Aminocyclopyrachlor has provided excellent control of many perennial weed species including leafy spurge, but control of yellow toadflax has been inconsistent. 14C-aminocyclopyrachlor absorption was rapid in both leafy spurge and yellow toadflax and averaged 72% 48 h after treatment (HAT). However, translocation within the plant differed by species. More 14C translocated to the aboveground portion of yellow toadflax (28% of applied) compared to leafy spurge (16.5% of applied). There was rapid translocation of 14C-label to the roots of both species but more reached the belowground portion of leafy spurge than yellow toadflax. Over 12% of applied 14C translocated into leafy spurge roots within 24 HAT but declined to 2% by 192 HAT. In comparison, only 2% of applied 14C was found in yellow toadflax roots 24 HAT, and just 0.15% remained in belowground plant parts by 192 HAT. The inconsistent long-term control of yellow toadflax with aminocyclopyrachlor is likely due to poor translocation to the root system, which would allow for rapid regrowth in this hard to control perennial species.
Nomenclature: Aminocyclopyrachlor; leafy spurge, Euphorbia esula L. EPHES, yellow toadflax, Linaria vulgaris P. Mill. LINVU.