AbstractMesotrione (2‐[4‐(methylsulfonyl)‐2‐nitrobenzoyl]‐1,3‐cyclohexanedione) is a proven effective weed control product in agricultural and turf settings but its use within a hydroseeding mixture has not been investigated. Two experiments were conducted to evaluate the effects of (1) mesotrione rate and (2) duration of herbicide exposure on turf establishment and weed populations through hydroseeding establishment methodology. The experimental design of both studies was a randomized complete block, incorporating a split‐plot in the second study, with four replications and repeated in two years. Perennial ryegrass (Lolium perenne L., variety not stated) was hydroseeded on a silt loam soil (pH 7.0) in summer at 39 g m−2 in a slurry delivering 6.1 L m−2. Treatments in the first study were mesotrione rates of 0.000, 0.088, 0.175, and 0.263 kg a.i. ha−1. Treatments in the second study were duration of mixture in tank before applying of 0, 2, and 4 h, with and without mesotrione at 0.175 kg a.i. ha−1. Turfgrass percent cover, turfgrass injury, and weed populations were assessed for both studies. The addition of mesotrione at any rate to the hydroseeding slurry did not reduce desired turf populations; in many cases, the amount of desired turf cover increased. Weed populations were significantly reduced by all mesotrione rates; the effect was most evident at the two highest rates. No treatments caused turf injury. Length of time in the hydroseeding slurry did not reduce herbicide efficacy or desired turf populations, or cause turf injury.