Joseph L. Matthews

Effect of Postemergence Application Rate and Timing of Mesotrione on Corn (Zea mays) Response and Weed Control1

Field experiments were conducted in 1999 and 2000 to determine the influence of mesotrione postemergence application rate, application timing, and addition of atrazine on corn injury, weed control, and corn grain yield. Corn injury in the form of leaf bleaching ranged from 0 to 15% at 7 d after treatment (DAT). In general, most of the bleaching injury rapidly dissipated with slight (≤ 8%) to no corn injury observed at 28 DAT. Control of common cocklebur with mesotrione at 14 DAT ranged from 79 to 98% for all treatments over both years. Applying mesotrione at 140 g/ha, at the early postemergence (EPOST) timing, or in combination with atrazine provided the greatest control of common cocklebur at 14 DAT. Application rate of mesotrione was the only factor that was significant in both years for control of common cocklebur later in the season at 56 DAT. Control of ivyleaf morningglory with mesostrione at 14 DAT ranged from 60 to 90% for all treatments in both years. Control of ivyleaf morningglory at 14 DAT was enhanced by the addition of atrazine to mesotrione. Control of ivyleaf morningglory at 56 DAT was greater with mid-postemergence and late postemergence than with EPOST applications, and was generally enhanced by the addition of atrazine. Yellow nutsedge control with mesotrione was inconsistent, ranging from 40 to 87% at 14 DAT for all treatments over both years. The addition of atrazine to mesotrione increased yellow nutsedge control from 47 to 87% at 14 DAT in 2000. Increasing the rate of mesotrione from 70 to 140 g/ha, as well as the addition of atrazine, improved control of yellow nutsedge at 56 DAT. Corn grain yield was not affected by corn injury or weed control as there were no significant differences in grain yield between herbicide-treated plots and handweeded plots. Nomenclature: Atrazine; mesotrione; common cocklebur, Xanthium strumarium L. #3 XANST; ivyleaf morningglory, Ipomoea hederacea L. Jacq. # IPOHE; yellow nutsedge, Cyperus esculentus L. # CYPES; corn Zea mays L. ‘DK 592SR’, ‘DK 683SR’. Abbreviations: COC, crop-oil concentrate; DAT, days after treatment; EPOST, early postemergence; MPOST, mid-postemergence; LPOST, late postemergence; PRE, preemergence; UAN, 28% urea ammonium nitrate.

Winter Annual Weed Control with Fall-Applied Corn (Zea mays) Herbicides1

Field studies were conducted during the 2000 to 2001 growing seasons to evaluate winter annual weed control and crop tolerance with fall-applied herbicides in corn at Belleville, IL. Atrazine, simazine, and rimsulfuron plus thifensulfuron applied in the fall controlled mouseear chickweed, henbit, and Carolina foxtail 93% or greater at planting the following spring. Flumetsulam controlled mouseear chickweed and henbit 98 and 93%, respectively, at planting. Metribuzin controlled mouseear chickweed and henbit 100 and 97%, respectively. CGA-152005 controlled mouseear chickweed, henbit, and wild garlic 93 to 100%. CGA-152005 provided the greatest control of wild garlic, with control ranging from 94 to 100% at planting. CGA-152005 plus simazine controlled 99 to 100% of all winter annual weeds evaluated. Reducing winter annual weed vegetation did not increase soil temperatures at 5-cm depth in May. CGA-152005 caused discoloration and height reduction of corn. CGA-152005 at the highest rate (60 g ai/ha) reduced corn plant height by 7% and grain yield by 8%. Nomenclature: Atrazine; CGA-152005, 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]]-urea; flumetsulam; metribuzin; rimsulfuron; simazine; thifensulfuron; Carolina foxtail, Alopercurus carolinianus Walt. #3 ALOCA; henbit, Lamium amplexicaule L. # LAMAM; mouseear chickweed, Cerastium vulgatum L. # CERVU; wild garlic, Allium vineale L. # ALLVI; corn, Zea mays (L.) ‘Pioneer 33G28 LL’. Additional index words: Discoloration, height reduction, preemergence. Abbreviations: DAP, days after planting; DAT, days after treatment; POST, postemergence.

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 4: Weed management practices and effects on weed populations and soil seedbanks †

BACKGROUND Weed management in glyphosate-resistant (GR) maize, cotton and soybean in the United States relies almost exclusively on glyphosate, which raises criticism for facilitating shifts in weed populations. In 2006, the benchmark study, a field-scale investigation, was initiated in three different GR cropping systems to characterize academic recommendations for weed management and to determine the level to which these recommendations would reduce weed population shifts. RESULTS A majority of growers used glyphosate as the only herbicide for weed management, as opposed to 98% of the academic recommendations implementing at least two herbicide active ingredients and modes of action. The additional herbicides were applied with glyphosate and as soil residual treatments. The greater herbicide diversity with academic recommendations reduced weed population densities before and after post-emergence herbicide applications in 2006 and 2007, particularly in continuous GR crops. CONCLUSION Diversifying herbicides reduces weed population densities and lowers the risk of weed population shifts and the associated potential for the evolution of glyphosate-resistant weeds in continuous GR crops. Altered weed management practices (e.g. herbicides or tillage) enabled by rotating crops, whether GR or non-GR, improves weed management and thus minimizes the effectiveness of only using chemical tactics to mitigate weed population shifts.

Influence of Weed Competition and Herbicides on Glyphosate-Resistant Soybean (Glycine max)1

Abstract: Field studies were conducted from 1997 to 1999 to evaluate the influence of weed competition and herbicides on glyphosate-resistant soybean at the Belleville Research Center at Belleville, IL. Season-long weed competition did not delay maturity or reduce soybean population. However, season-long weed competition reduced soybean height by 10% and grain yield by 68%. Competition from weeds 30 cm in height or less did not increase days to maturity or reduce plant population, height, or grain yield. Chlorimuron plus thifensulfuron caused 6% height reduction at 21 d after treatment. Despite the injury from herbicides, none increased days to maturity or reduced plant height, population, or grain yield of soybean. The soil-applied herbicides alachlor, imazaquin, and pendimethalin and the postemergence herbicides acifluorfen, bentazon, chlorimuron, imazethapyr, and thifensulfuron did not reduce yield of glyphosate-resistant soybean. Nomenclature: Acifluorfen; alachlor; bentazon; chlorimuron; glyphosate; imazaquin; imazethapyr; pendimethalin; thifensulfuron; soybean, Glycine max (L.) Merr. ‘Asgrow 4401 RR’. Additional index words: Herbicide injury, soil-applied herbicides, preemergence, postemergence. Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate.

Influence of Plant Height and Glyphosate on Saflufenacil Efficacy on Glyphosate-Resistant Horseweed (Conyza canadensis)

Abstract A field study was conducted in 2007 and 2008 near Murphysboro, IL to determine the effect of plant height and addition of glyphosate on control of glyphosate-resistant horseweed with saflufenacil. Saflufenacil was applied at rates ranging from 25 to 125 g ai ha−1 alone and in combination with glyphosate at 840 g ae ha−1, and the efficacy compared to paraquat at 840 g ai ha−1. Control of horseweed with glyphosate applied alone was less than 30%, confirming the presence of glyphosate-resistant plants. At 14 d after application, all treatments with saflufenacil or paraquat provided at least 90% control. Saflufenacil applied alone at the lowest rate of 25 g ha−1 provided less control (92%) than all other treatments that included saflufenacil, and efficacy was reduced as horseweed height at application increased. Horseweed control from saflufenacil at 50 g ha−1 was reduced as plant height increased in 2007 but not in 2008. However, saflufenacil applied at 50 g ha−1 or greater resulted in at least 98% control, regardless of horseweed height at application or tank mixture with glyphosate. Combining glyphosate with saflufenacil at 25 g ha−1 increased horseweed control compared with saflufenacil applied alone and resulted in control similar to saflufenacil applied at 50 g ha−1. Control of horseweed from paraquat declined over time as the growth continued from the apical meristem. The extent of horseweed regrowth from applications of saflufenacil alone was less than that observed from paraquat. The addition of glyphosate to saflufenacil further reduced the frequency of horseweed regrowth compared with saflufenacil applied alone. Nomenclature: Glyphosate; paraquat; saflufenacil; horseweed; Conyza canadensis (L.) Cronq. Resumen En 2007 y 2008, se realizó un estudio cerca de Murphysboro, IL para determinar el efecto de la altura de planta y la adición de glyphosate sobre el control de Conyza canadensis resistente a glyphosate con saflufenacil. Saflufenacil fue aplicado a dosis que fueron de 25 a 125 g ai ha−1 solo y en combinación con glyphosate a 840 g ae ha−1, y la eficacia de estos tratamientos se comparó con paraquat a 840 g ai ha−1. El control de C. canadensis con glyphosate aplicado solo fue menor a 30%, confirmando la presencia de plantas resistentes a glyphosate. A 14 d después de la aplicación, todos los tratamientos con saflufenacil o paraquat brindaron al menos 90% de control. Saflufenacil aplicado solo a la dosis más baja de 25 g ha−1 brindó menos control (92%) que todos los demás tratamientos que incluyeron saflufenacil, y la eficacia se redujo al incrementarse la altura de la maleza al momento de la aplicación. El control de C. canadensis con saflufenacil a 50 g ha−1 se redujo al aumentar la altura de las plantas al momento de la aplicación en 2007, pero no en 2008. Sin embargo, saflufenacil aplicado a 50 g ha−1 o más resultó en al menos 98% de control, sin importar la altura de C. canadensis al momento de la aplicación o la mezcla en tanque con glyphosate. El combinar glyphosate con saflufenacil a 25 g ha−1 aumentó el control de C. canadensis en comparación con saflufenacil aplicado solo y resultó en un control similar a saflufenacil aplicado a 50 g ha−1. El control de C. canadensis con paraquat disminuyó conforme pasó el tiempo y continuó el crecimiento a partir del meristemo apical. El nivel de rebrote de plantas de C. canadensis después de aplicaciones de solo saflufenacil fue menor que el nivel observado con paraquat. La adición de glyphosate a saflufenacil disminuyó aún más la frecuencia de rebrotes de C. canadensis en comparación con la aplicación de saflufenacil solo.

Characterization of PPO-Inhibitor-Resistant Waterhemp (Amaranthus tuberculatus) Response to Soil-Applied PPO-Inhibiting Herbicides

Abstract Waterhemp resistance to foliar applications of protoporphyrinogen oxidase (PPO)–inhibiting herbicides has become increasingly disconcerting given the widespread distribution of glyphosate resistance. Fortunately, soil-residual PPO-inhibiting herbicides remain efficacious in waterhemp populations resistant to PPO-inhibiting herbicides; however, these herbicides should theoretically select for the resistant biotype as herbicide concentrations diminish in the soil. Accordingly, the objectives of this research were twofold: (1) evaluate the efficacy of three PPO-inhibiting herbicides, foliar- and soil-applied, on PPO-resistant (PPO-R) and PPO-susceptible (PPO-S) waterhemp, and (2) investigate the differential effects of PPO-inhibiting herbicides on an R biotype and an S biotype during several discrete developmental events relevant to soil–residual herbicide activity (i.e., radicle protrusion, radicle elongation, and waterhemp emergence). Greenhouse and growth chamber experiments indicated that the R biotype was least sensitive to the diphenylether herbicide fomesafen, followed by sulfentrazone and flumioxazin; however, fomesafen plus s-metolachlor improved soil-residual efficacy over fomesafen alone. Growth stage considerably influenced the R : S ratio, decreasing from 38× to 3.4×, when comparing ratios generated from foliar applications and soil-residual applications measuring radicle protrusion, respectively. Overall, this research supports the use of full soil-residual herbicide rates, reinforcing the importance of best management practices to manage the spread of herbicide resistance. Nomenclature: Flumioxazin; fomesafen; glyphosate; s-metolachlor; sulfentrazone; tall waterhemp, Amaranthus tuberculatus (Moq.) Sauer (syn. rudis) AMATA.

Agricultural Weeds in Glyphosate-Resistant Cropping Systems in the United States

Abstract A segment of the debate surrounding the commercialization of genetically engineered (GE) crops, such as glyphosate-resistant (GR) crops, focuses on the theory that implementation of these traits is an extension of the intensification of agriculture that will further erode the biodiversity of agricultural landscapes. A large field-scale study was conducted in 2006 in the United States on 156 different field sites with a minimum 3-yr history of GR corn, cotton, or soybean in the cropping system. The impact of cropping system, crop rotation, frequency of using the GR crop trait, and several categorical variables on emerged weed density and diversity was analyzed. Species richness, evenness, Shannons H′, proportion of forbs, erect growth habit, and C3 species diversity were all greater in agricultural sites that lacked crop rotation or were in a continuous GR crop system. Rotating between two GR crops (e.g., corn and soybean) or rotating to a non-GR crop resulted in less weed diversity than a continuous GR crop. The composition of the weed flora was more strongly related to location (geography) than any other parameter. The diversity of weed flora in agricultural sites with a history of GR crop production can be influenced by several factors relating to the specific method in which the GR trait is integrated (cropping system, crop rotation, GR trait rotation), the specific weed species, and the geographical location. The finding that fields with continuous GR crops demonstrated greater weed diversity is contrary to arguments opposing the use of GE crops. These results justify further research to clarify the complexities of crops grown with herbicide-resistance traits, or more broadly, GE crops, to provide a more complete characterization of their culture and local adaptation. Nomenclature: Glyphosate; corn, Zea mays L. ZEAMX; cotton, Gossypium hirsutum L. GOSHI; soybean, Glycine max (l.) Merr. GLXMA.

Seedbank and Field Emergence of Weeds in Glyphosate-Resistant Cropping Systems in the United States

Abstract A segment of the debate surrounding the commercialization and use of glyphosate-resistant (GR) crops focuses on the theory that the implementation of these traits is an extension of the intensification of agriculture that will further erode the biodiversity of agricultural landscapes. A large field-scale study was initiated in 2006 in the United States on 156 different field sites with a minimum 3-yr history of GR-corn, -cotton or -soybean in the cropping system. The impact of cropping system, crop rotation, frequency of using the GR crop trait, and several categorical variables on seedbank weed population density and diversity was analyzed. The parameters of total weed population density of all species in the seedbank, species richness, Shannons H′ and evenness were not affected by any management treatment. The similarity between the seedbank and aboveground weed community was more strongly related to location than management; previous years crops and cropping systems were also important while GR trait rotation was not. The composition of the weed flora was more strongly related to location (geography) than any other parameter. The diversity of weed flora in agricultural sites with a history of GR crop production can be influenced by several factors relating to the specific method in which the GR trait is integrated (cropping system, crop rotation, GR trait rotation), the specific weed species, and the geographical location. Continuous GR crop, compared to fields with other cropping systems, only had greater species diversity (species richness) of some life forms, i.e., biennials, winter annuals, and prostrate weeds. Overall diversity was related to geography and not cropping system. These results justify further research to clarify the complexities of crops grown with herbicide-resistance traits to provide a more complete characterization of their culture and local adaptation to the weed seedbank. Nomenclature: Glyphosate; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

Application Timing Determines Giant Foxtail (Setaria faberi) and Barnyardgrass (Echinochloa crus-galli) Control in No-Till Corn (Zea mays)'

Abstract: Field studies were conducted from 1996 to 1998 to evaluate grass control in no-till corn (Zea mays) with herbicides applied early preplant (EPP), preemergence (PRE), and postemergence (POST) at the Belleville Research Center at Belleville, IL. Grass control was affected by application timing rather than herbicide. The herbicides applied PRE provided more consistent giant foxtail (Setaria faberi) and barnyardgrass (Echinochloa crus-galli) control (90 to 98%) than the same herbicides applied EPP (0 to 92%). There also was no difference in giant foxtail and barnyardgrass control between the emulsifiable concentrate (EC) formulation and microencapsulated (ME) formulation of acetochlor. Rimsulfuron plus thifensulfuron applied POST provided 90 to 97% control of giant foxtail and barnyardgrass. Metolachlor, EC-acetochlor, SAN 582H, and rimsulfuron plus thifensulfuron provided 85 to 92% control of yellow nutsedge (Cyperus esculentus) compared with 63 to 74% control for BAY FOE 5043 plus metribuzin and ME-acetochlor. Corn grain yield was greater with herbicides applied either PRE or POST than applied EPP. Grass control and grain yield were greater with herbicides applied either PRE or POST compared with EPP. Nomenclature: Acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide; BAY FOE 5043 (proposed name, flufenacet), N-(4-fluorophenyl)-N-(1-methylethyl)-2-[[5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl]oxy]acetamide; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one; rimsulfuron, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfonamide; SAN 582H (proposed name, dimethenamid), 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl) acetamide; thifensulfuron, 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] amino]sulfonyl]-2-thiophenecarboxylic acid; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; giant foxtail, Setaria faberi Herrm. # SETFA; yellow nutsedge, Cyperus esculentus L. # CYPES; corn, Zea mays L. ‘Pioneer 3335’. Additional index words: Early preplant, preemergence, postemergence. Abbreviations: DAP, days after planting; EC, emulsifiable concentrate formulation; EPP, early preplant; ME, microencapsulated formulation; POST, postemergence; PRE, preemergence.

Occurrence of an herbicide‐resistant plant trait in agricultural field margins

Abstract Agricultural environments allow study of evolutionary change in plants. An example of evolution within agroecological systems is the selection for resistance to the herbicide glyphosate within the weed, Conyza canadensis. Changes in survivorship and reproduction associated with the development of glyphosate resistance (GR) may impact fitness and influence the frequency of occurrence of the GR trait. We hypothesized that site characteristics and history would affect the occurrence of GR C. canadensis in field margins. We surveyed GR occurrence in field margins and asked whether there were correlations between GR occurrence and location, crop rotation, GR crop trait rotation, crop type, use of tillage, and the diversity of herbicides used. In a field experiment, we hypothesized that there would be no difference in fitness between GR and glyphosate‐susceptible (GS) plants. We asked whether there were differences in survivorship, phenology, reproduction, and herbivory between 2 GR and 2 GS populations of C. canadensis in agrestal and ruderal habitats. We found that geographic location was an important factor in the occurrence of GR C. canadensis in field margins. Although not consistently associated with either glyphosate resistance or glyphosate susceptibility, there were differences in phenology, survivorship, and herbivory among biotypes of C. canadensis. We found equal or greater fitness in GR biotypes, compared to GS biotypes, and GR plants were present in field margins. Field margins or ruderal habitats may provide refugia for GR C. canadensis, allowing reproduction and further selection to occur as seeds recolonize the agrestal habitat. Agricultural practices may select for ecological changes that feed back into the evolution of plants in ruderal habitats.