Seedbank management through an integration of harvest-time and postharvest tactics for Italian ryegrass (Lolium perenne ssp. multiflorum) in wheat

Italian ryegrass is a major weed in winter cereals in the south-central United States. Harvest weed seed control (HWSC) tactics that aim to remove weed seed from crop fields are a potential avenue to reduce Italian ryegrass seedbank inputs. To this effect, a 4-yr, large-plot field study was conducted in College Station, Texas, and Newport, Arkansas, from 2016 to 2019. The treatments were arranged in a split-plot design. The main-plot treatments were (1) no narrowwindrow burning (a HWSC strategy) + disk tillage immediately after harvest, (2) HWSC disk tillage immediately after harvest, and (3) HWSC + disk tillage 1 mo after harvest. The subplot treatments were (1) pendimethalin (1,065 g ai ha(-1); Prowl H2O (R)) as a delayed preemergence application (herbicide program #1), and (2) a premix of flufenacet (305 g ai ha(-1)) + metribuzin (76 g ai ha(-1); Axioms) mixed with pyroxasulfone (89 g ai ha(-1); Zidua (R) WG) as an early postemergence application followed by pinoxaden (59 g ai ha(-1); Axial (R) XL) in spring (herbicide program #2). After 4 yr, HWSC alone was significantly better than no HWSC. Herbicide program #2 was superior to herbicide program #1. Herbicide program #2 combined with HWSC was the most effective treatment. The combination of herbicide program #1 and standard harvest practice (no HWSC; check) led to an increase in fall Italian ryegrass densities from 4 plants m(-2) in 2017 to 58 plants m(-2) in 2019 at College Station. At wheat harvest, Italian ryegrass densities were 58 and 59 shoots m(-2) in check plots at College Station and Newport, respectively, whereas the densities were near zero in plots with herbicide program #2 and HWSC at both locations. These results will be useful for developing an improved Italian ryegrass management strategy in this region.