Effects of early season soil moisture and nitrogen applications on tolerance of quizalofop‐resistant rice to quizalofop

Abstract

AbstractQuizalofop‐resistant rice (Oryza sativa L.) allows for postemergence applications of quizalofop. Previous research reported that soil moisture availability strongly influences the response of grass species to aryloxyphenoxypropionate herbicides. Experiments were conducted at Stuttgart, AR, and at Colt, AR, in 2021 to investigate the influence of early season soil moisture and nitrogen (N) applications on the tolerance of quizalofop‐resistant cultivars to sequential quizalofop applications. The experiment was implemented as a two‐factor, randomized complete block design. The factors evaluated were cultivar (PVL02 and RTv7231 MA) and herbicide treatment (nontreated control; nontreated control fertilized with ammonium sulfate [AMS] at 100 lb acre−1 and surface irrigated at the two‐leaf stage; sequential quizalofop applications at 1× and 2× rates; sequential quizalofop at 1× and 2× rates surface irrigated at the two‐leaf stage; and sequential quizalofop applications at 1× and 2× rates fertilized with AMS at 100 lb acre−1 then surface irrigated at the two‐leaf stage). Sequential quizalofop applications were applied at the two‐leaf and five‐leaf stages, with 1× and 2× rates of quizalofop being 0.11 and 0.22 lb a.i. acre−1, respectively. RTv7231 MA injury was 2‐ to6‐percentage points higher than PVL02 at all visual injury ratings averaged across treatment and location. Sequential quizalofop applications caused 1–9% visible injury to quizalofop‐resistant cultivars pooled over locations and rating timings. Growers could consider environmental conditions before herbicide applications to mitigate the risk of injury to quizalofop‐resistant cultivars from quizalofop, and drier soil conditions could be used for quizalofop applications onto rice compared with saturated soil conditions.