Garry N. McCauley

Control of Red Rice (Oryza sativa) in Imidazolinone-Tolerant Rice (O. sativa)1

Field experiments were conducted near Beaumont, TX, to evaluate red rice control in imidazolinone-tolerant rice. Imazethapyr was applied preplant incorporated (PPI) and preemergence (PRE) at 70 and 105 g ai/ha and postemergence (POST) at 36, 52, and 70 g/ha. Single imazethapyr applications were made at each rate and timing and in sequential PPI or PRE followed by POST treatments. Red rice control ranged from 92 to 98% with sequential imazethapyr applications. Red rice control was higher when imazethapyr was applied PPI alone than PRE alone. But when these treatments were followed by a POST application of imazethapyr, there were no differences in red rice control between PPI and PRE application. Red rice control with sequential treatments was not improved with increased rates of imazethapyr POST. Visual injury to the 93AS3510 imidazolinone-tolerant variety was 5% or less 20 d after treatment (DAT), and there was no injury by 45 DAT. But POST applications of 70 g/ha imazethapyr may produce minor yield reductions to this experimental variety without improving red rice control. Results indicate that an imidazolinone-tolerant rice production system can be effective for controlling red rice and that PRE applications must be followed by a POST application to achieve maximum red rice control. PPI applications of imazethapyr at 70 g/ha should also be followed by a POST application to maximize red rice control. Nomenclature: Imazethapyr; red rice, Oryza sativa L. # ORYSA ‘93AS3510’; rice, Oryza sativa L. #3 ORYSA. Additional index words: Clearfield rice, imidazolinone-tolerant rice, Newpath, red rice control. Abbreviations: DAT, days after treatment; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Seed longevity of red rice ecotypes buried in soil

Red rice is a troublesome weed in irrigated rice production and is spread through contaminated commercial rice seed and machinery. Seed dormancy is a major trait for red rice. Studies were carried out at two locations to determine red rice seed longevity in the soil of several ecotypes from four US states. Five months after burial near Beaumont, Texas only three ecotypes had viable seed (<1%) when buried at 5 cm, but 9 ecotypes had viable seed after two years when buried at 25 cm. At the thirty-sixth month after burial, ecotypes Arkansas 2, Louisiana 2 and 4, Mississippi 4 and Texas 1 had viable seeds, but at less than 1%. Freshly harvested red rice seeds buried at 12 cm near College Station, TX, survived longer than seeds placed on the soil surface. The percentage of maximum viable seeds was 2% for blackhull type Texas 4, after 17 months. In both studies, commercial rice cultivar seeds were not viable after 5 months, regardless of their position in the soil. Under farming conditions with no fallow land preparations or deep tillage, most red rice seed germinated or was dead after 2 to 3 years, with only minor variation among ecotypes.

Imazethapyr Application Methods and Sequences for Imidazolinone-Tolerant Rice (Oryza sativa)'

Experiments were conducted at two locations in Texas during 2000 and 2001 to compare barnyardgrass, broadleaf signalgrass, and red rice control; rice tolerance; and grain yield after single and sequential applications of imazethapyr in imidazolinone-tolerant rice. Red rice and barnyardgrass control on a clay soil at Beaumont was at least 94% with imazethapyr at 70, 90, and 100 g ai/ha applied preplant incorporated (PPI) or preemergence (PRE) followed by (fb) at least 40 g/ha of imazethapyr applied early postemergence (EPOST). Broadleaf signalgrass control on a very fine sandy loam soil at Eagle Lake was at least 86% when imazethapyr was applied PPI or PRE fb EPOST applications of imazethapyr. Sequential postemergence applications at Beaumont resulted in at least 95% red rice and barnyardgrass control when 40 g/ha applied late postemergence followed any EPOST application. Sequential postemergence applications at Eagle Lake controlled broadleaf signalgrass 98% during both years. Imazethapyr applied postemergence injured rice 0 to 34% up to 12 d after treatment. Rice yield reductions were correlated to weed control and most likely were not associated with early-season rice injury. Nomenclature: Imazethapyr; imidazolinone; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; red rice, Oryza sativa L. # ORYSA; rice, Oryza sativa L. # ORYSA. Additional index words: CLEARFIELD* rice, Newpath. Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; PD, panicle differentiation; PPI, preplant incorporated; PRE, preemergence.

Imazethapyr is Safe and Effective for Imidazolinone-Tolerant Rice Grown on Coarse-Textured Soils'

A study was conducted in 2001 and 2002 in Texas to evaluate red rice control and crop response of imidazolinone-tolerant rice with imazethapyr on coarse-textured soils. Because imazethapyr was not registered for use on imidazolinone-tolerant rice on coarse-textured soils in Texas, crop response was evaluated to determine whether imidazolinone-tolerant rice yields would be reduced with sequential applications of imazethapyr on soils having greater than 50% sand content. The treatment factors consisted of preemergence (PRE) applications of imazethapyr at 50, 70, or 87 g ai/ ha followed by (fb) preflood (PREFLD) applications of 35 or 50 g/ha. Imazethapyr at 70 g/ha PRE fb 70 g/ha PREFLD was added as a seventh treatment. PRE applications were activated by rainfall or surface irrigation after application, and PREFLD applications were sprayed 1 to 2 d before application of the permanent flood. In both years, 100% red rice control was achieved with all rate combinations. Early-season visual rice injury ranged from 5 to 21% and did not result in yield losses, indicating that imazethapyr is safe on coarse-textured soils. Nomenclature: Imazethapyr; red rice, Oryza sativa L. #3 ORYSA; rice, Oryza sativa L. ‘CL121’. Abbreviations: DAT, days after treatment; fb, followed by; PRE, preemergence; PREFLD, preflood.

Effect of flood timing on red rice (Oryza spp.) control with imazethapyr applied at different dry-seeded rice growth stages

Field experiments were conducted in 2002 and 2003 in Beaumont, TX, to evaluate the effect of flood timing on red rice control with imazethapyr applied at different cultivated rice growth stages. Treatments included flood establishment at 1, 7, 14, and 21 d after postemergence (POST) herbicide treatment (DAT). Imazethapyr was applied preemergence at 70 g ai/ha followed by 70 g/ ha POST when imidazolinone-tolerant rice cultivar ‘CL-161’ had three- to four-leaf stage (EPOST) or five-leaf stage (LPOST). Flood needed to be established within 14 DAT to achieve at least 95% red rice control when imazethapyr was applied EPOST. However, flood needed to be established within 7 DAT to provide at least 95% red rice control when imazethapyr was applied LPOST. Delaying the flood up to 21 DAT reduced rice grain yield for both application timings. Nomenclature: Imazethapyr; red rice, Oryza sativa L., #ORYSA3; rice, Oryza sativa L., cultivar ‘CL-161.’ Additional index words: Acetolactate synthase (EC 4.1.3.18), ALS inhibitor, Clearfield rice, imidazolinone, water management. Abbreviations: ANOVA, analysis of variance; DAPOST, days after postemergence treatments; DAT, days after treatment; EMS, ethyl methanesulfonate; EPOST, early postemergence; LPOST, late postemergence; POST, postemergence; PRE, preemergence.

Soil characteristics and water potential effects on plant-available clomazone in rice

Abstract Clomazone has been successfully used for weed control in rice, but crop injury is a potential problem on light-textured soils. Experiments were conducted to determine the effect of soil characteristics and water potential on plant-available clomazone and rice injury. A centrifugal double-tube technique was used to determine plant-available concentration in soil solution (ACSS), total amount available in soil solution (TASS), and Kd values for clomazone on four soils at four water potentials. A rice bioassay was conducted parallel to the plant-available study to correlate biological availability to ACSS, TASS, and Kd. TASS was significantly different in all soils. The order of increasing TASS for the soils studied was Morey < Edna < Nada < Crowley, which correlated well with soil characteristics. The order of increasing TASS after equilibrium was − 90 < − 75 < − 33 < 0 kPa. TASS values at 0 kPa were greater than two times the TASS values at − 90 kPa. It appears that severe rice injury from clomazone on these soils could occur if TASS > 110 ng g−1 and Kd < 1.1 ml g−1. We propose that the double-tube technique provides a more accurate estimate of available herbicide because the solution–soil ratios are < 0.33:1 and would be more representative of a plant root–herbicide relationship. This technique or some variation possibly could be further developed such that clomazone rates could be more clearly defined particularly on lighter-textured soils. TASS may be a better predictor of plant-available herbicide than ACSS when evaluating moderately to highly water-soluble herbicides in a nonsaturated soil environment. Nomenclature: Clomazone.

Effect of Temperature and Propanil on Penoxsulam Efficacy, Absorption, and Translocation in Alligatorweed (Alternanthera philoxeroides)

Abstract Laboratory studies were conducted in 2006 and 2007 to evaluate the effects of temperature and propanil on alligatorweed control with penoxsulam. Biomass reduction of alligatorweed at 42 d after treatment (DAT) compared to nontreated was greatest at 21/11 C (day/night) compared to 26/18 C or 30/25 C for all treatments. Propanil plus penoxsulam reduced biomass less than penoxsulam applied alone, independent of temperature. At 21 and 27 C, delaying propanil application 3 d after penoxsulam provided similar biomass reduction to penoxsulam applied alone. At 27 C and 30 C, delaying propanil application 10 d after treatment was required to achieve biomass reduction greater or equal to penoxsulam applied alone. Absorption and translocation of 14C penoxsulam indicated that propanil reduced absorption of penoxsulam into the treated leaf of alligatorweed 48 h after treatment. This research demonstrates the potential for propanil to antagonize penoxsulam when applied to alligatorweed. Under the most severe antagonistic conditions (30 C) propanil applications following penoxsulam needed to be delayed 10 d to avoid antagonism. Nomenclature: Penoxsulam; propanil; alligatorweed, Alternantherea philoxeroides (Mart.) Griseb. ALRPH.

Early Postemergence Clomazone Tank Mixes on Coarse-Textured Soils in Rice

Abstract Clomazone was labeled for rice in 2001; however, that label excluded its use on coarse- (light) textured soils, including sand, loamy sand, and sandy loam with less than 1% organic matter due to rice injury. Field studies conducted in 2005, 2006, and 2007 evaluated weed control and tolerance of rice to early postemergence (EPOST) applications of clomazone alone and tank mixed with other herbicides on sandy loam and clay loam soils. At 42 d after treatment (DAT), broadleaf signalgrass (BRAPP) and barnyardgrass (ECHCG) control was > 86%. At 14 DAT, rice injury was greatest (13%) from clomazone applied preemergence (PRE) at 0.44 kg ai/ha on sandy soil. Annual sedge (CYPCP) control was > 78% on sandy loam soils at 14 DAT, but increased to > 90% by 42 DAT. On clay loam soils, CYPCP control at 42 DAT ranged from 60 to 76% from clomazone alone or tank mixed with cyhalofop or fenoxaprop. All other tank mixes provided > 80% control. Hemp sesbania (SEBEX) control was > 80% from all tank mixes. Clomazone alone provided < 77% control. Data suggest that clomazone can be used EPOST in combination with other herbicides without causing significant rice injury on sandy loam soils in Texas. Nomenclature: Clomazone; broadleaf signalgrass, Urochloa platyphylla (Griseb.) Nash; barnyardgrass, Echinochloa crus-galli L.; annual sedge, Cyperus compressus L; hemp sesbania, Sesbania herbacea (P. Mill) McVaugh; rice, Oryza sativa L

Influence of Flood Interval and Cultivar on Rice Tolerance to Penoxsulam

Studies were conducted in 2003 and 2004 over seven environments evaluating rice root growth inhibition (RGI) and foliar injury from penoxsulam at 30 and 60 g ai/ha and bispyribac-sodium at 30 g ai/ha applied to four- to five-leaf rice at three flood timings, 1, 7, and 14 d after herbicide treatment (DAT), for five rice cultivars, ‘Bengal’, ‘Cypress’, ‘Wells’, ‘Cocodrie’, and ‘XP712’. Flooding at 1 and 7 DAT resulted in greater RGI compared with flood at 14 DAT when evaluated 1 wk after flood (WAF). By 2 WAF, RGI was greater with flooding at 1 DAT compared with flooding at 7 DAT for cultivars Bengal, Cypress, and Wells. Analyzing flood timing 1 DAT, bispyribac-sodium reduced root growth of Bengal and Cypress compared with penoxsulam at 30 g/ha at 1 week after treatment (WAT). At 2 WAT, RGI for Cocodrie was higher following penoxsulam at 60 g/ha when compared with bispyribac-sodium. By 3 WAT, RGI was higher following penoxsulam at 60 g/ha when compared with penoxsulam at 30 g/ha for Cocodrie and greater than bispyribac-sodium and penoxsulam at 30 g/ha for Cypress. Foliar injury following penoxsulam at both rates was less than injury following bispyribac-sodium for all cultivars except XP712 at 1 WAT. XP712 resulted in < 5% RGI and < 6% foliar injury at each evaluation. Rice grain yield was not affected by herbicide treatment for any cultivar compared with the standard treatment of propanil plus quinclorac. Nomenclature: Bispyribac-sodium, penoxsulam, propanil, quinclorac, rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Wells’, ‘XP712’

Rice Response to Clomazone as Influenced by Application Rate, Soil Type, and Planting Date

Clomazone is an effective herbicide widely used for PRE grass control in rice. However, use of clomazone on sandy textured soils of the western Texas rice belt can cause serious rice injury. Two field experiments at three locations were conducted in 2002 and 2003 to determine the optimum rate range that maximizes barnyardgrass and broadleaf signalgrass control and minimizes rice injury across a wide variety of soil textures and planting dates. At Beaumont (silty clay loam), Eagle Lake (fine sandy loam), and Ganado (fine sandy loam), TX, PRE application of 0.34 kg ai/ha clomazone applied to rice planted in March, April, or May optimized barnyardgrass and broadleaf signalgrass control and rice yield while minimizing rice injury. Data suggest that, although injury might occur, clomazone is safe to use in rice on sandy textured soils. Nomenclature: Clomazone, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, broadleaf signalgrass, Brachiaria platyphylla BRAPP, rice, Oryza sativa L