Edifenphos

The Uses of Edifenphos

Edifenphos is a foliar applied contact fungicide that provides both protective and curative control of rice blast diseases caused by Pyricularia oryzae. It also controls ear blight and stem rot in rice.

The Uses of Edifenphos

Fungicide.

Definition

ChEBI: An organic thiophosphate that is the O-ethyl-S,S-diphenyl ester of phosphorodithioic acid. Used to control a variety of fungal diseases on rice including blast, ear blight and stem rot. Edifenphos i moderately toxic to mammals and fish but poses more of a risk to aquatic invertebrates.

Metabolic pathway

Hydrolytic cleavage of the P-0 and P-S linkages affords the major degradation and metabolic pathways of edifenphos. A unique transesterification reaction yielded tri-S-phenyl and di-O-ethyl phosphorus esters as minor products in soil and plant test systems (Scheme 1).

Degradation

The hydrolytic DT₅₀ values of edifenphos (1) at pH 7 and 9 at 25 °C were 19 and 2 days, respectively (PM). [³⁵S]Edifenphods egraded rapidly in aqueous solution when exposed to UV light at 25-28 °C [DT₅₀ ca. 3 days (light exposed) vs. 19 days (dark control)]. Cleavage of the P-S linkage is the primary degradation pathway. Thiophenol (2) was further oxidised to form diphenyl disulfide (3), possibly during sample extraction, isolation and analysis. Stepwise cleavage of the P-S and P-O linkages yielded O-ethyl S-phenyl hydrogen phosphorothioate (4), S-phenyl dihydrogen phosphorothioate (5), benezenesulfonic acid (6) and sulfuric acid as major ³⁵S-containing products, whereas O-ethyl dihydrogen phosphate (7) and phosphoric acid were recovered from the phosphorus portion of the molecule (Murai, 1977).

Toxicity evaluation

Edifenphos shows no delayed neuropathic symptoms. Safety intervals between spray and harvest for rice are 21 days in Japan with 0.2 mg of MRL (Maximum Residue Limit).