Rice response to sublethal rates of paraquat, metribuzin, fomesafen, and cloransulam-methyl at different application timings

Abstract

Paraquat mixtures with residual herbicides before planting is a common treatment in Mississippi, and rice in proximity is susceptible to off-target movement of these applications. Four concurrent studies were conducted in Stoneville, MS, to characterize rice performance following exposure to a sub-lethal rate of paraquat, metribuzin, fomesafen, and cloransulam-methyl at different application timings. Applications were made to rice at spiking to one-leaf (VEPOST), two- to three-leaf (EPOST), three- to four-leaf (MPOST), 7 d postflood (PFLD), and panicle differentiation (PD) growth stages. Regardless of application timing, rice injury following exposure to paraquat was ≥ 45%. Delays in maturity were increased by 0.3 d d-1 following paraquat from emergence through PD. Dry weight, rough rice yield, panicle density, and germination were reduced 18.7 g, 131.5 kg ha-1, 5.6 m-2, and 0.3%, respectively, d-1 from paraquat at emergence through PD. By 28 d after treatment (DAT), metribuzin injured rice 3 to 6%, and that injury did not translate into a yield reduction. Regardless of application timing, rice injury following fomesafen ranged from 2 to 5% 28 DAT. Rice exposed to cloransulam-methyl EPOST exhibited greatest root and foliar injury 21 and 28 DAT, respectively. Additionally, yield was reduced to 6,540 kg ha-1 compared with 7,850 kg ha-1 in the nontreated when rice was exposed to cloransulam-methyl EPOST. Rice yield was negatively affected following paraquat applied any time after rice emergence. However, applications of paraquat to rice in early reproductive growth reduced rough rice yield and seed germination the greatest. Application timing is crucial in determining severity of rice injury. Early-season injury to rice following paraquat had less effect on yield compared with injury at later stages. Additionally, fields devoted to seed rice production are at risk for reduced seed germination if exposed to paraquat during early reproductive growth stages.

Impact of reduced rates of tiafenacil at vegetative growth stages on rice growth and yield

“…By 4 WAT, injury was no greater than 5%, which was similar to decreasing injury in the current study with time. Paraquat applied at 10% of the labeled rate injured spike to 1-lf and 2-to 3-lf rice 44 to 47% at 1 and 2 WAT (Lawrence et al 2021). At 4 WAT, injury at these timings was still 45 and 42%, respectively, indicating slower recovery from paraquat injury early season than tiafenacil.…”

“…Patterson et al (2023) reported that drill-seeded rice was more tolerant to application of benzobicyclon at the 4-lf or tillering growth stages than early growth stages. Lawrence et al (2021) investigated the impacts of foliar application of sublethal rates of paraquat, a non-selective contact herbicide similar to tiafenacil, and fomesafen, a PPO herbicide like tiafenacil, to rice at the spike through panicle differentiation growth stage. Fomesafen injury three DAT exceeded 11% only with a preflood application.…”

Barnyardgrass (Echinochloa crus-galli) control and rice injury with labeled herbicides following exposure to sublethal concentrations of paraquat

“…Factor A was labeled herbicide treatment and consisted of no herbicide treatment and the herbicide products listed in Table 2 applied to rice in the three- to four-leaf (MPOST) growth stage. Factor B was paraquat (Gramoxone SL; Syngenta Crop Protection, Greensboro, NC) exposure and consisted of paraquat applied at 0 and 84 g ha −1 to rice at the spiking to one-leaf (VEPOST) stage (Lawrence et al 2020a,b; 2021). Simulated off-target movement tested with constant carrier volume was used reduced herbicide rates to simulate low concentration exposure (Davis et al 2011; Ellis et al 2002; Lawrence et al 2020b; McCoy et al 2020).…”

Responses of rice genotypes to foliar-applied metribuzin

“…There is no label for metribuzin for use in rice in California. Although information regarding the effect of metribuzin application rates and timing on weed control in rice is scant, recent studies from Mississippi have indicated that metribuzin applied post rice emergence at 42 g ai ha −1 caused 36% injury by 28 d after treatment (DAT) (Lawrence et al 2021). The same study found no correlation between rice injury from metribuzin and yield reduction, dry weight reduction, maturity delays, or seed germination (Lawrence et al 2021).…”

“…Although information regarding the effect of metribuzin application rates and timing on weed control in rice is scant, recent studies from Mississippi have indicated that metribuzin applied post rice emergence at 42 g ai ha –1 caused 36% injury by 28 d after treatment (DAT) (Lawrence et al 2021). The same study found no correlation between rice injury from metribuzin and yield reduction, dry weight reduction, maturity delays, or seed germination (Lawrence et al 2021). Mahajan and Chauhan (2022) evaluated metribuzin at rates 72 and 144 g ai ha –1 and were able to reduce jungle rice [ Echinochloa colona (L.) Link] biomass by 70% and 100%, respectively, compared to the untreated control.…”