Residues of 4-(2,4-Dichlorophenoxy)butyric Acid in Winter Wheat 1

Residue data were collected during a 1-year field investigation to support a label amendment for the use of 2,4-DB (4-[2,4-dichlorophenoxy]butyric acid) in small grains. The 2,4-DB was applied to ‘blue boy’ winter wheat (Triticum aestivum L.) at the “recommended” and “twice the recommended” rates as the dimethylamine salt (1.68 and 3.36 kg ai [active ingredient]/ha) and the isooctyl ester (1.12 and 2.24 kg ai/ha). Low levels of 2,4-DB residues (4.9–7.4 ppmw) were found in wheat straw harvested 70 d after spraying with the isooctyl ester formulation, but no 2,4-DB residues were found in wheat straw treated with the dimethylamine form. The grain did not contain detectable levels of 2,4-DB or 2,4-D [(2,4-dichlorophenoxy] acetic acid) residues from any 2,4-DB treatment. No difference in yield between the control and 2,4-DB-treated plots was obtained. Rainfall that occurred 4 h after application may have resulted in some loss of the herbicide and the data presented should be considered preliminary.