Dose-response of five weed species to indaziflam and oxadiazon

Authors: Ramanathan, Shwetha; GANNON, TRAVIS - North Carolina State University; MAXWELL, PATRICK - North Carolina State University

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Preemergence herbicides are applied in the beginning of spring to control the emergence and subsequent growth of summer annual weeds in turfgrass systems. Herbicide application timings should be optimized to ensure that enough of the applied herbicide concentration is present throughout the duration of weed emergence, which may range from a couple of months to half a year depending on the species. This research quantified the herbicide concentration required for control of five weed species and investigated the extent of control that is maintained from a single herbicide application during the respective emergence periods of these species in North Carolina. This information can help turfgrass managers adjust herbicide application timings based on the target weed species.

Technical Abstract: Indaziflam and oxadiazon are efficacious PRE herbicides used in warm season turfgrass due to their persistence and residual activity. It is beneficial to quantify effective concentrations for PRE control of summer annual weeds and determine whether these concentrations are maintained throughout weed emergence periods. Therefore, greenhouse bioassays were conducted with barnyardgrass, broadleaf signalgrass, doveweed, large crabgrass, and purple nutsedge. Treatments included indaziflam at 0, 4, 8, 12, 17, 21, 25, 29, 33, and 37 g ai ha-1 or oxadiazon at 0, 420, 841, 1,260, 1,681, 2,102, 2,354, 2,942, 3,363, and 3,783 g ai ha-1. Although PRE herbicides are not used to control perennial weeds, purple nutsedge was included to investigate the effect of selected herbicides on growth of this species. Herbicide EC50, EC80, and EC90 for seedling emergence inhibition and shoot and root mass reduction were quantified from log-logistic dose-response curves. Herbicide concentration that remains from a PRE application during the regional species-specific periodicity of emergence was predicted using first-order kinetics equations. Indaziflam and oxadiazon controlled seedling emergence 14 DAT in the evaluated annual weeds and shoot and root mass in all species 84 DAT. Indaziflam applied in mid-March at 33 g ai ha-1 may provide up to 90% seedling emergence inhibition in large crabgrass and signalgrass; up to 80% in barnyardgrass; and up to 50% in doveweed. Oxadiazon applied in mid-March at 3,363 g ai ha-1 may provide up to 80% seedling emergence inhibition in all species. Indaziflam and oxadiazon may control up to 80% shoot mass and up to 50% root mass, respectively, in purple nutsedge and 80 to 90% shoot or root mass in other species. Such information is useful in evaluating adequacy of herbicide management practices for season-long weed control and aids turfgrass managers in applying PRE herbicides at optimal timing based on target weed species.