Rice safety and control of penoxsulam-resistant and -susceptible barnyardgrass (Echinochloa crus-galli) populations with soil-applied herbicides

Resistance to penoxsulam among barnyardgrass populations is prevalent in rice fields in China. Seeds of penoxsulam-resistant (AXXZ-2) and penoxsulam-susceptible (JLGY-3) barnyardgrass populations, as well as the seeds of two rice varieties, including Wuyungeng32 (WY) and Liangyou669 (LY), were planted in plastic pots and then treated with a rate titration of acetochlor, anilofos, butachlor, clomazone, oxadiazon, pendimethalin, pretilachlor, pyraclonil, or thiobencarb. The two barnyardgrass populations exhibited similar susceptibility to acetochlor, anilofos, butachlor, oxadiazon, pretilachlor, or pyraclonil. However, the susceptibility differed between the barnyardgrass populations in response to clomazone, pendimethalin, and thiobencarb. For AXXZ-2, herbicide rates that caused 50% reduction in shoot biomass from the nontreated control (GR₅₀) were 179, >800, and 1,798 g ha⁻¹ for clomazone, pendimethalin, and thiobencarb, respectively; whereas JLGY-3 GR₅₀ values were 61, 166, and 552 g ha⁻¹, respectively. Both rice varieties demonstrated excellent tolerance to acetochlor, butachlor, oxadiazon, pretilachlor, and thiobencarb. However, substantial rice damage was observed when anilofos and clomazone were used. Anilofos at 352 g ha⁻¹ and clomazone at 448 g ha⁻¹ reduced rice shoot biomass by 41% and 50% from the nontreated, respectively. Averaged across herbicide rates, clomazone use resulted in a reduction in rice shoot biomass from that of the nontreated control by 52% and 34% for WY and LY, respectively; and pendimethalin use resulted in a reduction in rice shoot biomass from the nontreated control by 25% and 9% for WY and LY, respectively. Nomenclature: acetochlor; anilofos; butachlor; clomazone; oxadiazon; pendimethalin; pretilachlor; pyraclonil; thiobencarb; barnyardgrass; Echinochloa crus-galli (L.) Beauv.; rice; Oryza sativa L.