A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in ... more A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in media containing the herbicide atrazine at concentrations up to 100-fold greater than the lethal concentration (1.0 {mu}M) for the unselected (wild type) cell line. The basis for atrazine resistance could not be identified by differential uptake or metabolism. Photosynthetic electron transport rates for both intact cell and isolated thylakoid membranes from chloroplasts were unaffected in variant cells at atrazine concentrations up to 100-fold greater than for wild type cells. Photoaffinity labeling of isolated thylakoid membranes from both cell lines with {sup 14}C-azidoatrazine revealed an altered Q{sub B} polypeptide in variant cells resulting in low or no affinity for atrazine. A portion of the chloroplast psbA gene, encoding the Q{sub B} polypeptide, was sequenced for both cell lines. The basis for atrazine resistance in variant cells was identified as a single base change resulting in the alteration of serine to threonine at position 264 of the Q{sub B} polypeptide. In addition to atrazine resistance, variant cells exhibit enhanced tolerance to the herbicides DCMU and metribuzin, but greater sensitivity to bentazon. No reductions in variant cell growth and photosynthetic efficiency in the absence of atrazine were observed.
A mutation of the psbA gene was identified in photoautotrophic potato (Solanum tuberosum 1. cv Su... more A mutation of the psbA gene was identified in photoautotrophic potato (Solanum tuberosum 1. cv Superior x U.S. Department of Agriculture line 66-142) cells selected for resistance to 6-chloro-N-ethyl-N'-(l-methylethyl)-l,3,5-triazine-2,4-diamine (atrazine). Photoaffinity labeling with 6-azido-N-ethyl-N'-(l-methyIethyl)-1,3,5-triazine-2,4-diamine detected a thylakoid membrane protein with a M. of 32,000 in susceptible, but not in resistant, cells. This protein was identified as the secondary quinone acceptor of photosystem II (QB) protein. Atrazine resistance in selected cells was attributable to a mutation from ACT (serine) to ACT (threonine) in codon 264 of the psbA gene that encodes the Q. protein. Although the mutant cells exhibited extreme levels of resistance to atrazine, no concomitant reductions in photosynthetic electron transport or cell growth rates compared to the unselected cells were detected. This is in contrast with the losses in productivity observed in atrazine-resistant mutants that contain a glycine-264 alteration. Prolonged agronomic use of PSII inhibitors, specifically striazine herbicides, has resulted in the evolution of resistant weed biotypes. The predominant basis for resistance is a single nucleotide substitution in the chloroplast psbA gene (Mazur and Falco, 1989), which encodes the D1 thylakoid protein (termed the Q B protein) and is the target molecule for s-triazine binding. In a11 resistant weed biotypes examined to date, the specific mutation is a G for A substitution that results in a change from Ser to Gly in position 264 of the mature QB protein (Blyden and Gray, 1986; Bettini et al., 1987; Barros and Dyer, 1988; Mazur and Falco, 1989). This mutation effectively eliminates s-triazine binding affinity to the protein. s-Triazine resistance has been stably transferred from weed to crop species by both interspecific (Ayotte et al., 1987) and somatic cell hybridization (Binding et al., 1982). Transgenic plants that express a nuclear gene encoding a modified Q B protein with a single peptide for chloroplast targeting of the protein also exhibited increased atrazine tolerance (Cheung et al., 1988). Incorporation of s-triazine resistance into crops Joumal paper No.
Juniper online journal of public health, Aug 15, 2023
Although dicamba can move long distances via off-target movement [5], significant damage to tomat... more Although dicamba can move long distances via off-target movement [5], significant damage to tomato, potato and watermelon has also been recorded at representative drift rates. [4] found that watermelon treated 20 days after planting (DAP) with 7.5 g ae ha-1 of the label rate of dicamba exhibited 40% visual injury and had vine lengths 49% the length of the non-treated
Journal of Agricultural and Food Chemistry, Mar 12, 2010
Greenhouse and laboratory experiments were conducted to investigate differences in glyphosate sus... more Greenhouse and laboratory experiments were conducted to investigate differences in glyphosate susceptibility among three species of the genus Conyza introduced as weeds in Spain: tall fleabane (Conyza sumatrensis), hairy fleabane (Conyza bonariensis), and horseweed (Conyza canadensis). Plant material was obtained from seeds collected in weed populations growing in olive groves and citrus orchards in southern Spain, with no previous history of glyphosate application. Dose-response curves displayed ED(50) values of 2.9, 15.7, and 34.9 g ai ha(-1), respectively, for C. sumatrensis, C. bonariensis, and C. canadensis plants at the rosette stage (6-8 leaves). Significant differences were found among the three species in the glyphosate retention on leaves as well as the leaf contact angle. The species order according to glyphosate retention was C. sumatrensis > C. bonariensis > C. canadensis, while the mean contact angles of glyphosate droplets were 59.2, 65.5, and 72.9 degrees , respectively. There were no significant differences among species in the absorption of [(14)C]glyphosate (ranged from 37.4% for C. canadensis to 52.4% for C. sumatrensis), but the order among species was the same as glyphosate retention. The amount of radioactivity translocated from treated leaves was lower in C. canadensis as compared to the other two species (C. sumatrensis > C. bonariensis > C. canadensis). Combined, all of the studied parameters identified differential susceptibility to glyphosate among the Conyza species. Each species accumulated shikimate in leaf tissues following application of glyphosate at 200 g ai ha(-1). However, C. canadensis exhibited lower shikimate levels than the other two species at 168 h after herbicide application. For hairy fleabane, a greenhouse study explored its susceptibility to glyphosate at three developmental stages: rosette, bolting (stem height, 10-15 cm), and flowering. The ED(50) was lower at the rosette stage (15.7 g ai ha(-1)) as compared to bolting (86.6 g ai ha(-1)), with the highest ED(50) values occurring at flowering (117.5 g ai ha(-1)); plants at the earlier developmental stage retained more glyphosate. These results agree with field observations that plants at early developmental stages are more sensitive to glyphosate.
A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in ... more A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in media containing in the herbicide atrazine at concentration up to 100 x greater than the lethal concentration for the unselected (wild type) cell line (1.0 {mu}M). Fresh weight doubling times of variant cells in the presence or absence of 1.0 {mu}M atrazine were identical to wild type cells grown in the absence of atrazine. Maintenance of variant cells up to 10 passages in the absence of atrazine resulted in a reduction in the concentration of atrazine necessary to inhibit fresh weight gain by 99% (ID{sub 99}) from 100 to 80 {mu}M. Comparison of {sup 14}C-atrazine uptake indicated wild type cells accumulated up to 2.5-fold more atrazine than varient cells within 72h of exposure but no differences were detected thereafter. Electron transport of both isolated chloroplasts and intact cells were significantly inhibited in the wild type cell line by 1.0 {mu}M atrazine but unaffected in the variant cell line by atrazine concentrations up to 10 {mu}M. After 30 days in the presence of 1.0 {mu}M atrazine, wild type cells did not significantly metabolize atrazine, however, variant cells reduced atrazine concentrations to <0.05 {mu}M regardless if themore » initial atrazine concentration was 1.0 or 10.0 {mu}M. Both metabolism of atrazine and alterations within the chloroplast (potentially a reduction in atrazine binding affinity) appear to be important components of tolerance within variant cells.« less
Windmillgrass (Chloris verticillata Nutt.) is spreading from native areas, becoming problematic i... more Windmillgrass (Chloris verticillata Nutt.) is spreading from native areas, becoming problematic in established turf in Missouri, and surrounding states. Limited information is available regarding post-emergence (POST) control options for turf. The objective of this research was to assess the visual and biomass response of windmillgrass to selected herbicides approved for use in turf. In one study, a greenhouse experiment was conducted with POST application of seven selected herbicides, including dimethylamine salt of quinclorac, fenoxaprop-P-ethyl, foramsulfuron, mesotrione, sulfentrazone, and topramezone in a tank-mixture with triclopyr, as well as a pre-packed product containing thiencarbazone-methyl, foramsulfuron, and halosulfuron-methyl. Under the same experimental conditions, five additional treatments, including mesotrione or topramezone applied at label-suggested rates alone or in combination with triclopyr, in addition to triclopyr alone, were applied to a second study on tillering windmillgrass. At 4 weeks after treatment (WAT), only fenoxaprop-p-ethyl consistently resulted in a complete control of windmillgrass. No measurable regrowth of plants was observed two weeks following the initial collection of windmillgrass aboveground biomass. In the second study, combinations of mesotrione and topramezone with triclopyr resulted in 100% visual injury of windmillgrass at 4 WAT; mesotrione and topramezone alone only resulted in up to 66% visual injury. Triclopyr alone resulted in 91% injury at 4 WAT. The greatest reduction of windmillgrass biomass and least amount of regrowth resulted from mesotrione and topramezone combinations with triclopyr. Control of windmillgrass is effective with fenoxaprop-P-ethyl alone, but use of a 4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor such as mesotrione and topramezone should include the addition of triclopyr.
weed in the pigweed family that is found throughout the Midwest. Waterhemp seedlings have oar-sha... more weed in the pigweed family that is found throughout the Midwest. Waterhemp seedlings have oar-shaped or oval cotyledons (seed leaves) and are hairless (Figure 1), unlike redroot or smooth pigweed. Mature waterhemp plants have long, lance-shaped leaves that are waxy or glossy in appearance (Figure 2). Plants can range in height from 4 inches to 12 feet depending on growing conditions, and they can grow as much as 1 inch per day during the summer growing season. In surveys conducted in Illinois and Missouri, producers and agricultural retailers listed waterhemp as one of the most common and troublesome weeds encountered in soybean production. Waterhemp is a prolific seed producer, capable of producing about one-and-a-half times more seed than most other pigweed species. Waterhemp plants generally produce about 250,000 seeds per plant, although some plants can produce as many as 1 million seeds when growing under optimal conditions in noncompetitive environments. Waterhemp seeds have a discontinuous emergence pattern and can germinate later in the season than most summer annual weed species. This allows waterhemp to escape many preemergence (PRE) herbicide applications and often allows this weed to flourish after postemergence (POST) applications of nonresidual herbicides like glyphosate (sold as Roundup or a variety of other trade names). Waterhemp seed can also persist in the soil for as many as four years with 95 percent of the seed remaining viable after this time.
Palmer amaranth (Amaranthus palmeriS. Watson) is a problematic weed encountered in U.S. cotton (G... more Palmer amaranth (Amaranthus palmeriS. Watson) is a problematic weed encountered in U.S. cotton (Gossypium hirsutumL.) and soybean [Glycine max(L.) Merr.] production, with infestations spreading northward. This research investigated the influence of planting date (early, mid-, and late season) and population (AR, IN, MO, MS, NE, and TN) onA. palmerigrowth and reproduction at two locations. All populations planted early or midseason at Throckmorton Purdue Agricultural Center (TPAC) and Arkansas Agriculture Research and Extension Center (AAREC) measured 196 and 141 cm or more, respectively. Amaranthus palmeriheight did not exceed 168 and 134 cm when planted late season at TPAC and AAREC, respectively. Early season plantedA. palmerifrom NE grew to 50% of maximum height 8 to 13 d earlier than all other populations under TPAC conditions. In addition, the NE population planted early, mid-, and late season achieved 50% inflorescence emergence 5, 4, and 6 d earlier than all other populations, respectively. All populations established at TPAC produced fewer than 100,000 seeds plant−1. No population planted at TPAC and AAREC produced more than 740 and 1,520 g plant−1of biomass at 17 and 19 wk after planting, respectively. Planting date influenced the distribution of male and female plants at TPAC, but not at AAREC. Amaranthus palmerifrom IN and MS planted late season had male-to-female plant ratios of 1.3:1 and 1.7:1, respectively. Amaranthus palmeriintroduced to TPAC from NE can produce up to 7,500 seeds plant−1if emergence occurs in mid-July. An NEA. palmeripopulation exhibited biological characteristics allowing it to be highly competitive if introduced to TPAC due to a similar latitudinal range, but was least competitive when introduced to AAREC. AlthoughA. palmerioriginating from different locations can vary biologically, plants exhibited environmental plasticity and could complete their life cycle and contribute to spreading populations.
Variability in glyphosate efficacy has been observed following late day field applications, but t... more Variability in glyphosate efficacy has been observed following late day field applications, but the influence of this “time-of-day effect” on weed control and soybean yield is unknown. Additionally, the basis for differences in weed control due to application time of day has not been fully elucidated. In field trials, broadleaf weed biomass was ≥5-fold greater when glyphosate was applied at 6:00 A.M. compared to 6:00 P.M. in three of four site–years. No consistent time-of-day effect was observed on treated grass weeds. Soybean yield was unaffected by treatments, and was similar to the weed-free control. In a greenhouse study, both barnyardgrass and velvetleaf biomass were as much as 25 to 80% greater when glyphosate was applied at 8:00 P.M. vs. 2:00 P.M. Examination of individual components of the time-of-day effect for velvetleaf indicated that leaf angle and time of application accounted for 82 and 18%, respectively, of the biomass change. This research suggests that diurnal changes in leaf movement of velvetleaf account for much of the time-of-day effect, with the remainder likely due to an unknown physiological component.
Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and w... more Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and weed control with glufosinate alone or combined with quizalofop, lactofen, imazethapyr, flumiclorac, or bentazon plus acifluorfen in narrow-row, glufosinate-resistant soybean. Soybean injury ranged from 0 to 21% at 2 wk after treatment (WAT) and from 0 to 5% by 4 WAT. Glufosinate alone at 0.29 and 0.4 kg ai/ha controlled velvetleaf, common waterhemp, common ragweed, morningglory species, and giant foxtail greater than 85% in all studies. Mixtures containing glufosinate and other herbicides controlled these species greater than 81% but did not improve control over glufosinate alone. Estimates of weed biomass closely reflected visual control evaluations. However, giant foxtail biomass was higher for mixtures of glufosinate plus lactofen, flumiclorac, or bentazon and acifluorfen, indicating possible antagonism of glufosinate activity. At both locations, soybean yields were similar among most treatments, but that of the glufosinate plus lactofen treatment was lower when compared with other treatments. Additional trials evaluated soybean response and weed control with a preemergence herbicide followed by glufosinate postemergence (POST), glufosinate applied once or twice POST, and mixtures of glufosinate plus imazethapyr or flumiclorac POST in wide-row soybean. Glufosinate applied twice controlled common waterhemp, morningglory species, prickly sida, common cocklebur, and giant foxtail up to 39% greater than did glufosinate applied once. The addition of imazethapyr, but not flumiclorac, to glufosinate improved weed control when compared with glufosinate alone.
Journal of Agricultural and Food Chemistry, Oct 1, 1995
Interaction between a herbicide and plant residue on the soil surface in plant residue management... more Interaction between a herbicide and plant residue on the soil surface in plant residue management systems such as no-tillage or cover crop is of interest in terms of environmental fate of the herbicide. This study was designed to evaluate sorption and desorption of chlorimuron ethyl {ethyl 2-[[[[(4chloro-6-methoxy-2-pyrimidinyl)aminolc~bonyll~olsulfonyllbenzoic acid} in herbicide-desiccated rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) residues and soils collected from a field. Sorption was determined by reacting 0.5 g of soil or plant residue with 6 mL of [14Clchlorimuron ethyl solution at five concentrations (0.06-12.04 pmol L-l) for 72 h. Freundlich Kf was highest in hairy vetch (6.33) followed by rye (3.95) and soils from no cover crop or beneath plant residue (0.81-1.03). The N values (0.88-0.95) for soils and plant residues indicated nearly linear sorption. Time course sorption data analyzed by an equilibriumnetic model indicated that sorption was initially rapid (within 1 h), followed by a negligible increase in soil or a slow increase in rye and hairy vetch residue. Chlorimuron ethyl Kf increased with increased decomposition of plant residue. The Kf for rye and hairy vetch residues sampled at 11 weeks after soybean planting increased by 54 and 49%, respectively, compared with residues sampled at planting. CaCl2-desorbable chlorimuron ethyl in two consecutive 24-h cycles ranged from 54 to 65% in soils and from 42 to 49% of that sorbed in plant residues. Two additional 24-h cycles with methanol/(NH&C03 did not completely desorb the remaining chlorimuron ethyl. Under field conditions, plant residues can apparently intercept and temporarily retain chlorimuron ethyl.
Undesirable stands of hybrid corn often result in a decision to replant; removal of the initial c... more Undesirable stands of hybrid corn often result in a decision to replant; removal of the initial corn is recommended to reduce competition for available resources. Because much of the hybrid corn is glyphosate-resistant (GR), the particular herbicide and timing for control is challenging. No-till field trials were established in central and northeast Missouri in 2009 and 2010 to determine the efficacy of glufosinate POST in glufosinate-resistant corn or imazethapyr plus imazapyr POST in imidazolinone-resistant corn for the control of GR corn. Separate blocks of glufosinate-resistant and imidazolinone-resistant corn were planted in 76 cm rows, with GR corn established between rows at densities of 1 (low) and 4 (high) plants m−2. Herbicides were broadcast at corn heights of 10, 20, and 40 cm. Visual estimates of control rated 5 wk after treatment were highest for the 20 cm application height, ranging from 81 to 84% and 72 to 79% with glufosinate or imazethapyr plus imazapyr, respectively. Control was unacceptable at 10 and 40 cm, ranging from 26 to 62% and 24 to 83%. Dry weights per plant indicated that applications at all heights reduced GR corn biomass a minimum of 94 and 82% with glufosinate or imazethapyr plus imazapyr, respectively. Although control of GR corn with single applications of glufosinate and imazethapyr plus imazapyr was unacceptable for two of three application heights, reductions in corn biomass indicate applications were effective.
Over the past 30 years, numerous reports on herbicide resistance have been published. Although re... more Over the past 30 years, numerous reports on herbicide resistance have been published. Although research in this area is still in its infancy compared to the research done on insecticide and fungicide resistance, there are now more than 80 different plant species worldwide that have developed resistance to one or more herbicides. Mechanisms of herbicide resistance include metabolic detoxification, structural changes in the herbicide’s target site, alterations in the uptake, translocation, or compartmentalization of a herbicide. Although all of these modifications resulting in herbicide resistance in plants have been documented, alteration in the target site is the most common one and provides the highest level of resistance. Resistance has been shown to occur against all major herbicide classes. This chapter will review resistance to all major groups of herbicides, based on mode of action. The appearance of resistance is most likely in monoculture situations in which a herbicide or herbicides with the same mode of action are used continuously. One alarming trend is the emergence of weed species with resistance to herbicides with more than one site of action. This can occur as a result of either some mechanism of metabolic detoxification which degrades many herbicides or alterations in different herbicide target sites, or some combination of both of these mechanisms. Since the world has become very much dependent on herbicides for keeping weeds under control, additional reports on herbicide resistance are urgently needed.
Field experiments were initiated to determine the efficacy of fluazifop as influenced by growth s... more Field experiments were initiated to determine the efficacy of fluazifop as influenced by growth stage for green, yellow, and giant foxtail, large crabgrass, and Japanese millet. Additionally, the influence of air temperature and simulated rainfall on fluazifop efficacy for green foxtail and Japanese millet was determined by greenhouse and growth-room experiments. In both 1983 and 1984, fluazifop activity was reduced as the growth stage increased from 3- to 5- to 7-leaf for all species. Significant differences among species in susceptibility to fluazifop were evident with the descending order of tolerance: green foxtail &gt; large crabgrass &gt; yellow foxtail &gt; giant foxtail &gt; Japanese millet. Increasing the air temperature from 18 to 30 C reduced fluazifop control of green foxtail at herbicide rates less than 0.14 kg ai/ha but did not affect Japanese millet. A 1- to 2-h rain-free interval was required for optimum control of green foxtail and Japanese millet at 0.07 kg/ha fluazifop; the interval was reduced to 45 and 15 min, respectively, when fluazifop rates were 0.14 kg/ha. The longer rain-free interval required for optimum control of green foxtail compared to Japanese millet may reflect a slower rate of herbicide absorption in green foxtail.
Waterhemp has emerged as one of the most problematic weeds in agronomic crops in the Midwest beca... more Waterhemp has emerged as one of the most problematic weeds in agronomic crops in the Midwest because of an extended germination period and widespread occurrence of biotypes resistant to atrazine and sulfonylurea herbicides. However, the competitive effects of late-emerging cohorts on corn yield are not known. Field studies were conducted in 2001 and 2002 at Columbia, Novelty, and Albany, MO, to determine the effects of late-emerging waterhemp interference on corn growth, nitrogen (N) accumulation, and yield. Waterhemp emerged approximately 20 d after planting (DAP) and was treated at heights of 8, 15, 23, 31, 38, or 46 cm with directed applications of dicamba + diflufenzopyr followed by hand hoeing. Soil water status, corn leaf chlorophyll content, and corn and common waterhemp height were recorded at the time of waterhemp removal. N stress was detected with a chlorophyll meter at four of six removal timings at high waterhemp densities (362 or more plants/m2) but only at one of six removal timings at lower densities (82 or less plants/m2). Water stress was observed at five of the six removal timings at high densities but at none of the removal timings at low densities. High waterhemp densities reduced corn yield when allowed to reach 15 cm before removal, and yields were reduced 36% when not controlled. At low densities, yield losses did not occur unless waterhemp was allowed to remain with corn season long. Our research suggests that waterhemp is less competitive with corn than redroot pigweed, smooth pigweed, and Palmer amaranth. In addition, low densities of late-emerging waterhemp would not warrant removal to protect corn yield.
Annual bluegrass is a pervasive weed on golf courses in the Transition Zone of the United States ... more Annual bluegrass is a pervasive weed on golf courses in the Transition Zone of the United States and is difficult to selectively remove. For years, superintendents have applied glyphosate on dormant zoysiagrass to remove cool-season weeds. In 2007, a population of annual bluegrass in Columbia, MO, was not controlled with glyphosate after more than 10 yr of continuous applications. Greenhouse studies were established to compare the response of suspect glyphosate-resistant (CCMO1) and -susceptible annual bluegrass to glyphosate. Seedling plants were treated with glyphosate from 0 to 6.27 kg ae ha−1. At 21 d after treatment, reductions in biomass for susceptible annual bluegrass reached a maximum at glyphosate rates of 0.78 kg ha−1or higher. Comparatively, the biomass of CCMO1 plants was only reduced by 50% at 0.78 kg ha−1, and reductions did not exceed 60% at rates up to 6.27 kg ha−1, which is eight times the labeled rate. At rates necessary to reduce plant dry weights by 50%, the resistance factor (RF) for CCMO1 was 5.2. Twenty-one days following biomass assessment, regrowth of plants was non-existent on susceptible plants at 0.78 kg ha−1glyphosate or above, but CCMO1 plants reached 1.7 cm regrowth at the 6.27 kg ha−1rate. Based on the regrowth, the RF for CCMO1 was 5.2. Results indicate a new species has been identified with resistance to glyphosate, and this represents the first report of glyphosate resistance in turfgrass.
ABSTRACT Absorption and translocation of three commercial formulations of glyphosate, the isoprop... more ABSTRACT Absorption and translocation of three commercial formulations of glyphosate, the isopropylamine salt formulated as Roundup Ultra™ (IPA1) and Roundup UltraMax™ (IPA2) and the diammonium salt formulated as Touchdown™ IQ (DA), were compared in three- to five-leaf velvetleaf, common waterhemp, and pitted morningglory. Absorption of 14C-glyphosate in velvetleaf was not significantly different among the three formulations up to 50 h after treatment (HAT). More absorption of 14C-glyphosate occurred in the IPA1 (26.0%) vs. the IPA2 (17.7%) formulation over 74 h. Of the total 14C-glyphosate absorbed, 20 to 35% was translocated from the treated leaf to the rest of the plant. Initial absorption of 14C-glyphosate was rapid in common waterhemp with the IPA1 (42.7%) and IPA2 (30.7%) formulations; both were higher compared with absorption of the DA formulation (11.5%) by 2 HAT. These differences continued up to 26 HAT, but no differences were evident by 74 HAT. Up to 65% of the 14C-glyphosate absorbed was translocated out of the treated leaf by 74 HAT, with roots the primary sink. Initial absorption of 14C-glyphosate was slow in pitted morningglory compared with the other species. More foliar absorption occurred in plants treated with the DA (13.6%) vs. the IPA2 formulation (4.9%) by 6 HAT. Absorption beyond 26 HAT was not different among the three glyphosate formulations. Translocation of 14C-glyphosate to roots was 27% greater as the DA salt than IPA1 and IPA2 by 74 HAT. The distribution pattern of glyphosate was similar in all species; phosphorimages demonstrated movement both acropetal and basipetal, with accumulation in roots greater than in any other plant parts. An efficacy study parallel to the 14C study showed no difference among the three glyphosate formulations on the species investigated at both 74 HAT and 2 wk after treatment. Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer AMATA; pitted morningglory, Ipomoea lacunosa L. IPOLA; velvetleaf, Abutilon theophrasti Medicus ABUTH.
Amaranthus species, commonly referred to as ''pigweeds,'' are among the most troublesome weeds in... more Amaranthus species, commonly referred to as ''pigweeds,'' are among the most troublesome weeds in many crop production systems. Effective control of these species often begins with an understanding of their biological and reproductive characteristics. At two sites in Missouri, six pigweed species (redroot pigweed, common waterhemp, spiny amaranth, tumble pigweed, smooth pigweed, and Palmer amaranth) were established in 60-m rows spaced 1.5 m apart. At biweekly intervals, plant heights and dry weights were recorded for each species; seed numbers were estimated at the end of the growing season. Dry weight of Palmer amaranth was up to 65% greater than those of all other species 2 wk after planting (WAP). Palmer amaranth biomass accumulation remained greater than those of the other species throughout the season and at the end of the season was 1.2-and 2.7-fold greater than those of redroot and tumble pigweed, respectively. Palmer amaranth was approximately 10 cm tall 2 WAP (37% taller than the next tallest species, redroot pigweed) and approximately 24 cm tall 4 WAP (45% taller than redroot pigweed). In contrast, common waterhemp had not emerged 2 WAP, and plant dry weight 4 WAP was approximately 11 and 26% those of Palmer amaranth and redroot pigweed, respectively. Final plant height ranged from 58 (tumble pigweed) to 208 cm (Palmer amaranth). Redroot pigweed, smooth pigweed, common waterhemp, and Palmer amaranth plants each produced over 250,000 seeds plant Ϫ1. Spiny amaranth and tumble pigweed produced approximately 114,000 and 50,000 seeds plant Ϫ1 , respectively. Common waterhemp produced 535 seeds g Ϫ1 of total plant dry weight; this seed production was 1.4-, 1.4-, 2.0-, 3.4-, and 3.4-fold greater than those of redroot pigweed, smooth pigweed, Palmer amaranth, tumble pigweed, and spiny amaranth, respectively. Because the timing for many postemergence herbicides depends on weed height, rapid growth shortly after emergence reduces the time frame for optimum control of species such as Palmer amaranth. Delayed emergence also could result in escaped common waterhemp. Escape of only a few plants could result in a rapid increase in seed populations in the soil seed bank and may select for late-emerging biotypes. Nomenclature: Common waterhemp, Amaranthus rudis Sauer AMATA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; redroot pigweed, Amaranthus retroflexus L. AMARE; smooth pigweed, Amaranthus hybridus L. AMACH; spiny amaranth, Amaranthus spinosus L. AMASP; tumble pigweed, Amaranthus albus L. AMAAL.
Journal of Agricultural and Food Chemistry, Dec 5, 2002
The estrogenic isoflavones of soybeans and their glycosides are products of the shikimate pathway... more The estrogenic isoflavones of soybeans and their glycosides are products of the shikimate pathway, the target pathway of glyphosate. This study tested the hypothesis that nonphytotoxic levels of glyphosate and other herbicides known to affect phenolic compound biosynthesis might influence levels of these nutraceutical compounds in glyphosate-resistant soybeans. The effects of glyphosate and other herbicides were determined on estrogenic isoflavones and shikimate in glyphosate-resistant soybeans from identical experiments conducted on different cultivars in Mississippi and Missouri. Four commonly used herbicide treatments were compared to a hand-weeded control. The herbicide treatments were (1) glyphosate at 1260 g/ha at 3 weeks after planting (WAP), followed by glyphosate at 840 g/ha at 6 WAP; (2) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied preemergence (PRE), followed by glyphosate at 1260 g/ha at 6 WAP; (3) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE, followed by glyphosate at 1260 g/ha at full bloom; and (4) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE, followed by acifluorfen at 280 g/ha plus bentazon at 560 g/ha plus clethodim at 140 g/ha at 6 WAP. Soybeans were harvested at maturity, and seeds were analyzed for daidzein, daidzin, genistein, genistin, glycitin, glycitein, shikimate, glyphosate, and the glyphosate degradation product, aminomethylphosphonic acid (AMPA). There were no remarkable effects of any treatment on the contents of any of the biosynthetic compounds in soybean seed from either test site, indicating that early and later season applications of glyphosate have no effects on phytoestrogen levels in glyphosate-resistant soybeans. Glyphosate and AMPA residues were higher in seeds from treatment 3 than from the other two treatments in which glyphosate was used earlier. Intermediate levels were found in treatments 1 and 2. Low levels of glyphosate and AMPA were found in treatment 4 and a hand-weeded control, apparently due to herbicide drift.
Field studies were established at two locations in Missouri to determine Amaranthus rudius (commo... more Field studies were established at two locations in Missouri to determine Amaranthus rudius (common waterhemp) control by single or multiple pre-emergence and/or postemergence herbicide strategies in glyphosate-resistant corn and soybean. The corn study assessed five herbicide strategies: pre-emergence alone; mid-postemergence alone; early postemergence followed by mid-postemergence; preemergence followed by mid-postemergence without glyphosate; and pre-emergence followed by glyphosate mid-postemergence. The soybean study assessed four herbicide strategies: mid-postemergence alone; early postemergence followed by mid-postemergence; preemergence followed by glyphosate mid-postemergence; and pre-emergence followed by mid-postemergence without glyphosate. In corn, pre-emergence herbicides suppressed A. rudius growth and development 7-34 days longer, compared to the untreated control. The strategies with single herbicide applications provided 21-99% control of A. rudius, while the multiple application strategies provided 84-100% control of A. rudius. In soybean, the presence of pre-emergence herbicides suppressed A. rudius emergence and growth for 7-31 days, compared to treatments with no herbicide application. A single herbicide application provided 69-100% control of A. rudius, and the multiple application strategies were more consistent with 77-100% control. Effective season-long management of A. rudius in glyphosate-resistant corn and soybean should include sequential herbicide applications.
A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in ... more A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in media containing the herbicide atrazine at concentrations up to 100-fold greater than the lethal concentration (1.0 {mu}M) for the unselected (wild type) cell line. The basis for atrazine resistance could not be identified by differential uptake or metabolism. Photosynthetic electron transport rates for both intact cell and isolated thylakoid membranes from chloroplasts were unaffected in variant cells at atrazine concentrations up to 100-fold greater than for wild type cells. Photoaffinity labeling of isolated thylakoid membranes from both cell lines with {sup 14}C-azidoatrazine revealed an altered Q{sub B} polypeptide in variant cells resulting in low or no affinity for atrazine. A portion of the chloroplast psbA gene, encoding the Q{sub B} polypeptide, was sequenced for both cell lines. The basis for atrazine resistance in variant cells was identified as a single base change resulting in the alteration of serine to threonine at position 264 of the Q{sub B} polypeptide. In addition to atrazine resistance, variant cells exhibit enhanced tolerance to the herbicides DCMU and metribuzin, but greater sensitivity to bentazon. No reductions in variant cell growth and photosynthetic efficiency in the absence of atrazine were observed.
A mutation of the psbA gene was identified in photoautotrophic potato (Solanum tuberosum 1. cv Su... more A mutation of the psbA gene was identified in photoautotrophic potato (Solanum tuberosum 1. cv Superior x U.S. Department of Agriculture line 66-142) cells selected for resistance to 6-chloro-N-ethyl-N'-(l-methylethyl)-l,3,5-triazine-2,4-diamine (atrazine). Photoaffinity labeling with 6-azido-N-ethyl-N'-(l-methyIethyl)-1,3,5-triazine-2,4-diamine detected a thylakoid membrane protein with a M. of 32,000 in susceptible, but not in resistant, cells. This protein was identified as the secondary quinone acceptor of photosystem II (QB) protein. Atrazine resistance in selected cells was attributable to a mutation from ACT (serine) to ACT (threonine) in codon 264 of the psbA gene that encodes the Q. protein. Although the mutant cells exhibited extreme levels of resistance to atrazine, no concomitant reductions in photosynthetic electron transport or cell growth rates compared to the unselected cells were detected. This is in contrast with the losses in productivity observed in atrazine-resistant mutants that contain a glycine-264 alteration. Prolonged agronomic use of PSII inhibitors, specifically striazine herbicides, has resulted in the evolution of resistant weed biotypes. The predominant basis for resistance is a single nucleotide substitution in the chloroplast psbA gene (Mazur and Falco, 1989), which encodes the D1 thylakoid protein (termed the Q B protein) and is the target molecule for s-triazine binding. In a11 resistant weed biotypes examined to date, the specific mutation is a G for A substitution that results in a change from Ser to Gly in position 264 of the mature QB protein (Blyden and Gray, 1986; Bettini et al., 1987; Barros and Dyer, 1988; Mazur and Falco, 1989). This mutation effectively eliminates s-triazine binding affinity to the protein. s-Triazine resistance has been stably transferred from weed to crop species by both interspecific (Ayotte et al., 1987) and somatic cell hybridization (Binding et al., 1982). Transgenic plants that express a nuclear gene encoding a modified Q B protein with a single peptide for chloroplast targeting of the protein also exhibited increased atrazine tolerance (Cheung et al., 1988). Incorporation of s-triazine resistance into crops Joumal paper No.
Juniper online journal of public health, Aug 15, 2023
Although dicamba can move long distances via off-target movement [5], significant damage to tomat... more Although dicamba can move long distances via off-target movement [5], significant damage to tomato, potato and watermelon has also been recorded at representative drift rates. [4] found that watermelon treated 20 days after planting (DAP) with 7.5 g ae ha-1 of the label rate of dicamba exhibited 40% visual injury and had vine lengths 49% the length of the non-treated
Journal of Agricultural and Food Chemistry, Mar 12, 2010
Greenhouse and laboratory experiments were conducted to investigate differences in glyphosate sus... more Greenhouse and laboratory experiments were conducted to investigate differences in glyphosate susceptibility among three species of the genus Conyza introduced as weeds in Spain: tall fleabane (Conyza sumatrensis), hairy fleabane (Conyza bonariensis), and horseweed (Conyza canadensis). Plant material was obtained from seeds collected in weed populations growing in olive groves and citrus orchards in southern Spain, with no previous history of glyphosate application. Dose-response curves displayed ED(50) values of 2.9, 15.7, and 34.9 g ai ha(-1), respectively, for C. sumatrensis, C. bonariensis, and C. canadensis plants at the rosette stage (6-8 leaves). Significant differences were found among the three species in the glyphosate retention on leaves as well as the leaf contact angle. The species order according to glyphosate retention was C. sumatrensis &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; C. bonariensis &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; C. canadensis, while the mean contact angles of glyphosate droplets were 59.2, 65.5, and 72.9 degrees , respectively. There were no significant differences among species in the absorption of [(14)C]glyphosate (ranged from 37.4% for C. canadensis to 52.4% for C. sumatrensis), but the order among species was the same as glyphosate retention. The amount of radioactivity translocated from treated leaves was lower in C. canadensis as compared to the other two species (C. sumatrensis &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; C. bonariensis &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; C. canadensis). Combined, all of the studied parameters identified differential susceptibility to glyphosate among the Conyza species. Each species accumulated shikimate in leaf tissues following application of glyphosate at 200 g ai ha(-1). However, C. canadensis exhibited lower shikimate levels than the other two species at 168 h after herbicide application. For hairy fleabane, a greenhouse study explored its susceptibility to glyphosate at three developmental stages: rosette, bolting (stem height, 10-15 cm), and flowering. The ED(50) was lower at the rosette stage (15.7 g ai ha(-1)) as compared to bolting (86.6 g ai ha(-1)), with the highest ED(50) values occurring at flowering (117.5 g ai ha(-1)); plants at the earlier developmental stage retained more glyphosate. These results agree with field observations that plants at early developmental stages are more sensitive to glyphosate.
A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in ... more A photoautotrophic potato cell line (variant) was isolated and is capable of sustained growth in media containing in the herbicide atrazine at concentration up to 100 x greater than the lethal concentration for the unselected (wild type) cell line (1.0 {mu}M). Fresh weight doubling times of variant cells in the presence or absence of 1.0 {mu}M atrazine were identical to wild type cells grown in the absence of atrazine. Maintenance of variant cells up to 10 passages in the absence of atrazine resulted in a reduction in the concentration of atrazine necessary to inhibit fresh weight gain by 99% (ID{sub 99}) from 100 to 80 {mu}M. Comparison of {sup 14}C-atrazine uptake indicated wild type cells accumulated up to 2.5-fold more atrazine than varient cells within 72h of exposure but no differences were detected thereafter. Electron transport of both isolated chloroplasts and intact cells were significantly inhibited in the wild type cell line by 1.0 {mu}M atrazine but unaffected in the variant cell line by atrazine concentrations up to 10 {mu}M. After 30 days in the presence of 1.0 {mu}M atrazine, wild type cells did not significantly metabolize atrazine, however, variant cells reduced atrazine concentrations to <0.05 {mu}M regardless if themore » initial atrazine concentration was 1.0 or 10.0 {mu}M. Both metabolism of atrazine and alterations within the chloroplast (potentially a reduction in atrazine binding affinity) appear to be important components of tolerance within variant cells.« less
Windmillgrass (Chloris verticillata Nutt.) is spreading from native areas, becoming problematic i... more Windmillgrass (Chloris verticillata Nutt.) is spreading from native areas, becoming problematic in established turf in Missouri, and surrounding states. Limited information is available regarding post-emergence (POST) control options for turf. The objective of this research was to assess the visual and biomass response of windmillgrass to selected herbicides approved for use in turf. In one study, a greenhouse experiment was conducted with POST application of seven selected herbicides, including dimethylamine salt of quinclorac, fenoxaprop-P-ethyl, foramsulfuron, mesotrione, sulfentrazone, and topramezone in a tank-mixture with triclopyr, as well as a pre-packed product containing thiencarbazone-methyl, foramsulfuron, and halosulfuron-methyl. Under the same experimental conditions, five additional treatments, including mesotrione or topramezone applied at label-suggested rates alone or in combination with triclopyr, in addition to triclopyr alone, were applied to a second study on tillering windmillgrass. At 4 weeks after treatment (WAT), only fenoxaprop-p-ethyl consistently resulted in a complete control of windmillgrass. No measurable regrowth of plants was observed two weeks following the initial collection of windmillgrass aboveground biomass. In the second study, combinations of mesotrione and topramezone with triclopyr resulted in 100% visual injury of windmillgrass at 4 WAT; mesotrione and topramezone alone only resulted in up to 66% visual injury. Triclopyr alone resulted in 91% injury at 4 WAT. The greatest reduction of windmillgrass biomass and least amount of regrowth resulted from mesotrione and topramezone combinations with triclopyr. Control of windmillgrass is effective with fenoxaprop-P-ethyl alone, but use of a 4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor such as mesotrione and topramezone should include the addition of triclopyr.
weed in the pigweed family that is found throughout the Midwest. Waterhemp seedlings have oar-sha... more weed in the pigweed family that is found throughout the Midwest. Waterhemp seedlings have oar-shaped or oval cotyledons (seed leaves) and are hairless (Figure 1), unlike redroot or smooth pigweed. Mature waterhemp plants have long, lance-shaped leaves that are waxy or glossy in appearance (Figure 2). Plants can range in height from 4 inches to 12 feet depending on growing conditions, and they can grow as much as 1 inch per day during the summer growing season. In surveys conducted in Illinois and Missouri, producers and agricultural retailers listed waterhemp as one of the most common and troublesome weeds encountered in soybean production. Waterhemp is a prolific seed producer, capable of producing about one-and-a-half times more seed than most other pigweed species. Waterhemp plants generally produce about 250,000 seeds per plant, although some plants can produce as many as 1 million seeds when growing under optimal conditions in noncompetitive environments. Waterhemp seeds have a discontinuous emergence pattern and can germinate later in the season than most summer annual weed species. This allows waterhemp to escape many preemergence (PRE) herbicide applications and often allows this weed to flourish after postemergence (POST) applications of nonresidual herbicides like glyphosate (sold as Roundup or a variety of other trade names). Waterhemp seed can also persist in the soil for as many as four years with 95 percent of the seed remaining viable after this time.
Palmer amaranth (Amaranthus palmeriS. Watson) is a problematic weed encountered in U.S. cotton (G... more Palmer amaranth (Amaranthus palmeriS. Watson) is a problematic weed encountered in U.S. cotton (Gossypium hirsutumL.) and soybean [Glycine max(L.) Merr.] production, with infestations spreading northward. This research investigated the influence of planting date (early, mid-, and late season) and population (AR, IN, MO, MS, NE, and TN) onA. palmerigrowth and reproduction at two locations. All populations planted early or midseason at Throckmorton Purdue Agricultural Center (TPAC) and Arkansas Agriculture Research and Extension Center (AAREC) measured 196 and 141 cm or more, respectively. Amaranthus palmeriheight did not exceed 168 and 134 cm when planted late season at TPAC and AAREC, respectively. Early season plantedA. palmerifrom NE grew to 50% of maximum height 8 to 13 d earlier than all other populations under TPAC conditions. In addition, the NE population planted early, mid-, and late season achieved 50% inflorescence emergence 5, 4, and 6 d earlier than all other populations, respectively. All populations established at TPAC produced fewer than 100,000 seeds plant−1. No population planted at TPAC and AAREC produced more than 740 and 1,520 g plant−1of biomass at 17 and 19 wk after planting, respectively. Planting date influenced the distribution of male and female plants at TPAC, but not at AAREC. Amaranthus palmerifrom IN and MS planted late season had male-to-female plant ratios of 1.3:1 and 1.7:1, respectively. Amaranthus palmeriintroduced to TPAC from NE can produce up to 7,500 seeds plant−1if emergence occurs in mid-July. An NEA. palmeripopulation exhibited biological characteristics allowing it to be highly competitive if introduced to TPAC due to a similar latitudinal range, but was least competitive when introduced to AAREC. AlthoughA. palmerioriginating from different locations can vary biologically, plants exhibited environmental plasticity and could complete their life cycle and contribute to spreading populations.
Variability in glyphosate efficacy has been observed following late day field applications, but t... more Variability in glyphosate efficacy has been observed following late day field applications, but the influence of this “time-of-day effect” on weed control and soybean yield is unknown. Additionally, the basis for differences in weed control due to application time of day has not been fully elucidated. In field trials, broadleaf weed biomass was ≥5-fold greater when glyphosate was applied at 6:00 A.M. compared to 6:00 P.M. in three of four site–years. No consistent time-of-day effect was observed on treated grass weeds. Soybean yield was unaffected by treatments, and was similar to the weed-free control. In a greenhouse study, both barnyardgrass and velvetleaf biomass were as much as 25 to 80% greater when glyphosate was applied at 8:00 P.M. vs. 2:00 P.M. Examination of individual components of the time-of-day effect for velvetleaf indicated that leaf angle and time of application accounted for 82 and 18%, respectively, of the biomass change. This research suggests that diurnal changes in leaf movement of velvetleaf account for much of the time-of-day effect, with the remainder likely due to an unknown physiological component.
Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and w... more Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and weed control with glufosinate alone or combined with quizalofop, lactofen, imazethapyr, flumiclorac, or bentazon plus acifluorfen in narrow-row, glufosinate-resistant soybean. Soybean injury ranged from 0 to 21% at 2 wk after treatment (WAT) and from 0 to 5% by 4 WAT. Glufosinate alone at 0.29 and 0.4 kg ai/ha controlled velvetleaf, common waterhemp, common ragweed, morningglory species, and giant foxtail greater than 85% in all studies. Mixtures containing glufosinate and other herbicides controlled these species greater than 81% but did not improve control over glufosinate alone. Estimates of weed biomass closely reflected visual control evaluations. However, giant foxtail biomass was higher for mixtures of glufosinate plus lactofen, flumiclorac, or bentazon and acifluorfen, indicating possible antagonism of glufosinate activity. At both locations, soybean yields were similar among most treatments, but that of the glufosinate plus lactofen treatment was lower when compared with other treatments. Additional trials evaluated soybean response and weed control with a preemergence herbicide followed by glufosinate postemergence (POST), glufosinate applied once or twice POST, and mixtures of glufosinate plus imazethapyr or flumiclorac POST in wide-row soybean. Glufosinate applied twice controlled common waterhemp, morningglory species, prickly sida, common cocklebur, and giant foxtail up to 39% greater than did glufosinate applied once. The addition of imazethapyr, but not flumiclorac, to glufosinate improved weed control when compared with glufosinate alone.
Journal of Agricultural and Food Chemistry, Oct 1, 1995
Interaction between a herbicide and plant residue on the soil surface in plant residue management... more Interaction between a herbicide and plant residue on the soil surface in plant residue management systems such as no-tillage or cover crop is of interest in terms of environmental fate of the herbicide. This study was designed to evaluate sorption and desorption of chlorimuron ethyl {ethyl 2-[[[[(4chloro-6-methoxy-2-pyrimidinyl)aminolc~bonyll~olsulfonyllbenzoic acid} in herbicide-desiccated rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) residues and soils collected from a field. Sorption was determined by reacting 0.5 g of soil or plant residue with 6 mL of [14Clchlorimuron ethyl solution at five concentrations (0.06-12.04 pmol L-l) for 72 h. Freundlich Kf was highest in hairy vetch (6.33) followed by rye (3.95) and soils from no cover crop or beneath plant residue (0.81-1.03). The N values (0.88-0.95) for soils and plant residues indicated nearly linear sorption. Time course sorption data analyzed by an equilibriumnetic model indicated that sorption was initially rapid (within 1 h), followed by a negligible increase in soil or a slow increase in rye and hairy vetch residue. Chlorimuron ethyl Kf increased with increased decomposition of plant residue. The Kf for rye and hairy vetch residues sampled at 11 weeks after soybean planting increased by 54 and 49%, respectively, compared with residues sampled at planting. CaCl2-desorbable chlorimuron ethyl in two consecutive 24-h cycles ranged from 54 to 65% in soils and from 42 to 49% of that sorbed in plant residues. Two additional 24-h cycles with methanol/(NH&C03 did not completely desorb the remaining chlorimuron ethyl. Under field conditions, plant residues can apparently intercept and temporarily retain chlorimuron ethyl.
Undesirable stands of hybrid corn often result in a decision to replant; removal of the initial c... more Undesirable stands of hybrid corn often result in a decision to replant; removal of the initial corn is recommended to reduce competition for available resources. Because much of the hybrid corn is glyphosate-resistant (GR), the particular herbicide and timing for control is challenging. No-till field trials were established in central and northeast Missouri in 2009 and 2010 to determine the efficacy of glufosinate POST in glufosinate-resistant corn or imazethapyr plus imazapyr POST in imidazolinone-resistant corn for the control of GR corn. Separate blocks of glufosinate-resistant and imidazolinone-resistant corn were planted in 76 cm rows, with GR corn established between rows at densities of 1 (low) and 4 (high) plants m−2. Herbicides were broadcast at corn heights of 10, 20, and 40 cm. Visual estimates of control rated 5 wk after treatment were highest for the 20 cm application height, ranging from 81 to 84% and 72 to 79% with glufosinate or imazethapyr plus imazapyr, respectively. Control was unacceptable at 10 and 40 cm, ranging from 26 to 62% and 24 to 83%. Dry weights per plant indicated that applications at all heights reduced GR corn biomass a minimum of 94 and 82% with glufosinate or imazethapyr plus imazapyr, respectively. Although control of GR corn with single applications of glufosinate and imazethapyr plus imazapyr was unacceptable for two of three application heights, reductions in corn biomass indicate applications were effective.
Over the past 30 years, numerous reports on herbicide resistance have been published. Although re... more Over the past 30 years, numerous reports on herbicide resistance have been published. Although research in this area is still in its infancy compared to the research done on insecticide and fungicide resistance, there are now more than 80 different plant species worldwide that have developed resistance to one or more herbicides. Mechanisms of herbicide resistance include metabolic detoxification, structural changes in the herbicide’s target site, alterations in the uptake, translocation, or compartmentalization of a herbicide. Although all of these modifications resulting in herbicide resistance in plants have been documented, alteration in the target site is the most common one and provides the highest level of resistance. Resistance has been shown to occur against all major herbicide classes. This chapter will review resistance to all major groups of herbicides, based on mode of action. The appearance of resistance is most likely in monoculture situations in which a herbicide or herbicides with the same mode of action are used continuously. One alarming trend is the emergence of weed species with resistance to herbicides with more than one site of action. This can occur as a result of either some mechanism of metabolic detoxification which degrades many herbicides or alterations in different herbicide target sites, or some combination of both of these mechanisms. Since the world has become very much dependent on herbicides for keeping weeds under control, additional reports on herbicide resistance are urgently needed.
Field experiments were initiated to determine the efficacy of fluazifop as influenced by growth s... more Field experiments were initiated to determine the efficacy of fluazifop as influenced by growth stage for green, yellow, and giant foxtail, large crabgrass, and Japanese millet. Additionally, the influence of air temperature and simulated rainfall on fluazifop efficacy for green foxtail and Japanese millet was determined by greenhouse and growth-room experiments. In both 1983 and 1984, fluazifop activity was reduced as the growth stage increased from 3- to 5- to 7-leaf for all species. Significant differences among species in susceptibility to fluazifop were evident with the descending order of tolerance: green foxtail &gt; large crabgrass &gt; yellow foxtail &gt; giant foxtail &gt; Japanese millet. Increasing the air temperature from 18 to 30 C reduced fluazifop control of green foxtail at herbicide rates less than 0.14 kg ai/ha but did not affect Japanese millet. A 1- to 2-h rain-free interval was required for optimum control of green foxtail and Japanese millet at 0.07 kg/ha fluazifop; the interval was reduced to 45 and 15 min, respectively, when fluazifop rates were 0.14 kg/ha. The longer rain-free interval required for optimum control of green foxtail compared to Japanese millet may reflect a slower rate of herbicide absorption in green foxtail.
Waterhemp has emerged as one of the most problematic weeds in agronomic crops in the Midwest beca... more Waterhemp has emerged as one of the most problematic weeds in agronomic crops in the Midwest because of an extended germination period and widespread occurrence of biotypes resistant to atrazine and sulfonylurea herbicides. However, the competitive effects of late-emerging cohorts on corn yield are not known. Field studies were conducted in 2001 and 2002 at Columbia, Novelty, and Albany, MO, to determine the effects of late-emerging waterhemp interference on corn growth, nitrogen (N) accumulation, and yield. Waterhemp emerged approximately 20 d after planting (DAP) and was treated at heights of 8, 15, 23, 31, 38, or 46 cm with directed applications of dicamba + diflufenzopyr followed by hand hoeing. Soil water status, corn leaf chlorophyll content, and corn and common waterhemp height were recorded at the time of waterhemp removal. N stress was detected with a chlorophyll meter at four of six removal timings at high waterhemp densities (362 or more plants/m2) but only at one of six removal timings at lower densities (82 or less plants/m2). Water stress was observed at five of the six removal timings at high densities but at none of the removal timings at low densities. High waterhemp densities reduced corn yield when allowed to reach 15 cm before removal, and yields were reduced 36% when not controlled. At low densities, yield losses did not occur unless waterhemp was allowed to remain with corn season long. Our research suggests that waterhemp is less competitive with corn than redroot pigweed, smooth pigweed, and Palmer amaranth. In addition, low densities of late-emerging waterhemp would not warrant removal to protect corn yield.
Annual bluegrass is a pervasive weed on golf courses in the Transition Zone of the United States ... more Annual bluegrass is a pervasive weed on golf courses in the Transition Zone of the United States and is difficult to selectively remove. For years, superintendents have applied glyphosate on dormant zoysiagrass to remove cool-season weeds. In 2007, a population of annual bluegrass in Columbia, MO, was not controlled with glyphosate after more than 10 yr of continuous applications. Greenhouse studies were established to compare the response of suspect glyphosate-resistant (CCMO1) and -susceptible annual bluegrass to glyphosate. Seedling plants were treated with glyphosate from 0 to 6.27 kg ae ha−1. At 21 d after treatment, reductions in biomass for susceptible annual bluegrass reached a maximum at glyphosate rates of 0.78 kg ha−1or higher. Comparatively, the biomass of CCMO1 plants was only reduced by 50% at 0.78 kg ha−1, and reductions did not exceed 60% at rates up to 6.27 kg ha−1, which is eight times the labeled rate. At rates necessary to reduce plant dry weights by 50%, the resistance factor (RF) for CCMO1 was 5.2. Twenty-one days following biomass assessment, regrowth of plants was non-existent on susceptible plants at 0.78 kg ha−1glyphosate or above, but CCMO1 plants reached 1.7 cm regrowth at the 6.27 kg ha−1rate. Based on the regrowth, the RF for CCMO1 was 5.2. Results indicate a new species has been identified with resistance to glyphosate, and this represents the first report of glyphosate resistance in turfgrass.
ABSTRACT Absorption and translocation of three commercial formulations of glyphosate, the isoprop... more ABSTRACT Absorption and translocation of three commercial formulations of glyphosate, the isopropylamine salt formulated as Roundup Ultra™ (IPA1) and Roundup UltraMax™ (IPA2) and the diammonium salt formulated as Touchdown™ IQ (DA), were compared in three- to five-leaf velvetleaf, common waterhemp, and pitted morningglory. Absorption of 14C-glyphosate in velvetleaf was not significantly different among the three formulations up to 50 h after treatment (HAT). More absorption of 14C-glyphosate occurred in the IPA1 (26.0%) vs. the IPA2 (17.7%) formulation over 74 h. Of the total 14C-glyphosate absorbed, 20 to 35% was translocated from the treated leaf to the rest of the plant. Initial absorption of 14C-glyphosate was rapid in common waterhemp with the IPA1 (42.7%) and IPA2 (30.7%) formulations; both were higher compared with absorption of the DA formulation (11.5%) by 2 HAT. These differences continued up to 26 HAT, but no differences were evident by 74 HAT. Up to 65% of the 14C-glyphosate absorbed was translocated out of the treated leaf by 74 HAT, with roots the primary sink. Initial absorption of 14C-glyphosate was slow in pitted morningglory compared with the other species. More foliar absorption occurred in plants treated with the DA (13.6%) vs. the IPA2 formulation (4.9%) by 6 HAT. Absorption beyond 26 HAT was not different among the three glyphosate formulations. Translocation of 14C-glyphosate to roots was 27% greater as the DA salt than IPA1 and IPA2 by 74 HAT. The distribution pattern of glyphosate was similar in all species; phosphorimages demonstrated movement both acropetal and basipetal, with accumulation in roots greater than in any other plant parts. An efficacy study parallel to the 14C study showed no difference among the three glyphosate formulations on the species investigated at both 74 HAT and 2 wk after treatment. Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer AMATA; pitted morningglory, Ipomoea lacunosa L. IPOLA; velvetleaf, Abutilon theophrasti Medicus ABUTH.
Amaranthus species, commonly referred to as ''pigweeds,'' are among the most troublesome weeds in... more Amaranthus species, commonly referred to as ''pigweeds,'' are among the most troublesome weeds in many crop production systems. Effective control of these species often begins with an understanding of their biological and reproductive characteristics. At two sites in Missouri, six pigweed species (redroot pigweed, common waterhemp, spiny amaranth, tumble pigweed, smooth pigweed, and Palmer amaranth) were established in 60-m rows spaced 1.5 m apart. At biweekly intervals, plant heights and dry weights were recorded for each species; seed numbers were estimated at the end of the growing season. Dry weight of Palmer amaranth was up to 65% greater than those of all other species 2 wk after planting (WAP). Palmer amaranth biomass accumulation remained greater than those of the other species throughout the season and at the end of the season was 1.2-and 2.7-fold greater than those of redroot and tumble pigweed, respectively. Palmer amaranth was approximately 10 cm tall 2 WAP (37% taller than the next tallest species, redroot pigweed) and approximately 24 cm tall 4 WAP (45% taller than redroot pigweed). In contrast, common waterhemp had not emerged 2 WAP, and plant dry weight 4 WAP was approximately 11 and 26% those of Palmer amaranth and redroot pigweed, respectively. Final plant height ranged from 58 (tumble pigweed) to 208 cm (Palmer amaranth). Redroot pigweed, smooth pigweed, common waterhemp, and Palmer amaranth plants each produced over 250,000 seeds plant Ϫ1. Spiny amaranth and tumble pigweed produced approximately 114,000 and 50,000 seeds plant Ϫ1 , respectively. Common waterhemp produced 535 seeds g Ϫ1 of total plant dry weight; this seed production was 1.4-, 1.4-, 2.0-, 3.4-, and 3.4-fold greater than those of redroot pigweed, smooth pigweed, Palmer amaranth, tumble pigweed, and spiny amaranth, respectively. Because the timing for many postemergence herbicides depends on weed height, rapid growth shortly after emergence reduces the time frame for optimum control of species such as Palmer amaranth. Delayed emergence also could result in escaped common waterhemp. Escape of only a few plants could result in a rapid increase in seed populations in the soil seed bank and may select for late-emerging biotypes. Nomenclature: Common waterhemp, Amaranthus rudis Sauer AMATA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; redroot pigweed, Amaranthus retroflexus L. AMARE; smooth pigweed, Amaranthus hybridus L. AMACH; spiny amaranth, Amaranthus spinosus L. AMASP; tumble pigweed, Amaranthus albus L. AMAAL.
Journal of Agricultural and Food Chemistry, Dec 5, 2002
The estrogenic isoflavones of soybeans and their glycosides are products of the shikimate pathway... more The estrogenic isoflavones of soybeans and their glycosides are products of the shikimate pathway, the target pathway of glyphosate. This study tested the hypothesis that nonphytotoxic levels of glyphosate and other herbicides known to affect phenolic compound biosynthesis might influence levels of these nutraceutical compounds in glyphosate-resistant soybeans. The effects of glyphosate and other herbicides were determined on estrogenic isoflavones and shikimate in glyphosate-resistant soybeans from identical experiments conducted on different cultivars in Mississippi and Missouri. Four commonly used herbicide treatments were compared to a hand-weeded control. The herbicide treatments were (1) glyphosate at 1260 g/ha at 3 weeks after planting (WAP), followed by glyphosate at 840 g/ha at 6 WAP; (2) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied preemergence (PRE), followed by glyphosate at 1260 g/ha at 6 WAP; (3) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE, followed by glyphosate at 1260 g/ha at full bloom; and (4) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE, followed by acifluorfen at 280 g/ha plus bentazon at 560 g/ha plus clethodim at 140 g/ha at 6 WAP. Soybeans were harvested at maturity, and seeds were analyzed for daidzein, daidzin, genistein, genistin, glycitin, glycitein, shikimate, glyphosate, and the glyphosate degradation product, aminomethylphosphonic acid (AMPA). There were no remarkable effects of any treatment on the contents of any of the biosynthetic compounds in soybean seed from either test site, indicating that early and later season applications of glyphosate have no effects on phytoestrogen levels in glyphosate-resistant soybeans. Glyphosate and AMPA residues were higher in seeds from treatment 3 than from the other two treatments in which glyphosate was used earlier. Intermediate levels were found in treatments 1 and 2. Low levels of glyphosate and AMPA were found in treatment 4 and a hand-weeded control, apparently due to herbicide drift.
Field studies were established at two locations in Missouri to determine Amaranthus rudius (commo... more Field studies were established at two locations in Missouri to determine Amaranthus rudius (common waterhemp) control by single or multiple pre-emergence and/or postemergence herbicide strategies in glyphosate-resistant corn and soybean. The corn study assessed five herbicide strategies: pre-emergence alone; mid-postemergence alone; early postemergence followed by mid-postemergence; preemergence followed by mid-postemergence without glyphosate; and pre-emergence followed by glyphosate mid-postemergence. The soybean study assessed four herbicide strategies: mid-postemergence alone; early postemergence followed by mid-postemergence; preemergence followed by glyphosate mid-postemergence; and pre-emergence followed by mid-postemergence without glyphosate. In corn, pre-emergence herbicides suppressed A. rudius growth and development 7-34 days longer, compared to the untreated control. The strategies with single herbicide applications provided 21-99% control of A. rudius, while the multiple application strategies provided 84-100% control of A. rudius. In soybean, the presence of pre-emergence herbicides suppressed A. rudius emergence and growth for 7-31 days, compared to treatments with no herbicide application. A single herbicide application provided 69-100% control of A. rudius, and the multiple application strategies were more consistent with 77-100% control. Effective season-long management of A. rudius in glyphosate-resistant corn and soybean should include sequential herbicide applications.
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