Weed control and water-seeded rice response to pyraclonil applied at different timings and in herbicide combinations

Pyraclonil is a new herbicide to control weeds in California water-seeded rice (Oryza sativa L.). The objectives of this research were to evaluate weed control and rice response from pyraclonil applied alone at different timings and when applied in combinations with other herbicides. In one field study, pyaclonil was applied at 0.3 lbs a.i. ac⁻¹ on pre-seed bare ground, 1-inch flood, 4-inch flood and 3 days after flooding in water-seeded rice. In another study, pyraclonil was applied at 0.3 lbs a.i. ac⁻¹ at day of rice seeding and followed by various registered herbicides. Pyraclonil applications resulted in similar weed control across timings. Pyraclonil provided greater than 92% control of smallflower umbrella sedge (Cyperus difformis L.) and broadleaf weeds but less than 60% control of ricefield bulrush [Schoenoplectus mucronatus (L.) Palla] at 42 days after treatment. Watergrass (Echinochloa spp.) control was achieved with pyraclonil if applied before emergence. Early-season rice injury from pyraclonil was observed; however, rice appeared uninjured later in the season. The addition of other herbicides after a pyraclonil application increased weed control levels across weed species and resulted in grain yields from 6,925 to 8,623 and 9,182 to 10,865 lbs ac⁻¹ in 2019 and 2021, respectively. Pyraclonil provides early-season weed control and, when incorporated with other herbicides, will be a useful herbicide in water-seeded rice.