Jason A. Bond

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.

Multiple Resistance to Glyphosate and Pyrithiobac in Palmer Amaranth (Amaranthus palmeri) from Mississippi and Response to Flumiclorac

Abstract Greenhouse and laboratory studies were conducted to confirm and quantify glyphosate resistance, quantify pyrithiobac resistance, and investigate interaction between flumiclorac and glyphosate mixtures on control of Palmer amaranth from Mississippi. The GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for two glyphosate-resistant biotypes, C1B1 and T4B1, and a glyphosate-susceptible (GS) biotype were 1.52, 1.3, and 0.09 kg ae ha−1 glyphosate, respectively. This indicated that the C1B1 and T4B1 biotypes were 17- and 14-fold resistant to glyphosate, respectively, compared with the GS biotype. The C1B1 and T4B1 biotypes were also resistant to pyrithiobac, an acetolactate synthase (ALS) inhibitor, with GR50 values of 0.06 and 0.07 kg ai ha−1, respectively. This indicated that the C1B1 and T4B1 biotypes were 7- and 8-fold, respectively, more resistant to pyrithiobac compared with the GS biotype, which had a GR50 value of 0.009 kg ha−1. Flumiclorac was antagonistic to glyphosate by reducing glyphosate translocation. The C1B1 and T4B1 absorbed less glyphosate 48 h after treatment (HAT) compared with the GS biotype. The majority of the translocated glyphosate accumulated in the shoot above the treated leaf (that contains the apical meristem) in the GS biotype and in the shoot below the treated leaf in the resistant biotypes, C1B1 and T4B1, by 48 HAT. The C1B1 biotype accumulated negligible shikimate levels, whereas the T4B1 and GS biotypes recorded elevated levels of shikimate. Metabolism of glyphosate to aminomethylphosphonic acid was not detected in either of the resistant biotypes or the susceptible GS biotype. The above results confirm multiple resistance to glyphosate and pyrithiobac in Palmer amaranth biotypes from Mississippi and indicate that resistance to glyphosate is partly due to reduced absorption and translocation of glyphosate. Nomenclature: Flumiclorac; glyphosate; pyrithiobac; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA.

EPSPS amplification in glyphosate-resistant spiny amaranth (Amaranthus spinosus): a case of gene transfer via interspecific hybridization from glyphosate-resistant Palmer amaranth (Amaranthus palmeri).

BACKGROUND Amaranthus spinosus, a common weed of pastures, is a close relative of Amaranthus palmeri, a problematic agricultural weed with widespread glyphosate resistance. These two species have been known to hybridize, allowing for transfer of glyphosate resistance. Glyphosate-resistant A. spinosus was recently suspected in a cotton field in Mississippi. RESULTS Glyphosate-resistant A. spinosus biotypes exhibited a fivefold increase in resistance compared with a glyphosate-susceptible biotype. EPSPS was amplified 33-37 times and expressed 37 times more in glyphosate-resistant A. spinosus biotypes than in a susceptible biotype. The EPSPS sequence in resistant A. spinosus plants was identical to the EPSPS in glyphosate-resistant A. palmeri, but differed at 29 nucleotides from the EPSPS in susceptible A. spinosus plants. PCR analysis revealed similarities between the glyphosate-resistant A. palmeri amplicon and glyphosate-resistant A. spinosus. CONCLUSIONS Glyphosate resistance in A. spinosus is caused by amplification of the EPSPS gene. Evidence suggests that part of the EPSPS amplicon from resistant A. palmeri is present in glyphosate-resistant A. spinosus. This is likely due to a hybridization event between A. spinosus and glyphosate-resistant A. palmeri somewhere in the lineage of the glyphosate-resistant A. spinosus plants. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Response of Palmer Amaranth (Amaranthus palmeri) Accessions to Glyphosate, Fomesafen, and Pyrithiobac'

Field studies were conducted at Fayetteville, Arkansas, to determine whether 47 Palmer amaranth accessions from different areas of the southern United States varied in response to postemergence applications of the registered rates of the isopropylamine salt of glyphosate (840 g ae/ha), fomesafen (420 g ai/ha), and pyrithiobac (70 g ai/ha). Glyphosate controlled all Palmer amaranth accessions at least 99% 21 d after treatment (DAT). Palmer amaranth control with fomesafen was equivalent for all accessions and at least 96% 21 DAT. Percent dry weight reductions were at least 92 and 94% for glyphosate and fomesafen, respectively. Palmer amaranth control with pyrithiobac was variable and ranged from 20 to 94% 21 DAT, but differences could not be attributed to accession origin. Herbicides with alternate modes of action from pyrithiobac should be utilized for Palmer amaranth control in regions where pyrithiobac has been used continuously. Nomenclature: Fomesafen, glyphosate, pyrithiobac, Palmer amaranth, Amaranthus palmeri (S.) Wats. #3 AMAPA. Additional index words: Accession, dry weight reductions, ecotype, herbicide response variability. Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAE, days after emergence; DAT, days after treatment.

Weed Management Practices and Needs in Arkansas and Mississippi Rice

Abstract Crop consultants in Arkansas and Mississippi were sent a direct-mail survey in fall of 2011 with questions concerning weed management in rice. The goal of the survey was to document the extent of imidazoline-resistant rice hectares, the herbicides most commonly recommended in rice, the weeds perceived to be most troublesome in rice including those resistant to herbicides, and suggested areas of research and educational focus that would improve weed management in rice. When appropriate, results from this survey were compared to a similar survey conducted in 2006. Completed rice surveys were returned by 43 consultants, accounting for 179,500 ha of scouted rice or 38% of the rice hectarage in Arkansas and Mississippi. Imidazolinone-resistant rice was grown on 64% of the hectares, and this technology was used continually for the past 5 yr on 11% of the rice hectares. Of the area planted to imidazolinone-resistant rice, 42% of this hectarage was treated solely with an acetolactate synthase (ALS)-inhibiting herbicide. Consultants listed improved control options for barnyardgrass and Palmer amaranth as the most important research and educational need in rice. The top five weeds in order of importance were (1) barnyardgrass, (2) sprangletops, (3) red rice, (4) northern jointvetch, and (5) Palmer amaranth. From a predetermined list of research and educational topics, consultants gave the highest ratings of importance to (1) control of herbicide-resistant weeds, (2) strategies to reduce the occurrence and spread of herbicide-resistant weeds, and (3) development of new economical herbicide-resistant rice varieties which was comparable to economical weed control options. Findings from this survey point to the overuse of imidazolinone-resistant rice and a lack of preemptive resistance management strategies such as crop rotation and use of multiple effective herbicide modes of action by some growers, which has likely contributed to selection for the ALS-resistant barnyardgrass and rice flatsedge recently confirmed in Arkansas and Mississippi rice. Nomenclature: Barnyardgrass; Echinochloa crus-galli (L.) Beauv.; northern jointvetch; Aeschynomene virginica (L.) B.S.P.; Palmer amaranth; Amaranthus palmeri S. Wats.; red rice; Oryza sativa L.; rice; Oryza sativa L.; rice flatsedge; Cyperus iria L.; sprangletops; Leptochloa spp. Resumen Se envió una encuesta vía correo electrónico a asesores agrícolas en Arkansas y Mississippi en el otoño de 2011 con preguntas relacionadas al manejo de malezas en arroz. El objetivo de la encuesta fue documentar la extensión de hectáreas de arroz resistente a herbicidas imidazolinone, los herbicidas más comúnmente recomendados en arroz, las malezas percibidas como las más problemáticas en arroz incluyendo aquellas resistentes a herbicidas, y las áreas sugeridas para hacer énfasis en investigación y educación que mejorarían el manejo de malezas en arroz. Cuando fue apropiado, los resultados de esta encuesta fueron comparados con una encuesta similar realizada en 2006. Las encuestas contestadas fueron devueltas por 43 asesores, contabilizando 179,500 ha de arroz evaluado o 38% del área de arroz en Arkansas y Mississippi. Arroz resistente a imidazolinone fue sembrado en 64% de las hectáreas, y esta tecnología fue usada continuamente durante los últimos 5 años en 11% de las hectáreas de arroz. Del área sembrada con arroz resistente a imidazolinone, 42% de esta área fue tratada solamente con un herbicida inhibidor de acetolactate synthase (ALS). Los asesores mencionaron mejores opciones de control de Echinochloa crus-galli y Amaranthus palmeri como las necesidades de investigación y de educación más importantes en arroz. Las cinco malezas más importantes fueron (1) E. crus-galli, (2) Leptochloa spp., (3) arroz rojo, (4) Aeschynomene virginica, y (5) A. palmeri. A partir de una lista predeterminada de temas de investigación y educación, los asesores dieron los mayores valores según la importancia a (1) el control de malezas resistentes a herbicidas, (2) las estrategias para reducir la ocurrencia y diseminación de malezas resistentes a herbicidas, y (3) el desarrollo de nuevas variedades económicas de arroz con resistencia a herbicidas, la cuales deberían ser comparables a otras opciones de control de malezas económicas. Los resultados de esta encuesta apuntan el sobreuso de arroz resistente a imidazolinone y a la falta de estrategias de manejo preventivo de resistencia, tales como la rotación de cultivos y el uso de múltiples modos de acción de herbicidas efectivos por algunos productores, lo que probablemente ha contribuido a la selección de E. crus-galli y Cyperus iria resistentes a herbicidas ALS, las cuales fueron confirmadas recientemente en arroz en Arkansas y Mississippi.

Physiological and Molecular Basis of Acetolactate Synthase- Inhibiting Herbicide Resistance in Barnyardgrass (Echinochloa crus- galli)

Barnyardgrass biotypes from Arkansas (AR1 and AR2) and Mississippi (MS1) have evolved cross-resistance to imazamox, imazethapyr, and penoxsulam. Additionally, AR1 and MS1 have evolved cross-resistance to bispyribac-sodium. Studies were conducted to determine if resistance to acetolactate synthase (ALS)-inhibiting herbicides in these biotypes is target-site or non-target-site based. Sequencing and analysis of a 1701 base pair ALS coding sequence revealed Ala₁₂₂ to Val and Ala₁₂₂ to Thr substitutions in AR1 and AR2, respectively. The imazamox concentrations required for 50% inhibition of ALS enzyme activity in vitro of AR1 and AR2 were 2.0 and 5.8 times, respectively, greater than the susceptible biotype. Absorption of ¹⁴C-bispyribac-sodium, -imazamox, and -penoxsulam was similar in all biotypes. ¹⁴C-Penoxsulam translocation out of the treated leaf (≤2%) was similar among all biotypes. ¹⁴C-Bispyribac-treated AR1 and MS1 translocated 31- 43% less radioactivity to aboveground tissue below the treated leaf compared to the susceptible biotype. ¹⁴C-Imazamox-treated AR1 plants translocated 39% less radioactivity above the treated leaf and aboveground tissue below the treated leaf, and MS1 translocated 54 and 18% less radioactivity to aboveground tissue above and below the treated leaf, respectively, compared to the susceptible biotype. Phosphorimaging results further corroborated the above results. This study shows that altered target site is a mechanism of resistance to imazamox in AR2 and probably in AR1. Additionally, reduced translocation, which may be a result of metabolism, could contribute to imazamox and bispyribac-sodium resistance in AR1 and MS1.

Effects of Cultivars and Fungicides on Rice Sheath Blight, Yield, and Quality

The development of sheath blight (Rhizoctonia solani)-resistant rice (Oryza sativa) cultivars will allow producers to use less fungicide and to avoid significant reductions in grain and milling yields. Among cultivars currently in cultivation in the southern United States rice-producing region, sheath blight resistance levels range from very susceptible to moderately susceptible. A study was conducted to determine the response of cultivars with different levels of susceptibility to sheath blight inoculations and fungicide applications and to determine the impact of sheath blight disease development on rice yield and quality. Sheath blight epidemics in field plots were initiated by inoculation at the panicle differentiation growth stage from 2003 through 2005. Azoxystrobin at 0.17 kg a.i. ha-1 and flutolanil at 0.56 kg a.i. ha-1 were applied in sequential applications at midboot and 50 to 70% heading. Inoculation significantly increased sheath blight severity and incidence and caused yield losses of 4% in moderately susceptible cv. Francis to 21% in very susceptible cv. Cocodrie. Milling yield was affected to a lesser extent. Fungicide treatments reduced sheath blight incidence and severity regardless of cultivar. Azoxystrobin was more effective than flutolanil in minimizing yield loss due to sheath blight in all cultivars except Francis.

Comparative growth of Palmer amaranth (Amaranthus palmeri) accessions

Abstract A 2-yr field study was conducted to compare growth characteristics of 24 Palmer amaranth accessions collected from across the indigenous range of the species in the United States. Variation in growth and development of Palmer amaranth was noted among accessions based on leaf area ratio (LAR), specific leaf area (SLA), net assimilation rate (NAR), and stem leaf ratio (SLR), but only SLR varied across harvest intervals among accessions. Accessions collected across the range of Palmer amaranth in the United States displayed variation in growth and development based on differences in LAR, SLA, NAR, and SLR. Observed differences among accessions indicate the existence of Palmer amaranth ecotypes. Nomenclature: Palmer amaranth, Amaranthus palmeri (S.) Wats., AMAPA.

Adoption of Best Management Practices for Herbicide-Resistant Weeds in Midsouthern United States Cotton, Rice, and Soybean

Abstract In fall 2011, cotton and soybean consultants from Arkansas, Louisiana, Mississippi, and Tennessee were surveyed through direct mail and on-farm visits, and rice consultants from Arkansas and Mississippi were surveyed through direct mail to assess the importance and level of implementation of herbicide resistance best management practices (HR-BMPs) for herbicide-resistant weeds. Proper herbicide timing, clean start with no weeds at planting, application of multiple effective herbicide modes of action, use of full labeled herbicide rates, and prevention of crop weed seed production with importance rating of ≥ 4.6 out of 5.0 were perceived as the most important HR-BMPs in all crops. Purchase of certified rice seed was on 90% of scouted hectares. In contrast, least important HR-BMPs as perceived by consultants with importance ratings of ≤ 4.0 in cotton, ≤ 3.7 in rice, and ≤ 3.8 in soybean were cultural practices such as manual removal of weeds; tillage including disking, cultivation, or deep tillage; narrow (≤ 50 cm)-row crops, cover crops, and altered planting dates. Narrow crop rows and cover crops in cotton; altered planting dates in cotton and soybean; and cleaning of farm equipment and manual weeding in rice and soybean is currently employed on ≤ 20% of scouted hectares. Extra costs, time constraints, adverse weather conditions, lack of labor and equipment, profitability, herbicide-related concerns, and complacency were perceived as key obstacles for adoption of most HR-BMPs. With limited adoption of most cultural practices that reduce risks of herbicide-resistant weeds, there are opportunities to educate growers concerning the proactive need and long-term benefits of adopting HR-BMPs to ensure sustainable weed management and profitable crop production. Nomenclature: Cotton; Gossypium hirsutum L.; rice; Oryza sativa L.; soybean; Glycine max (L.) Merr. Resumen En el otoño de 2011, se encuestó a asesores para la producción de algodón y soya de Arkansas, Louisiana, Mississippi, y Tennessee mediante correo directo o visitas en finca, y a asesores de producción de arroz de Arkansas y Mississippi mediante correo directo, para evaluar la importancia y el nivel de implementación de las mejores prácticas de manejo de resistencia a herbicidas (HR-BMPs) para el manejo de malezas resistentes a herbicidas. El momento apropiado de aplicación del herbicida, la siembra en condiciones libres de malezas, la aplicación de múltiples herbicidas efectivos con diferentes modos de acción, el uso de la dosis alta del herbicida, y la prevención de producción de semilla de malezas dentro del cultivo fueron percibidas como las HR-BMPs más importantes en todos los cultivos con niveles de importancia ≥4.6 de 5.0. La compra de semilla certificada de arroz estuvo presente en 90% de las hectáreas evaluadas. En cambio, las HR-BMPs menos importantes según la percepción de los asesores con niveles de importancia ≤4.0 en algodón, ≤3.7 en arroz, y ≤3.8 en soya fueron prácticas culturales tales como la deshierba manual, la labranza con discos, el cultivo, o la labranza profunda, el uso de distancias de siembra reducidas entre hileras (≤50 cm), uso de coberturas vivas, y modificación de fechas de siembra. El uso de distancias reducidas entre hileras y de coberturas vivas en algodón, la modificación de fechas de siembra en algodón y soya, y la limpieza de equipo agrícola y la deshierba manual en arroz y soya son utilizados actualmente en ≤20% de las hectáreas evaluadas. Costos extra, limitaciones en disponibilidad de tiempo, condiciones climáticas adversas, falta de mano de obra y equipo, rentabilidad, preocupaciones relacionadas a los herbicidas, y la complacencia fueron percibidos como los principales obstáculos para la adopción de la mayoría de las HR-BMPs. La limitada adopción de la mayoría de las prácticas culturales para reducir los riesgos de las malezas resistentes a herbicidas, indican que existen oportunidades para educar a los productores sobre la necesidad y los beneficios en el largo plazo de adoptar HR-BMPs para asegurar el manejo sostenible de malezas y la rentabilidad de la producción.

Evaluation of Mesotrione in Mississippi Delta Corn Production1

Field studies were conducted in Arkansas in 1999, 2000, and 2001 to evaluate mesotrione applied preemergence (PRE) and postemergence (POST) for weed control in corn grown in the Mississippi Delta region of the United States. Mesotrione was applied PRE (140, 210, and 280 g/ ha) alone and POST (70, 105, and 140 g/ha), alone or in tank mixtures with atrazine (280 g/ha). Standard treatments for comparison were S-metolachlor/atrazine PRE and S-metolachlor plus atrazine PRE followed by atrazine POST. All PRE treatments controlled velvetleaf, pitted morningglory, entireleaf morningglory, prickly sida, and broadleaf signalgrass 95% 2 wk after emergence (WAE). Mesotrione controlled velvetleaf 89% or more 4 and 6 WAE. Control of morningglory species by mesotrione POST averaged 92% 6 WAE. Prickly sida was controlled at least 90% by all treatments 4 WAE. Mesotrione applied alone PRE and POST controlled broadleaf signalgrass 83 to 91% 4 WAE. All treatments controlled broadleaf signalgrass less than 90% 6 WAE, except treatments that contained S-metolachlor, which gave 94% or greater control. Corn yield ranged from 10.5 to 12.4 Mg/ha and did not differ among treatments. Mesotrione PRE and POST provided excellent control of broadleaf weeds, but S-metolachlor was needed for broadleaf signalgrass control. Nomenclature: Atrazine; mesotrione; S-metolachlor; broadleaf signalgrass, Brachiaria platyphylla Griseb. Nash #3 BRAPP; entireleaf morningglory, Ipomoea hederacea var. integriuscula L. Jacq. # IPOHG; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; velvetleaf, Abutilon theophrasti Medicus. # ABUTH; corn, Zea mays L. ‘Pioneer YieldGuard 31B13’. Additional index words: HPPD-inhibiting herbicides, triketone herbicides. Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; WAE, weeks after emergence; WAP, weeks after planting; WAT, weeks after treatment.