Residues of Phorate and Five of Its Metabolites: Their Persistence in Forage Corn and Grass12

Coastal bermudagrass, Cynodon dactylon (L.) Pers., and corn, Zea mays L., field treated with an emulsifiable concentrate of phorate, at 0.5, 1.0, and 2,0 lb (active ingredient) per acre and sampled 0, 1, 7, 14, 21, and 28 days posttreatment were analyzed for residues of the parent compound and 5 of its metabolites. In corn, total residue consisting of the parent compound (P=S, S), its sulfoxide (P=S, SO) and sulfone (P=S, SO2), and phoratoxon sulfoxide (P=O, SO) and phoratoxon sulfone (P=O, SO2), was less than 1.0 ppm 14 days posttreatment for all 3 rates of application. Residues of phoratoxon (P=O, S) were not detected in any corn samples. Total residues in grass, consisting of the same metabolites found in corn, were found to be less than 1.0 ppm 21 days posttreatment. In corn silage, made from 1-day post-field treatments of corn at the 3 rates of application and ensiled at 85°F for 30 days in glass jars, the residues consisted mainly of phorate, its sulfoxide and sulfone, and phoratoxon sulfoxide which were relatively stable.