepper and soil was developed. The samples were extracted by acetone, cleaned up by solid-phase extraction （SPE） florisil cartridge, and determined by gas chromatography with electronic capture detector （ECD）. The recoveries ranged from 80 to 94.6%, with repeatability relative standard deviation ≤9.3% at spiking levels of 0.1-1 mg kg^-1. The residue dynamics of fluazinam in pepper and soil were studied in a field plot. The experiment data showed that the halflives of fluazinam in peppers and soils were 2.5-3.7 days and 1.2-4.2 days, respectively. When the pepper was treated by fluazinam 50% suspension concentrate （SC） at 495 g ha^-1 4 times at 7-day intervals, the fluazinam in pepper on the 7th day after the last application was all below 0.06 mg kg^-1, which was below the maximum residue limit （MRL） fixed in Korea （0.3 mg kg^-1）. It is implied that fluazinam in pepper is nonpersistent. The results suggested that fluazinam 50% SC should be used in a pepper field at most for 4 times, and the pre-harvest interval should be 7 days.

Sensitivity assessment of Phytophthora nicotianae to fungicides of fluazinam and its mixture with carboxylic acid amide

Tobacco black shank caused by Phytophthora parasitica var.nicotianae(Breda de Hean)is one of the most serious diseases in tobacco growing,and few effective fungicides are available currently.The purpose of this study was to assess the feasibility of using fluazinam to treat tobacco black shank disease.In vitro toxicities of fluazinam to 62 isolates of P.nicotianae were determined by mycelial growth rate method.The EC50 values ranged from 0.294 6 to 2.389 9 μg/mL with a mean of 1.084 0 μg/mL.The sensitivity distribution was unimodal,and there was no resistant isolate in P.nicotianae population.The carboxylic acid amide(CAA)fungicides were single-site in action and activity to oomycetes.The synergistic interactions were tested by Wadley method between fluazinam and dimethomorph,flumorph,mandipropamid,respectively.The mixture containing dimethomoph:Huazinam at 1:2 ratio showed additive actions,with the synergy ratio of 1.2.The mixture containing flumorph and fluazinam at 1:5 ratio had the highest synergy ratio(SR 2.07).Mandipropamid and fluazinam had an additive interaction and the proportion of 2:1 had the lowest EC50 value(0.020 7 μg/mL).This study demonstrated the sensitivity of P.nicotianae to fluazinam,and provided the experimental foundation to use fluazinam for tobacco black shank management.

Repeated exposure of fluazinam fungicides affects gene expression profiles yet carries no costs on a nontarget pest

Fungicides are used to control pathogenic fungi of crop species,but they have also been shown to alter behavioral,life history and fitness related traits of nontarget insects.Here,we tested the fungicide effects on feeding behavior,survival and physiology of the nontarget pest insect,the Colorado potato beetle(CPB)(Leptinotarsa decemlineata).Feeding behavior was studied by a choice test of adult beetles,which were allowed to choose between a control and a fungicide(fluazinam)treated potato leaf.Larval survival was recorded after 24 and 72 h exposure to control and fungicide-treated leaves with 2 different concentrations.The adults did not show fungicide avoidance behavior.Similarly,survival of the larvae was not affected by the exposure to fungicides.Finally,to understand the effects of fungicides at the physiological level(gene expression),we tested whether the larval exposure to fungicide alter the expression of 5 metabolic pathway and stress associated genes.Highest concentration and 72-h exposure caused upregulation of 1 cytochrome P450(CYP9Z14v2)and 1 insecticide resistance gene(Ldace1),whereas metabolic detoxification gene(Ugt1)was downregulated.At 24-h exposure,highest concentration caused downregulation of another common detoxification gene(Gs),while both exposure times to lowest concentration caused upregulation of the Hsp70 stress tolerance gene.Despite these overall effects,there was a considerable amount of variation among different families in the gene expression levels.Even though the behavioral effects of the fungicide treatments were minor,the expression level differences of the studied genes indicate changes on the metabolic detoxifications and stress-related pathways.