Root exudation of diclofop-methyl from treated ryegrass (Lolium spp.) and durum wheat (Triticum durum desf.)

Experiments were conducted to evaluate the occurrence and significance of release of diclofop-methyl through the roots of treated ryegrass and wheat. The study with C-14-diclofop-methyl indicated a basipetal translocation of foliar applied active ingredient for both ryegrass and wheat The root translocation of the herbicide was significantly higher in wheat than in ryegrass. By 20 days after the treatment (DAT), approximately 2.5% and 1.5% of the absorbed radiolabel were found in wheat and ryegrass roots, respectively. No root exudation of C-14-diclofop-methyl from wheat plants was observed. In contrast, the amount of the C-14-label found in the growing medium of ryegrass 20 DAT was ranged from 0.16% to 0.92% of the herbicide absorbed. Single ryegrass plant growing in isolated pot exuded 0.16 +/- 0.11% of the absorbed active ingredient, while treated ryegrass plants growing in the same medium of untreated ryegrass or wheat plants exuded 0.53 +/- 0.22% and 0.93 +/- 0.37% of the absorbed herbicide, respectively. Electronic autoradiography of thin layer chromatography plates of rooting medium indicated unmetabolized diclofop-methyl and diclofop acid as the major C-14-labeled compounds (> 95%). No subsequent uptake of exuded C-14 by untreated plants (ryegrass or wheat) sharing the growing medium of treated ryegrass was observed.