Common lespedeza is a problematic summer annual weed in bermudagrass lawns, with limited PRE herbicides available for control. Dithiopyr is a pyridine herbicide primarily used for PRE grassy weed control but has shown potential efficacy for controlling annual legumes. The objectives of this research were to evaluate efficacy and behavior of dithiopyr in common lespedeza. In a 3-yr field experiment, sequential dithiopyr applications at 0.42 or 0.56 kg ai ha⁻¹ beginning in late winter and single applications of dithiopyr at 0.56 kg ai ha⁻¹ in spring controlled common lespedeza ≥ 88%. Single and sequential applications of indaziflam at 0.035 and 0.053 kg ai ha⁻¹ provided poor control (< 70%) of common lespedeza by late summer. In laboratory experiments, bermudagrass and common lespedeza had similar foliar absorption of ¹⁴C-dithiopyr, averaging 10% of the ¹⁴C applied, and both species retained > 80% of ¹⁴C in the treated leaf at 72 h after treatment (HAT). Common lespedeza translocated 6 times more root-absorbed ¹⁴C to shoots than bermudagrass and had 2.8 times greater absorption (Bq mg⁻¹) at 72 HAT. In metabolism experiments, parent herbicide levels measured ≥ 84% of extracted ¹⁴C in both species at 1, 3, and 7 d after treatment. Overall, dithiopyr effectively controls common lespedeza in bermudagrass as a PRE treatment in spring. Susceptibility of common lespedeza to dithiopyr is associated with acropetal translocation and greater herbicide concentrations compared with a tolerant species, bermudagrass.

Nomenclature: Common lespedeza (Kummerowia striata (Thunb.) Schindl.) ‘Kobe’; bermudagrass (Cynodon dactylon × C. transvaalensis Burtt-Davy) ‘Princess 77’.