Zahoor A. Ganie

Integrated Management of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida) with Tillage and Herbicides in Soybean

Giant ragweed is one of the most competitive annual broadleaf weeds in soybean production fields in the midwestern United States and eastern Canada because of its early emergence, rapid growth rate, high plasticity, and resistance to glyphosate and acetolactate synthase inhibitors. Therefore, early-season management of giant ragweed is critical to avoid yield loss. The objectives of this study were to evaluate control of glyphosate-resistant giant ragweed through the integration of preplant tillage or 2,4-D; PRE or early POST (EPOST) followed by (fb) late POST (LPOST) herbicide programs with or without preplant tillage or 2,4-D; and their effect on soybean injury and yield. A field study was conducted in 2013 and 2014 in David City, NE in a field infested with glyphosate-resistant giant ragweed. Preplant tillage or 2,4-D application provided > 90% control of glyphosate-resistant giant ragweed 14 d after preplant treatment. Giant ragweed control and biomass reduction were consistently > 90% with preplant tillage or 2,4-D fb sulfentrazone plus cloransulam PRE or glyphosate plus cloransulam EPOST fb glyphosate plus fomesafen or lactofen LPOST compared with ≤ 86% control with same treatments without preplant tillage or 2,4-D. PRE or EPOST fb LPOST herbicide programs preceded by preplant treatments resulted in giant ragweed density < 2 plants m−2 and soybean yield > 2,400 kg ha−1 compared with the density of ≥ 2 plants m−2 and soybean yield < 1,800 kg ha−1 under PRE or EPOST fb LPOST herbicide programs. The contrast analysis also indicated that preplant tillage or 2,4-D fb a PRE or POST program was more effective for giant ragweed management compared with PRE fb POST herbicide programs. Integration of preplant tillage would provide an alternative method for early-season control of giant ragweed; however, a follow up application of herbicides is needed for season-long control in soybean. Nomenclature: 2,4-D amine; cloransulam; fomesafen; lactofen; sulfentrazone; giant ragweed, Ambrosia trifida L.; soybean, Glycine max (L.) Merr. Ambrosia trifida es una de las malezas de hoja ancha más competitivas en campos de producción de soja en el centro-oeste de los Estados Unidos y en el este de Canada debido a su emergencia temprana, alta tasa crecimiento, alta plasticidad, y resistencia a glyphosate e inhibidores de acetolactate synthase. Por esta razón, el manejo de A. trifida, temprano durante la temporada de crecimiento, es crítico para evitar las pérdidas de rendimiento. Los objetivos de este estudio fueron evaluar el control de A. trifida resistente a glyphosate mediante la integración de labranza en pre-siembra o 2,4-D; aplicaciones PRE o POST temprana (EPOST) seguido por (fb) programas de herbicidas en POST tardía (LPOST) con o sin labranza en pre-siembra o 2,4-D; y su efecto sobre el daño y rendimiento de la soja. Se realizó un estudio de campo en 2013 y 2014 en David City, Nebraska en un campo infestado con A. trifida resistente a glyphosate. La labranza en pre-siembra o la aplicación de 2,4-D brindó >90% de control de A. trifida resistente a glyphosate 14 d después del tratamiento pre-siembra. El control y la reducción en la biomasa de A. trifida fueron >90% consistentemente con la labranza pre-siembra o 2,4-D fb sulfentrazone más cloransulam PRE o glyphosate más cloransulam EPOST fb glyphosate más fomesafen o lactofen POST al compararlo con ≤86% de control con los mismos tratamientos sin labranza pre-siembra o 2,4-D. Programas de herbicidas PRE o de EPOST fb LPOST precedidos por tratamientos pre-siembra resultaron en una densidad de A. trifida <2 plantas m−2 y un rendimiento de soja >2,400 kg ha−1 al compararse con la densidad de ≥2 plantas m−2 y un rendimiento de soja ≤1,800 kg ha−1 con programas de herbicidas PRE o EPOST fb LPOST. El análisis de contrastes también indicó que la labranza pre-siembra o 2,4-D fb de un programa PRE o POST fue más efectiva para el manejo de A. trifida al compararse con programas de herbicidas PRE fb POST. La integración de labranza pre-siembra brindaría una alternativa de manejo para el control de A. trifida, temprano en la temporada. Sin embargo, se requiere que a esto le siga una aplicación de herbicidas para obtener un control a lo largo de toda la temporada en soja.

Integrated Weed Management in Maize

The corn plant is one of nature’s most amazing energy-storing devices. Weed management is one of the important practices for successful corn production. Herbicide-resistant corn hybrids (including glyphosate-, glufosinate-, and imidazolinone-resistant) have been adopted by corn producers primarily in the Americas. Glyphosate-resistant corn is the most widely grown herbicide-resistant variety by corn producers. This technology has provided excellent weed control for a decade; however, continuous and multiple applications of glyphosate in the corn–soybean cropping system have resulted in weed shifts and evolved glyphosate-resistant weed biotypes. This is the best example of negative implication of relying on a single method of weed control for many years. A well-planned weed management program in corn should involve multiple strategies, including preventive techniques, such as monitoring, cultural control, mechanical or physical control, and chemical control tactics. Preventive techniques may start with planting weed-free crop seeds or choosing an alternative field. Rotating crops to disrupt pest life cycles and planting adapted varieties are good examples of cultural control. Mechanical or physical control may include tillage and mowing to disrupt certain hard-to-control and perennial weeds. Flaming for weed control has been receiving attention of several corn producers in North Central USA and Europe, and it can be an important tool in an integrated weed management program. Use of herbicides is still the primary, efficient, and the most economical way for weed control in corn, but their use should be based on a sound management decision and rotation. Several existing corn herbicides have been tank-mixed or sold as premixed. They have been used extensively for control of herbicide-resistant weeds. Multiple herbicide-resistant corn (glyphosate plus 2,4-dichlorophenoxyacetic acid resistant; glyphosate plus glufosinate plus 2,4-D resistant) has been developed by industry and currently pending regulatory approval. Upon commercialization (once all regulatory approvals are secured), they may be effective for control of herbicide-resistant weeds; however, continuous use of the same trait and herbicides may promote evolution of multiple herbicide-resistant weeds.

Glyphosate-Resistant Common Ragweed (Ambrosia artemisiifolia) in Nebraska: Confirmation and Response to Postemergence Corn and Soybean Herbicides

Common ragweed is an important broadleaf weed in agronomic crops in the northcentral United States. A common ragweed biotype in glyphosate-resistant (GR) soybean production field in southeast Nebraska was not controlled after sequential applications of glyphosate at the labeled rate. The objectives of this study were to confirm GR common ragweed in Nebraska by quantifying the level of resistance in greenhouse and field whole-plant dose-response studies and to evaluate the response of the putative GR common ragweed to POST corn and soybean herbicides. Greenhouse wholeplant dose-response studies confirmed 7- and 19-fold resistance to glyphosate compared to the known glyphosate-susceptible (GS) biotype based on biomass reduction and control estimates, respectively. Field dose-response studies conducted in 2015 and 2016 at the putative GR common ragweed research site suggested that glyphosate doses equivalent to 15- and 40-times the labeled rate (1,260 g ae ha-1) were required for 90% control and biomass reduction, respectively. Response of GR common ragweed to POST soybean herbicides in greenhouse studies indicated ≥89% control with acifluorfen, fomesafen, fomesafen plus glyphosate, glyphosate plus dicamba or 2,4-D choline, glufosinate, imazamox plus acifluorfen, and lactofen. POST corn herbicides, including 2,4-D, bromoxynil, diflufenzopyr plus dicamba, glufosinate, halosulfuron-methyl plus dicamba, mesotrione plus atrazine, and tembotrione provided ≥87% control, indicating that POST herbicides with distinct modes of action are available in corn and soybean for effective control of GR common ragweed. Results also suggested a reduced efficacy of the acetolactate synthase (ALS)-inhibiting herbicides tested in this study for control of GR and GS biotypes, indicating further research is needed to determine whether this biotype has evolved multiple herbicide resistance. Nomenclature: 2,4-D; acifluorfen; atrazine; bentazon; bromoxynil; carfentrazone; chlorimuron; dicamba; fluthiacet; fomesafen; glufosinate; glyphosate; halosulfuron; imazethapyr; imazamox lactofen; mesotrione; primisulfuron; tembotrione; thifensulfuron; topramezone; common ragweed, Ambrosia artemisiifolia L.; corn, Zea mays L.; soybean, Glycine max (L.) Merr

Temperature Influences Efficacy, Absorption, and Translocation of 2,4-D or Glyphosate in Glyphosate-Resistant and Glyphosate-Susceptible Common Ragweed (Ambrosia artemisiifolia) and Giant Ragweed (Ambrosia trifida)

Glyphosate and 2,4-D have been commonly used for control of common and giant ragweed before planting of corn and soybean in the midwestern United States. Because these herbicides are primarily applied in early spring, environmental factors such as temperature may influence their efficacy. The objectives of this study were to (1) evaluate the influence of temperature on the efficacy of 2,4-D or glyphosate for common and giant ragweed control and the level of glyphosate resistance and (2) determine the underlying physiological mechanisms (absorption and translocation). Glyphosate-susceptible (GS) and glyphosate-resistant (GR) common and giant ragweed biotypes from Nebraska were used for glyphosate dose–response studies, and GR biotypes were used for 2,4-D dose–response studies conducted at two temperatures (day/night [d/n]; low temperature [LT]: 20/11 C d/n; high temperature [HT]: 29/17 C d/n). Results indicate improved efficacy of 2,4-D or glyphosate at HT compared with LT for common and giant ragweed control regardless of susceptibility or resistance to glyphosate. The level of glyphosate resistance decreased in both the species at HT compared with LT, primarily due to more translocation at HT. More translocation of 2,4-D in GR common and giant ragweed at HT compared with LT at 96 h after treatment could be the reason for improved efficacy. Similarly, higher translocation in common ragweed and increased absorption and translocation in giant ragweed resulted in greater efficacy of glyphosate at HT compared with LT. It is concluded that the efficacy of 2,4-D or glyphosate for common and giant ragweed control can be improved if applied at warm temperatures (29/17 C d/n) due to increased absorption and/or translocation compared with applications during cooler temperatures (20/11 C d/n). Nomenclature: 2,4-D, glyphosate; common ragweed, Ambrosia artemisiifolia L.; giant ragweed, Ambrosia trifida L.; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Response of selected glyphosate-resistant broadleaved weeds to premix of fluthiacet-methyl and mesotrione (Solstice TM ) applied at two growth stages

Ganie, Z. A., Stratman, G. and Jhala, A. J. 2015. Response of selected glyphosate-resistant broadleaved weeds to premix of fluthiacet-methyl and mesotrione (Solstice™) applied at two growth stages. Can. J. Plant Sci. 95: 861-869. A premix of fluthiacet-methyl and mesotrione (1:17.5 ratio) has recently been registered for post-emergence (POST) broadleaf weed control in corn. The objective of this study was to determine the response of glyphosate-resistant common waterhemp, giant ragweed, and kochia to a premix of fluthiacet-methyl and mesotrione when applied to 10- and 20-cm-tall plants. Greenhouse dose response studies were conducted and log-logistic models were used to determine how the response varies between the weed species at two growth stages under various rates ranging from 21.8 to 218.5 g a.i. ha-1 (0.25× to 2.5×). The effective rate required to achieve >90% control and shoot biomass reduction varied depending on the weed species and growth stage. The rates required for 90% control (ED90) of 10-cm-tall glyphosate-resistant common waterhemp, giant ragweed, and kochia were 78, 251, and 17 g a.i. ha-1, respectively, compared with 144, 489, and 79,349 g a.i. ha-1, respectively, for 20-cm-tall plants at 21 d after treatment (DAT). Based on visual control estimates at ED90 level, glyphosate-resistant common waterhemp was the most sensitive at both growth stages; kochia was sensitive at 10-cm height, while giant ragweed was the least sensitive at both growth stages. Irrespective of weed species or growth stage, the ED90 values calculated on the basis of shoot biomass reduction were mostly higher compared with visual control estimates. It is concluded that premix of fluthiacet-methyl plus mesotrione can be potentially used as a POST herbicide in corn for controlling glyphosate-resistant common waterhemp and kochia (≤ 10 cm tall) at the labeled rate (87 g a.i. ha-1).

Interaction of 2,4-D or Dicamba with Glufosinate for Control of Glyphosate-Resistant Giant Ragweed ( Ambrosia trifida L.) in Glufosinate-Resistant Maize ( Zea mays L.)

Glyphosate-resistant (GR) giant ragweed is a problematic broadleaf weed in crops including maize and soybean in the Midwestern United States. Commercialization of crops with 2,4-D or dicamba and glufosinate resistance will allow post-emergence (POST) applications of these herbicides. Therefore, information is needed on how 2,4-D/dicamba will interact with glufosinate in various rate combinations. The objectives of this study were to evaluate the interaction of glufosinate plus 2,4-D and/or dicamba for control of GR giant ragweed, and to determine their effect on GR giant ragweed density, biomass, maize injury, and yield. Field experiments were conducted in 2013 and 2014 in a field infested with GR giant ragweed in Nebraska, United States. The treatments included POST applications of glufosinate (450 or 590 g ai ha-1), 2,4-D, or dicamba at 280 or 560 g ae ha-1 applied alone and in tank-mixtures in glufosinate-resistant maize. The results showed that dicamba applied alone resulted in 56 to 62% and 73 to 83% control at 14 and 28 days after treatment (DAT), respectively, and ≥95% control at 60 DAT or at harvest compared to 17 to 30% and 57 to 73% control with 2,4-D applied alone at 280 and 560 g ai ha-1, respectively. Glufosinate tank-mixed with 2,4-D and/or dicamba consistently provided ≥89% control of GR giant ragweed, except that control with glufosinate plus 2,4-D varied from 80 to 92% at 60 DAT and at harvest. The comparison between the observed and expected control (determined by Colby’s equation) suggested an additive interaction between glufosinate and 2,4-D or dicamba for control of GR giant ragweed. Contrast analysis also indicated that GR giant ragweed control with glufosinate plus 2,4-D or dicamba was either consistently higher or comparable with individual herbicides excluding 2,4-D applied alone. Herbicide programs, excluding 2,4-D at 280 g ae ha-1, resulted in ≥80% reduction in GR giant ragweed density. Tank-mixing glufosinate with 2,4-D or dicamba showed an additive effect and will be an additional tool with two effective modes of action for the management of GR giant ragweed in maize.

Modeling pollen-mediated gene flow from glyphosate-resistant to -susceptible giant ragweed (Ambrosia trifida L.) under field conditions

A field experiment was conducted to quantify pollen mediated gene flow (PMGF) from glyphosate-resistant (GR) to glyphosate-susceptible (GS) giant ragweed under simulated field conditions using glyphosate resistance as a selective marker. Field experiments were conducted in a concentric design with the GR giant ragweed pollen source planted in the center and GS giant ragweed pollen receptors surrounding the center in eight directional blocks at specified distances (between 0.1 and 35 m in cardinal and ordinal directions; and additional 50 m for ordinal directions). Seeds of GS giant ragweed were harvested from the pollen receptor blocks and a total of 100,938 giant ragweed plants were screened with glyphosate applied at 2,520 g ae ha−1 and 16,813 plants confirmed resistant. The frequency of PMGF was fit to a double exponential decay model selected by information-theoretic criteria. The highest frequency of gene flow (0.43 to 0.60) was observed at ≤0.5 m from the pollen source and reduced rapidly with increasing distances; however, gene flow (0.03 to 0.04) was detected up to 50 m. The correlation between PMGF and wind parameters was inconsistent in magnitude, direction, and years.

Overlapping Residual Herbicides for Control of Photosystem (PS) II- and 4-Hydroxyphenylpyruvate Dioxygenase (HPPD)-Inhibitor-Resistant Palmer amaranth ( Amaranthus palmeri S. Watson) in Glyphosate-Resistant Maize

A Palmer amaranth (Amaranthus palmeri S. Watson) biotype has evolved resistance to photosystem (PS) II- (atrazine) and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides (mesotrione, tembotrione, and topramezone) in maize seed production field in Nebraska, USA. The objectives of this study were to determine the effect of soil residual pre-emergence (PRE) herbicides followed by (fb) tank-mixture of residual and foliar active post-emergence (POST) herbicides on PS-II- and HPPD-inhibitor-resistant Palmer amaranth control, maize yield, and net economic returns. Field experiments were conducted in a growers field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska, USA in 2015 and 2016. The contrast analysis suggested that saflufenacil plus dimethenamid-P or pyroxasulfone plus saflufenacil applied PRE provided 80–82% Palmer amaranth control compared to 65 and 39% control with saflufenacil and pyroxasulfone applied alone at 3 weeks after PRE (WAPRE), respectively. Among the PRE fb POST herbicide programs, 95–98% Palmer amaranth control was achieved with pyroxasulfone plus safluefenacil, or saflufenacil plus dimethenamid-P applied PRE, fb glyphosate plus topramezone plus dimethenamid-P plus atrazine, glyphosate plus diflufenzopyr plus dicamba plus pyroxasulfone, glyphosate plus diflufenzopyr plus pendimethalin, or glyphosate plus diflufenzopyr plus dicamba plus atrazine applied POST at 3 weeks after POST (WAPOST) through maize harvest. Based on contrast analysis, PRE fb POST programs provided 77–83% Palmer amaranth control at 3 WAPOST through maize harvest compared to 12–15% control with PRE-only and 66–84% control with POST-only programs. Similarly, PRE fb POST programs provided 99% biomass reduction at 6 WAPOST compared to PRE-only (28%) and POST-only (87%) programs. PRE fb POST programs provided higher maize yield (13,617 kg ha−1) and net return (US

Rice Production in the Americas

1,724 ha−1) compared to the PRE-only (2,656 kg ha−1; US

Effect of Late-Season Herbicide Applications on Inflorescence and Seed Production of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida)

285 ha−1) and POST-only (11,429 kg ha−1; US