Abstract Mulch, mechanical removal, and herbicides are the most common weed control practices employed in landscapes. Previous research demonstrated preemergence herbicide efficacy in nurseries, but research in landscapes with and without mulching is limited. This research evaluated formulations of common preemergence herbicides for weed control in bare soil and mulched landscapes in Florida, Indiana, and Ohio in 2022. Herbicide treatments included liquid (spray‐applied) and dry (granular) formulations of flumioxazin, isoxaben + trifluralin, dimethamid‐p + pendimethalin, prodiamine + isoxaben, indaziflam, and isoxaben + dithiopyr. Treatments were applied once in Indiana and Ohio, while Florida sites received sequential applications 4 months apart. In mulched sites in Indiana and Ohio, no main effect or herbicide‐by‐formulation interaction impacted weed cover at 2 months after treatment. In bare soil at these locations, all herbicide treatments had less weed cover (35%–52%) compared to the nontreated control (98%), except dry‐applied flumioxazin (88%) and dry‐applied indaziflam (74%). In the two Florida mulched sites, liquid‐applied indaziflam and both formulations of flumioxazin and dimethenamid‐p + pendimethalin had lowest weed cover at 2 months after the second treatment (<23%). All other treatments had weed cover (30%–39%) similar to the nontreated control (39%). This research demonstrated mulching to be more effective than preemergence herbicides in Indiana and Ohio. However, preemergence herbicides are important when mulch is omitted or in mulched sites with high weed pressure. Most herbicides tested were effective with some liquid‐applied herbicides enhancing weed control.
McNally et al. (Wed,) studied this question.