Comparison of the uptake, movement and metabolism of fluroxypyr in Stellaria media and Viola arvensis

Summary The uptake, movement and metabolism of fluroxypyr* is compared in two contrasting weed species, Stellaria media (susceptible) and Viola arvensis (moderately resistant). Similar rates of uptake occurred in both species, with a rapid cuticular uptake of 50% of that applied within 4 h. Total uptake by the underlying leaf tissue reached 66.6% and 70.8% in S. media and V. arvensis after 7 days. In translocation studies, in which 14C‐fluroxypyr was applied to previously sprayed plants, 5.1% of applied 14C‐activity was translocated from the treated leaves of S. media after 1 day, which increased to 42.2% after 7 days, recovered mainly from the stem tissue. In V. arvensis translocation was similar after 24 h however, after 7 days over 40% of applied 14C‐activity remained in the treated leaves and only 9.7% was translocated, mainly to the developing leaves and apical tissue. 14C‐activity extracted from the cuticle was the methylheptyl ester of fluroxypyr in both species. In the treated leaves and apical tissue, 14C‐activity was the free acid of fluroxypyr and polar conjugates with a significantly greater proportion of the acid in S. media. It is concluded that the resistance or V. arvensis is partially due to reduced translocation and greater conjugation than in the susceptible S. media.