Studies into the differential activity of the hydroxybenzonitrile herbicides

Uptake, movement, and metabolism of unformulated ioxynil and bromoxynil salts were investigated in Matricaria inodora and Viola arvensis . The morphology of these two species did not give rise to different spray retention and contact angles. After 7 days, uptake of [ 14 C]ioxynil-Na reached 8.26% of applied 14 C activity in M. inodora and 16.77% of that in V. arvensis compared with 1.54 and 3.83%, respectively, for [ 14 C]bromoxynil-K. Over 98% of the 14 C activity detected in the plant after 7 days remained in the treated leaves of V. arvensis following [ 14 C]ioxynil-Na treatment. However, 8.7% of the 14 C activity detected in [ 14 C]ioxynil-Na-treated M. inodora was recovered from the apex and developing leaves reflecting a greater translocation. [ 14 C]Bromoxynil-K was more mobile in both species and after 7 days 87.5 and 91.39% were detected in the treated leaves of M. inodora and V. arvensis , respectively. In both species the majority of translocated 14 C activity was recovered from the apex and developing leaves. Up to 20% of the applied [ 14 C]ioxynil-Na and [ 14 C]bromoxynil-K was not detected within the treated plant. Extraction of treated plants revealed no detectable metabolic breakdown of ioxynil-Na to halogenated derivatives in either species. However, metabolic breakdown of bromoxynil-K was apparent in V. arvensis . No significant root exudation was detected when [ 14 C]ioxynil-Na and [ 14 C]bromoxynil-K were applied to hydroponically grown S. media and V. arvensis . Losses of 14 C activity were due to herbicide volatility or degradation to volatile products on the leaf surface.