Eric P. Webster

On the Analysis of Combined Experiments

Abstract The replication of experiments over multiple environments such as locations and years is a common practice in field research. A major reason for the practice is to estimate the effects of treatments over a variety of environments. Environments are frequently classed as random effects in the model for statistical analysis, while treatments are almost always classed as fixed effects. Where environments are random and treatments are fixed, it is not always necessary to include all possible interactions between treatments and environments as random effects in the model. The rationale for decisions about the inclusion or exclusion of fixed by random effects in a mixed model is presented. Where the effects of treatments over broad populations of environments are to be estimated, it is often most appropriate to include only those fixed by random effects that reference experimental units.

Rice (Oryza sativa) and Corn (Zea mays) Response to Simulated Drift of Glyphosate and Glufosinate1

Field research was conducted during 3 yr to evaluate response of rice and corn to simulated drift rates representing 12.5, 6.3, 3.2, 1.6, and 0.8% of the usage rates of 1,120 g ai/ha glyphosate (140, 70, 35, 18, and 9 g/ha, respectively) and 420 g ai/ha glufosinate (53, 26, 13, and 4 g/ha, respectively). Early-postemergence applications were made to two- to three-leaf rice and six-leaf corn, and late-postemergence applications to rice at panicle differentiation and to corn at nine-leaf stage (1 wk before tasseling). Crop injury was generally greater for the two highest rates of both herbicides when applied early. Little to no reduction in rice or corn height was observed with glufosinate. Glyphosate consistently reduced rice plant height when the two highest rates were applied early, and heading was delayed 2 to 5 d. In 2 of 3 yr, the highest rate of glyphosate reduced rice yield 99 and 67% when applied early and 54 and 29% when applied late. Germination of rice seeds from glyphosate-treated plants was reduced in 1 of 2 yr and for only the highest rate. For glufosinate, rice yield was reduced 30% and in only one year when applied late at the highest rate. Early application of glyphosate reduced corn yield an average of 22 to 78% for the three highest rates, but only for the highest rate at the late timing (33%). Corn yield was reduced an average of 13 and 11% for the highest rate of glufosinate at the early and late timings, respectively. In greenhouse studies, five rice varieties were equally sensitive, as were five corn varieties, to reduced rates of glyphosate and glufosinate. Nomenclature: Glufosinate; glyphosate; corn, Zea mays L. ‘Asgrow 897’, ‘Dekalb 687’, ‘Mycogen 8460’, ‘Pioneer 3223’, ‘Terral 2930’; rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Jefferson’. Additional index words: Crop injury, herbicide drift, off-target movement, rice germination, rice vigor. Abbreviations: DAP, days after plating; DAT, days after treatment.

Risk assessment of the transfer of imazethapyr herbicide tolerance from Clearfield rice to red rice (Oryza sativa)

Hybridization between Clearfield rice and weedy red rice would have a direct impact on management and long-term strategies of imazethapyr technology for rice weed control. The objective of this research was to determine rates and agronomic consequences for outcrossing between Clearfield rice and red rice. Red rice populations showed extensive variation for plant height, panicle length, tillers/plant, seeds/plant, seed set and grain weight. Outcrossing was detected from all Clearfield rice cultivars (‘CL121’, ‘CL141’, ‘CL161’, and ‘CLXL8’) to red rice and was confirmed by phenotypic and DNA marker analyses. An overall outcrossing frequency of 0.17% was observed in 2002 red rice samples with a range from 0% to 0.46%. Tolerance of 2002 red rice samples to imazethapyr corresponded to levels of acetohydroxyacid synthase (AHAS) activity. A majority (94%) of the progeny from the 2002 samples segregated 3 resistant:1 susceptible for tolerance to imazethapyr, indicating that a single dominant gene from Clearfield rice was associated with tolerance in the hybrid material. The remaining samples did not segregate for tolerance, suggesting that spontaneous mutations for tolerance were present in this material before or after crossing with Clearfield rice. A four-fold increase in outcrossing frequency of 0.68% was observed in 2003 red rice samples with the highest outcrossing frequency for a single location at 3.2%. Results from this study indicate that outcrossing between Clearfield and red rice will occur rapidly at rates that warrant early-season field scouting and a crop rotation scheme to prolong usefulness of the Clearfield technology.

Acetolactate synthase-inhibiting herbicides on imidazolinone-tolerant rice

Abstract The cross-tolerance of imidazolinone-tolerant (IMI-tolerant) rice to various acetolactate synthase (ALS)-inhibiting herbicides at one and two times labeled rates was studied. The IMI-tolerant rice is cross-tolerant to imazaquin, imazapyr, nicosulfuron, pyrithiobac, thifensulfuron plus tribenuron, and triasulfuron; is partially tolerant to imazamethabenz and metsulfuron; and is susceptible to chlorimuron, flumetsulam, imazamox, imazapic, primisulfuron, and rimsulfuron. In the greenhouse, IMI-tolerant rice injury with 70 and 140 g ai ha−1 imazethapyr was 17 and 34%, respectively, 28 DAT. Both rates of imazapyr, imazaquin, rimsulfuron, nicosulfuron, thifensulfuron plus tribenuron, and pyrithiobac, and 25 g ai ha−1 triasulfuron, injured rice the same as imazethapyr. Red rice control with 70 and 140 g ha−1 imazethapyr was 97 and 98%, respectively, 28 DAT. At label and two times the label rate, all imidazolinones, nicosulfuron, and primisulfuron controlled red rice equivalent to imazethapyr. Red rice control with 28 g ai ha−1 rimsulfuron was similar to control with 70 and 140 g ha−1 imazethapyr 28 DAT. In the field, barnyardgrass control with two times the labeled rate of imazamox, imazapic, imazapyr, imazaquin, imazamethabenz, rimsulfuron, and nicosulfuron was equal or greater than control with imazethapyr 30 DAT; however, at two times the labeled rate of imazamox, imazapic, and rimsulfuron, injury was greater than imazethapyr. Of all the herbicides tested, only nicosulfuron, imazaquin, and imazapyr offer a combination of low rice injury and high red rice control compared with imazethapyr. Nomenclature: Chlorimuron; flumetsulam; imazamethabenz; imazamox; imazapic; imazapyr; imazaquin; imazethapyr; metsulfuron; nicosulfuron; primisulfuron; pyrithiobac; rimsulfuron; thifensulfuron; triasulfuron; tribenuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; red rice, Oryza sativa L. ORYSA; rice, Oryza sativa L. ‘IMI-tolerant 93AS-3510’.

Glufosinate Tank-Mix Combinations in Glufosinate-Resistant Rice (Oryza sativa)1

At 14 d after treatment (DAT), glufosinate at 0.42 kg ai/ha controlled barnyardgrass and broadleaf signalgrass 85 and 86%, respectively. Antagonism occurred for barnyardgrass control with all mixtures of glufosinate at 0.42 kg/ha. At 14 DAT, no herbicide was superior to glufosinate at either rate when applied in mixture for the control of broadleaf signalgrass. Rice flatsedge control 7 DAT was 68 and 82% with glufosinate at 0.42 and 0.84 kg/ha alone, respectively. The addition of propanil and triclopyr enhanced rice flatsedge control over that with glufosinate alone at 0.42 or 0.84 kg/ha. At 7 DAT, all herbicide mixtures increased spreading dayflower control compared with a single treatment of glufosinate at 0.42 kg/ha. By 28 DAT, spreading dayflower control was less than 80% with all treatments. Rice injury was less than 15% with all treatments. Nomenclature: Glufosinate; propanil; triclopyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; broadleaf signalgrass, Bracharia platyphylla (Griseb.) Nash # BRAPP; rice flatsedge, Cyperus iria L. # CYPCP; spreading dayflower, Commelina diffusa Burm. f. # COMDI; rice, Oryza sativa L. ‘BNGL HC-11’, ‘BNGL-62’. Additional index words: Antagonism, synergism, tank mix. Abbreviations: DAT, days after treatment; POST, postemergence.

Fenoxaprop Interactions for Barnyardgrass (Echinochloa crus-galli) Control in Rice1

A study was conducted in 2000 and 2001 to evaluate interaction of fenoxaprop with other herbicides for barnyardgrass control in rice. Changes in herbicide interaction over time were also evaluated, and herbicide combinations were ranked on the basis of compatibility. Fenoxaprop at 0.075 kg/ha plus bentazon or propanil plus molinate resulted in an additive response for barnyardgrass control at 10, 20, and 30 d after treatment (DAT); however, when the rate of fenoxaprop increased to 0.089 kg/ha, an antagonistic effect was found. Carfentrazone and halosulfuron consistently antagonized the activity of fenoxaprop at both rates on barnyardgrass. Bensulfuron at 10 and 20 DAT and triclopyr at 20 DAT were antagonistic to fenoxaprop. An increase in interaction over time was detected when fenoxaprop at 0.089 kg/ha was applied in mixture with carfentrazone at 0.04 kg/ha or halosulfuron at 0.05 kg/ha. These results indicate that propanil plus molinate and bentazon are more compatible with fenoxaprop at 0.075 kg/ha for barnyardgrass control, whereas bensulfuron, carfentrazone, halosulfuron, and triclopyr can antagonize fenoxaprop activity on barnyardgrass. Nomenclature: Bensulfuron; bentazon; carfentrazone; fenoxaprop; halosulfuron; molinate; propanil; triclopyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; rice, Oryza sativa L. ‘Cocodrie’. Additional index words: Antagonism, synergism. Abbreviations: DAT, days after treatment; NLMIXED, nonlinear mixed procedure; POST, postemergence.

Analysis of Synergistic and Antagonistic Effects of Herbicides Using Nonlinear Mixed-Model Methodology1

When herbicides are applied in mixture, and infestation by weeds is less than expected compared with when herbicides are applied alone, a synergistic effect is said to exist. The inverse response is described as being antagonistic. However, if the expected response is defined as a multiplicative, nonlinear function of the means for the herbicides when applied alone, then standard linear model methodology for tests of hypotheses does not apply directly. Consequently, nonlinear mixed-model methodology was explored using the nonlinear mixed-model procedure (PROC NLMIXED) of SAS System®. Generality of the methodology is illustrated using data from a randomized block design with repeated measures in time. Nonlinear mixed-model estimates and tests of synergistic and antagonistic effects were more sensitive in detecting significance, and PROC NLMIXED was a versatile tool for implementation. Additional index words: Least significant difference, linear mixed models, repeated measures, tank mixture. Abbreviations: DAT, days after treatment; GH, glufosinate plus mixture herbicide; GHD, glufosinate plus mixture herbicide by DAT; ML, maximum likelihood; MSE, mean square error; Rep, replication.

Potential Use of Imazethapyr Mixtures in Drill-Seeded Imidazolinone-Resistant Rice

The efficacy of imazethapyr in drill-seeded imidazolinone-resistant rice was evaluated in Louisiana in 2000 and 2001. Imazethapyr was applied preemergence (PRE), or no PRE, followed by a postemergence (POST) application of imazethapyr alone, or in a mixture with bensulfuron, bentazon plus aciflurofen, carfentrazone, halosulfuron, propanil plus molinate, triclopyr, or V-10029. Imazethapyr applied PRE followed by a POST application of imazethapyr controlled barnyardgrass equivalent to or higher than other treatments evaluated. Red rice control at 35 days after postemergence treatment (DAT) was 66 to 81% with imazethapyr applied PRE followed by any POST application, but a reduction in control was observed with a POST application of imazethapyr. Although alligatorweed control increased with POST applications, these treatments suggested only suppression. Hemp sesbania control never exceeded 10% with imazethapyr-only treatments and at 35 DAT, all POST applications, except bensulfuron, increased control above 84%. Rice yield increased with treatments receiving a PRE application of imazethapyr compared with no imazethapyr applied PRE. Nomenclature: Acifluorfen; bensulfuron; bentazon; carfentrazone; halosulfuron; imazethapyr; molinate; propanil; V-10029, sodium 2,6-bis[(4,6-dimethoxypyrimidin-2-yl)oxy]benzoate; alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. #3 ALRPH; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W. Hill # SEBEX; red rice, Oryza sativa L. # ORYSA; rice, Oryza sativa L. imidazolinone-resistant ‘93 AS-3510’ and ‘CL 121’. Additional index words: Acetolactate synthase; Clearfield rice, herbicide mixtures. Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after postemergence treatment; IR, imidazolinone-resistant; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Use of Imazethapyr in Water-Seeded Imidazolinone-Tolerant Rice (Oryza sativa)1

Abstract: A study was established to evaluate weed control and crop response of imidazolinone-tolerant (IMI-tolerant) rice in water-seeded culture with imazethapyr at 70, 105, and 140 g ai/ha at four different soil application timings with or without 70 g/ha imazethapyr postemergence (POST). Application timings included preplant incorporated (PPI), surface application prior to seeding (SURFACE), following seeding (SEED), and at pegging (PEG). The PEG treatments were applied when green leaf tissue had emerged from the seed and the root had begun to extend downward into the soil. Response of barnyardgrass, red rice, and rice injury was not affected by the addition of an imazethapyr POST application. Barnyardgrass control was above 90% at 28 d after treatment (DAT) for both years. At 42 DAT, barnyardgrass control decreased to 88% in 1998, compared with 94% control in 1999. Averaged over years, Indian jointvetch control ranged from 44 to 74% at 28 DAT and 41 to 71% at 42 DAT. Indian jointvetch control was inconsistent and lacked uniformity over all factors. Rice injury increased as application timing was delayed from PPI to PEG in 1998 at both rating dates. In 1999, injury was not observed with imazethapyr at 28 DAT, and 1% injury was observed at 42 DAT with all imazethapyr application timings. Nomenclature: Imazethapyr; Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; Indian jointvetch, Aeschynomene indica L. # AESIN; rice Oryza sativa L, ‘93 AS-3510’. Additional index words: ALS, acetolactate synthase, Clearfield rice, soil-applied herbicide. Abbreviations: ALS, acetolactate synthase (E.C. 4.1.3.18); DAT, d after POST treatment; IMI-tolerant, imidazolinone-tolerant; PEG, pegging; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SEED, following seeding; SURFACE, surface application prior to seeding.

Imazethapyr at Different Rates and Timings in Drill- and Water-Seeded Imidazolinone-Tolerant Rice

Imazethapyr applied to the soil at 0, 35, 53, 70, 87, 105, and 140 g ai/ha followed by (fb) early-postemergence (EPOST) or late-postemergence (LPOST) applications at 140, 105, 87, 70, 53, 35, and 0 g ai/ha, respectively, was evaluated for weed control, crop tolerance, and grain yield in imidazolinone-tolerant rice. In drill- and water-seeded rice, imazethapyr effectively controlled barnyardgrass 91 to 97% with a soil fb EPOST or LPOST application except when applied at 105 fb 35 g/ha EPOST at 49 d after late-postemergence treatment. Rice yields were 5,920 and 3,920 kg/ ha in the drill-seeded study with a single application of imazethapyr at 140 g/ha EPOST in 2000 and 2001, respectively. These yields were greater than or equal to those from treatments with two imazethapyr applications. Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv #3 ECHCG; rice, Oryza sativa L. ‘93 AS-3510’, ‘CL 141’. Additional index words: Acetolactate synthase, ALS, Clearfield rice. Abbreviations: DAT, days after late-postemergence treatment; EPOST, early postemergence; fb, followed by; IT, imidazolinone tolerant; LPOST, late postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SURF, surface.