Persistence and Activity of Norflurazon and Fluridone in Five Georgia Soils Under Controlled Conditions

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Abstract
Response of grain sorghum [Sorghum bicolor (L.) Moench. ‘BR 64’] to norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone] and fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)pyridinone} and the effect of previous treatment on the persistence of herbicide activity in five soils were determined in the greenhouse. Relative phytotoxicity of fluridone in the soils was ordered as Greenville sandy clay loam > Appling coarse sandy loam > Dothan loamy sand = Rome gravelly clay loam > Bradson clay loam. Phytotoxicity of norflurazon was ordered as Greenville = Appling = Dothan > Rome > Bradson. Fluridone was more phytotoxic than norflurazon. Field soil that has been previously treated with norflurazon or fluridone (500 days earlier at 1.7 kg ai/ha) still had low concentrations of each herbicide present at the time of retreatment in the greenhouse. Previous treatment of norflurazon did not affect the rate of decline in activity in any of the soils compared to previously nontreated soils except for Appling. Significantly higher concentrations of norflurazon remained in all previously treated soils 297 days after treatment (DAT) compared to previously nontreated soil. Residual carryover of norflurazon was greater in the Bradson soil (2.8% O.M.) than soils having less than 2% O.M. Fluridone dissipation was significantly faster in previously treated soil than in previously nontreated soil, indicating enhanced microbial degradation of the herbicide.