Weedy rice update in Arkansas, USA, and adjacent locales

Abstract

Weedy rice (Oryza sativa L.) is among the most problematic weeds in rice (Oryza sativa L.) production. The commercialization of herbicide-resistant (HR) rice nearly two decades ago provided an effective tool to manage weedy rice; however, resistance evolution and volunteer HR hybrid rice kept weedy rice at the forefront of rice weed control needs. This research aimed to assess the prevalence and severity of weedy rice infestations, identify production practices that may have contributed to an increase in weedy rice, and identify control strategies that may still be effective on weedy rice across Arkansas and adjacent US mid-south locales. Two questionnaires, one for rice growers and consultants and one for County Extension Agents (CEAs), were distributed through e-mail and physical copies in 2020. Thirty-three respondents returned the rice grower (25) and consultant (8) survey representing 26 and seven counties in Arkansas and the Bootheel Missouri area, respectively, as well as four parishes in northeast Louisiana. Eighteen respondents returned the CEA survey. Respondents ranked weedy rice the third most problematic weed in rice, behind Echinochloa spp. and Cyperus spp. The most common infestation levels reported in 78% of fields was less than 12 m−2. Crop rotation (64% growers/consultants, 50% CEAs) and HR rice technology (27% growers/consultants, 50% CEAs) were the top-two most effective methods for weedy rice management, respectively. Tillage and crop rotation practices significantly influenced weedy rice infestation. Rice-soybean [Glycine max (L.) Merr.] rotation had the lowest weedy rice infestation compared to monoculture rice and other crop rotation practices. Crop rotation was not practiced on 26% of reported fields, primarily due to poor drainage. The imidazolinone (IMI)-resistant rice technology was still effective (>70% control) in 60% of fields, but quizalofop-resistant rice is needed to control IMI-resistant weedy rice. Overall, weedy rice remains a challenging weed in rice production.

Toxicity and selective mechanism of imazamox by weedy rice and imidazolinone‐resistant rice in China

“…Hybridization of sensitive weedy rice and IMI-resistant rice carrying the Ser653Asn substitution leads to resistance in weedy rice. Some methods have been proposed to mitigate IMI-resistant weedy rice populations, such as the introduction of Provisia ® rice resistant to aryloxyphenoxypropanoates (APP, e.g., quizalofop) and biotechnological-based strategies (Roma- Burgos et al, 2021). IMI-resistant weedy rice can be controlled using quizalofop-resistant rice technology within a short period (Burgos et al, 2008).…”

Quizalofop-resistant rice response to quizalofop when exposed to low rates of glyphosate and imazethapyr

“…Provisia rice constituted 2.7% of the total rice hectares planted in Arkansas in the growing season of 2020. However, when evaluated in commercial rice trials (Frizzell et al 2021, Hardke 2021, quizalofop-resistant rice has had lower yield potential resulting in reduced commercial adoption even though quizalofop is another tool for managing herbicide-resistant weedy rice (Roma-Burgos et al 2021). A single-point mutation confers the resistance mechanism in quizalofop-resistant rice, and the presence of the resistant ACCase allele can be detected at low cost with standard molecular biology laboratory equipment.…”

“…In addition, sublethal glyphosate rates are detrimental to rice and have been shown to cause substantial injury and yield reductions ranging from 18% to 89% when plants were exposed to a 140 g ae ha −1 (1/8× rate of labeled use rate of 1,120 g ae ha −1 ) at the 3-to 4-leaf to the booting rice stages (Kurtz and Street 2003). In Arkansas, a survey conducted in 2020 showed that glyphosate was used as a preplant option individually or in combination with protoporphyrinogen oxidase inhibitors, synthetic auxins, and diterpene biosynthesis inhibiting herbicides on 60% of total rice fields surveyed (Roma-Burgos et al 2021). Therefore, glyphosate applied preplant could potentially cause injury to nearby emerged conventional and quizalofopresistant rice fields in early rice growth stages.…”

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

“…In 2020, quizalofop‐resistant rice was grown on 39,450 and 30,740 acres, accounting for 2.7 and 6.5% of the total acreage under rice production in Arkansas and Louisiana, respectively, and is expected to increase rapidly in future growing seasons (Hardke, 2021; Harrell, 2021). Quizalofop‐resistant rice technology is needed because of the continuous evolution of herbicide‐resistant grass weeds (Roma‐Burgos et al., 2021) including problematic weeds such as barnyardgrass [ Echinochlo a crus‐galli (L.) P. Beauv.…”