Dithiopyr Efficacy, Absorption, and Fate in Annual Bluegrass, Goosegrass, Smooth Crabgrass, and Tall Fescue

Abstract

Dithiopyr provides pre‐ and early postemergence (POST) control of smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl] in tall fescue (Festuca arundinacea Schreb.), and may allow greater application flexibility in spring than other herbicides. Dithiopyr also provides preemergence (PRE) control of annual bluegrass (Poa annua L.) and goosegrass [Eleusine indica (L.) Gaertn.], but POST applications are ineffective and may result from differential physiological fate compared to smooth crabgrass. Experiments were conducted to investigate efficacy, absorption, distribution, and metabolism of dithiopyr in annual bluegrass, goosegrass, smooth crabgrass, and tall fescue. From seven dithiopyr rates, 1.18, 1.03, 0.76, and >4.48 kg a.i. ha−1 were required to reduce shoot mass 50% from the nontreated for annual bluegrass, goosegrass, smooth crabgrass, and tall fescue, respectively. In laboratory experiments, smooth crabgrass had ≈75% more kBq kg−1 following root absorption of 14C‐dithiopyr than annual bluegrass, goosegrass, and tall fescue after 72 h. All species recovered >90% of foliar‐absorbed 14C in the treated leaf after 72 h, with limited 14C recovery (≤5%) in roots and nontreated shoots. Metabolism of dithiopyr increased from 1 to 7 d after treatment (DAT) in all grasses. Final metabolism measured 69, 52, 33, and 27% of total 14C recovered in smooth crabgrass, goosegrass, annual bluegrass, and tall fescue, respectively. Results suggest relative herbicide concentration and greater metabolism is associated with dithiopyr selectivity for POST control of smooth crabgrass compared to other grassy weeds in turf.