Persistence and Degradation of Residues of Ciba C-9491 and Their Control of Fall Armyworms and Corn Earworms123

Abstract

Persistence of Ciba C-9491 ( O- (2,5-dichloro-4-iodo-phenyl) O, O -dimethyl phosphorothioate), its oxygen an-and its phenol, over 16 days, was determined in 3 plant parts of sweet corn treated with ½, 1, and 2 Ib per of an emulsifiable concentrate of C-9491. Highest residues occurred in stalks and leaves treated with 2 Ib per acre. During the 16 days, residues of G-9491 declined from 50.8 to 3.28 ppm, and those of the O-analogue diminished from 0.086 to <0.005 ppm. Residues of the reached their maximum (4.90 ppm) I day post treatment and remained rather constant during the ensuing 15 days. LD50 values for 4-day-old 30-mg larvae of fall armyworm, Spodoptera frugiperda (J. E. Smith), treated topically with acetone solutions of C-9491, its oxygen analogue, and its phenol were about 1.2, 0.2, and 200 µ.g, respectively. Feeding trials in the laboratory showed that the C-9491 was as good as or better than p, p’ -DDT in controlling the larvae. Slightly less effective control of fall armyworms and corn earworms, Heliothis zea (Boddie), was obtained in field plots of sweet com treated 6 times (2- to 3-day intervals) with I Ib per acre C-949 I than in similar plots treated with 2 Ib per acre DDT. The accumulation of residues of C-9491 and the 2 metabolites during these treatments was determined. Also, recoveries of the 3 compounds from field samples were compared by using 2 methods of extraction.