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1
Berry, Adrian D., William M. Stall, B. Rathinasabapathi, Gregory E. Macdonald, and R. Charudattan. "Aggressivity: Cucumber vs. Amaranth." Weed Technology 20, no. 4 (2006): 986–91. http://dx.doi.org/10.1614/wt-04-270.1.
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A replacement series study was conducted to describe the aggressivity between cucumber, smooth pigweed, and livid amaranth. Cucumber was three times more competitive than smooth pigweed or livid amaranth, under the conditions of this study. However, there was equal competition and no antagonism between smooth pigweed and livid amaranth. Where cucumbers were planted in mixture with either of the two weeds, the relative yield total values were approximately 10 to 20% higher than the monocultures. Cucumber was a superior competitor when grown in mixture with smooth pigweed or livid amaranth, and the following aggressivity hierarchy exists: cucumber > livid amaranth = smooth pigweed. Results from the additive field study indicated that amaranth dry weights were significantly affected by smooth pigweed and livid amaranth density. Dry weight of amaranth was decreased by 48% at Gainesville and 25% at Live Oak, at 18 plants/m2. Despite differences between the Gainesville and Live Oak results, the dry weight data were similar for both smooth pigweed and livid amaranth at each location.
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Collins, Amanda S., Carlene A. Chase, William M. Stall, and Chad M. Hutchinson. "Optimum Densities of Three Leguminous Cover Crops for Suppression of Smooth Pigweed (Amaranthus hybridus)." Weed Science 56, no. 5 (2008): 753–61. http://dx.doi.org/10.1614/ws-07-101.1.
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Additive experiments were performed to determine optimum densities for nematode-suppressive cover crops to extend the benefit from the cover crops by also using them for weed suppression. In a preliminary experiment in 2002, a range of cover-crop densities was evaluated in mixtures with smooth pigweed at 5 plants m−2. Smooth pigweed biomass accumulation was suppressed by cowpea, sunn hemp, and velvetbean at the lowest cover-crop populations (38, 44, and 15 plants m−2, respectively). Based on these results, experiments were conducted in 2003 at two locations to examine the effects of lower cover-crop densities on a higher smooth pigweed population density of 15 plants m−2. Cowpea and velvetbean densities ranged from 10 to 50 plants m−2 and sunn hemp from 20 to 100 plants m−2. In 2003, cowpea density had no effect on smooth pigweed biomass. However, smooth pigweed biomass declined linearly by 51% as sunn hemp density increased to 100 plants m−2. Similarly, as velvetbean densities increased, smooth pigweed biomass decreased showing a linear response at one location and quadratic response at the second location. Maximum suppression of smooth pigweed biomass by velvetbean occurred at the highest cover-crop density (50 plants m−2). Excellent suppression of smooth pigweed at 5 plants m−2 or fewer will result in densities of 38, 44, and 15 plants m−2 of cowpea, sunn hemp, and velvetbean. However, with smooth pigweed at 15 plants m−2, optimum cover-crop densities were not obtained because no suppression was obtained with cowpea, and the lowest weed biomass with sunn hemp and velvetbean occurred with the highest densities used. Therefore, when high smooth pigweed densities are expected, sunn hemp and velvetbean should be used at densities greater than 100 and 50 plants m−2, respectively, and further study with higher densities will be needed to define optima.
3
Berry, Adrian D., William M. Stall, B. Rathinasabapathi, Gregory E. Macdonald, and R. Charudattan. "Smooth Pigweed (Amaranthus hybridusL.) and Livid Amaranth (Amaranthus lividus) Interference with Cucumber (Cucumis sativus)." Weed Technology 20, no. 1 (2006): 227–31. http://dx.doi.org/10.1614/wt-04-239r.1.
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Field studies were conducted to determine the effect of season-long interference of smooth pigweed or livid amaranth on the shoot dry weight and fruit yield of cucumber. Smooth pigweed or livid amaranth densities as low as 1 to 2 weeds per m2caused a 10% yield reduction in cucumber. The biological threshold of smooth pigweed or livid amaranth with cucumber is between 6 to 8 weeds per m2. Consequently, weed interference resulted in a reduction in cucumber fruit yield. Smooth pigweed, livid amaranth, and cucumber plant dry weight decreased as weed density increased. Evaluation of smooth pigweed, livid amaranth, and cucumber mean dry weights in interspecific competition studies indicated that cucumber reduced the dry weight of both species of amaranths.
4
Trader, Brian W., Henry P. Wilson, E. Scott Hagood, and Thomas E. Hines. "Halosulfuron Resistance in Smooth Pigweed (Amaranthus hybridus) Populations." Weed Technology 23, no. 3 (2009): 460–64. http://dx.doi.org/10.1614/wt-08-115.1.
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Greenhouse experiments were conducted to evaluate the response to halosulfuron of several smooth pigweed populations that had been shown to be resistant to acetolactate synthase (ALS, EC 2.2.1.6)-inihibiting herbicides. Five ALS-resistant smooth pigweed populations (R1, R2, R3, R4, and R5) and one susceptible (S) population were treated with halosulfuron POST at 0.27, 2.7, 27, 270, and 2,700 g ai/ha. Percentage injury and dry weight were used to determine resistance of smooth pigweed populations to halosulfuron. Populations of smooth pigweed with previous reports of resistance to ALS-inhibiting herbicides showed varying degrees of resistance to halosulfuron compared with the susceptible population. Concentrations of halosulfuron required to reduce ALS-resistant smooth pigweed dry weights 50% were 2 to 12-fold higher than that of the susceptible population. One population, designated R2, had increased resistance to halosulfuron applications, requiring 97 g/ha halosulfuron to reduce shoot dry weight 50% compared with only 8 g/ha for S. Our results show that populations of smooth pigweed with a history of ALS-inhibiting resistance can have differing degrees of resistance to halosulfuron.
5
Manley, Brian S., Henry P. Wilson, and Thomas E. Hines. "Smooth Pigweed (Amaranthus hybridus) and Livid Amaranth (A. lividus) Response to Several Imidazolinone and Sulfonylurea Herbicides." Weed Technology 10, no. 4 (1996): 835–41. http://dx.doi.org/10.1017/s0890037x00040884.
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The effects of chlorimuron, imazaquin, imazethapyr, nicosulfuron, primisulfuron, and thifensulfuron were evaluated on a population of smooth pigweed in Painter, VA with no history of treatment with acetolactate synthase (ALS)-inhibitor herbicides. Imazethapyr and nicosulfuron gave the greatest smooth pigweed control, and subsequently were used in field and greenhouse studies to investigate susceptibility of smooth pigweed and livid amaranth populations to ALS-inhibitor herbicides. Approximately 5 million smooth pigweed plants from Painter were treated with imazethapyr or nicosulfuron from 1992 to 1994 and no ALS-inhibitor-resistant plants were identified. In the greenhouse, the response of smooth pigweed from Painter, VA, Marion, MD, and Oak Hall, VA and livid amaranth from Warren County, NJ to imazaquin or imazethapyr and nicosulfuron was investigated. Smooth pigweed from Marion and Oak Hall and livid amaranth from NJ had histories of treatment with ALS-inhibitors. Painter smooth pigweed control was 81 to 97% by imazethapyr and nicosulfuron while control of the Marion and Oak Hall populations was 3 and 18% by imazaquin at 560 and 1120 g ai/ha, respectively, and control by nicosulfuron at 35 g ai/ha was 50 to 73%. Control of livid amaranth from Warren County, NJ was 8 to 15% by imazethapyr at 560 g ai/ha, and was 30 to 58% by nicosulfuron at 35 g/ha.
6
Toler, Joe E., J. Bradley Guice, and Edward C. Murdock. "Interference Between Johnsongrass (Sorghum halepense), Smooth Pigweed (Amaranthus hybridus), and Soybean (Glycine max)." Weed Science 44, no. 2 (1996): 331–38. http://dx.doi.org/10.1017/s0043174500093966.
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Competitive relationships between johnsongrass, smooth pigweed, and soybean were examined in 1986 and 1987, and the adequacy of an additive response model (ARM) and product response model (PRM) in predicting yield reductions due to multispecies weed populations was assessed. A severe drought reduced soybean yields statewide in 1986, whereas ideal conditions for soybean production were experienced in 1987. Averaged over monospecific weed densities of 1, 2, 4, and 8 plants 4.6 m−1of row, smooth pigweed intercepted 2.5 and 1.8 times more light than johnsongrass in 1986 and 1987, respectively. In multispecies populations having either 4 or 8 smooth pigweed plants 4.6 m−1of row, light interception by johnsongrass was negligible. Averaged over monospecific weed densities, smooth pigweed produced 5160 and 1760 kg ha−1, while johnsongrass produced 1530 and 450 kg ha−1dry weight in 1986 and 1987, respectively. In multispecies populations, smooth pigweed contributed more than 80% of the total weed biomass. As monospecific johnsongrass density increased, reductions in soybean seed yield were linear, whereas exponential response patterns adequately characterized reductions in soybean seed yield due to smooth pigweed interference. Based on calibrated monospecific responses, the ARM and PRM generally projected higher soybean seed yield reductions for multispecies weed populations than were observed. When crop production conditions were favorable and competitive effects of weeds were low, both models adequately predicted soybean seed yield reductions. When dry conditions unfavorable for crop production existed, the PRM best accommodated the interactive effects between johnsongrass, smooth pigweed, and soybean.
7
Santos, Bielinski M., Joan A. Dusky, William M. Stall, Donn G. Shilling, and Thomas A. Bewick. "Phosphorus effects on competitive interactions of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) with lettuce (Lactuca sativa)." Weed Science 46, no. 3 (1998): 307–12. http://dx.doi.org/10.1017/s0043174500089463.
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Replacement series studies were conducted under controlled conditions to determine the effect of phosphorus (P) rates and population densities on the competitiveness of smooth pigweed and common purslane with lettuce. Densities were 2, 4, and 8 plants per 113 cm2, whereas P rates were 0, 0.4, and 0.8 g PL−1soil. A P-deficient Histosol (0.3 mg water-extractable P L−1soil) was used. High P fertility enhanced the competitive ability of lettuce in smooth pigweed-lettuce mixtures. Smooth pigweed was not responsive to P rates. However, luxurious P consumption by smooth pigweed occurred, reducing the amount of the nutrient available for lettuce absorption. In common purslane-lettuce mixtures, the weed was responsive to P rates, increasing its competitive ability, whereas no increase in lettuce competitive ability was observed. Both weed species were more competitive than lettuce. Competition for P appears to be the main mechanism of common purslane interference on lettuce grown in low-P organic soils. Alternative fertilization strategies (i.e., banded applications) may reduce the effect of smooth pigweed on lettuce.
8
Hagood, Edward S. "Control of Triazine-Resistant Smooth Pigweed (Amaranthus hybridus) and Common Lambsquarters (Chenopodium album) in No-till Corn (Zea mays)." Weed Technology 3, no. 1 (1989): 136–42. http://dx.doi.org/10.1017/s0890037x00031481.
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Field experiments were established to evaluate preemergence and postemergence herbicides for control of triazine-resistant smooth pigweed and common lambsquarters in no-till corn. When applied preemergence, alachlor in the microencapsulated formulation controlled smooth pigweed better than the emulsifiable concentrate formulation and better than either metolachlor or pendimethalin. These herbicides applied preemergence did not control common lambsquarters consistently. Pendimethalin controlled both triazine-resistant species when applied as a sequential treatment of a preemergence and an early postemergence application. Control of triazine-resistant smooth pigweed and common lambsquarters was excellent when dicamba was applied early postemergence in treatments containing alachlor, metolachlor, or pendimethalin applied preemergence and/or early postemergence. Thiameturon and CGA-131036 controlled triazine-resistant smooth pigweed with acceptable crop tolerance. Thiameturon also controlled common lambsquarters, but control was unacceptable with CGA-131036.
9
Gossett, Billy J., and Joe E. Toler. "Differential Control of Palmer Amaranth (Amaranthus palmeri) and Smooth Pigweed (Amaranthus hybridus) by Postemergence Herbicides in Soybean (Glycine max)." Weed Technology 13, no. 1 (1999): 165–68. http://dx.doi.org/10.1017/s0890037x00045085.
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Field studies were conducted in South Carolina to evaluate the herbicides acifluorfen, chlorimuron, and imazaquin for control of Palmer amaranth and smooth pigweed in soybean, when applied 3 wk after weed emergence. Palmer amaranth was more difficult to control than smooth pigweed. Compared to untreated controls, acifluorfen, chlorimuron, and imazaquin reduced Palmer amaranth and smooth pigweed biomass 78 and 96%, 80 and 98%, and 82 and 99% at 30 d after treatment (DAT), 60 DAT, and at soybean harvest, respectively. The high rate (140 g/ha) of imazaquin provided greater control of Palmer amaranth than other herbicide treatments at soybean harvest. Except for the 140 g/ha rate of imazaquin, inadequate control of Palmer amaranth resulted in lower soybean seed yields for all herbicide treatments than the weed-free control. However, all herbicides controlled smooth pigweed to provide soybean seed yields similar to the weed-free control.
10
Ritter, Ronald L., Thomas C. Harris, and William J. Varano. "Influence of Herbicides and Tillage on the Control of Triazine-Resistant Smooth Pigweed (Amaranthus hybridus) in Corn (Zea mays) and Soybeans (Glycine max)." Weed Science 33, no. 3 (1985): 400–404. http://dx.doi.org/10.1017/s0043174500082503.
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In field studies, a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] followed by an early postemergence application of dicamba (3,6-dichloro-o-anisic acid) gave good season-long control of smooth pigweed (Amaranthus hybridusL. ♯ AMACH) in conventional and no-till corn (Zea maysL. ‘Pioneer 3184’ and ‘Pioneer 3382’). In soybeans [Glycine max(L.) Merr. ‘Williams' and ‘Essex’], best control of smooth pigweed was achieved with an early postemergence application of sethoxydim {2-[1-(ethyoxy-imino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} plus acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Tillage played a role in the degree of smooth pigweed control. Best control of smooth pigweed in corn was obtained when the ground was moldboard plowed and disced, and least control was obtained when corn was no-till planted in the previous year's corn stalks or in a rye (Secale cerealeL.) cover crop.
11
Steckel, Lawrence E., Christy L. Sprague, Edward W. Stoller, and Loyd M. Wax. "Temperature effects on germination of nineAmaranthusspecies." Weed Science 52, no. 2 (2004): 217–21. http://dx.doi.org/10.1614/ws-03-012r.
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Germination of weed seed and time of emergence are greatly affected by temperature. The effects of temperature on seed germination of tumble pigweed, prostrate pigweed, smooth pigweed, Palmer amaranth, Powell amaranth, spiny amaranth, redroot pigweed, common waterhemp, and tall waterhemp were examined under constant and alternating temperature regimens at 5, 10, 15, 20, 25, 30, and 35 C. Averaged over all temperatures, alternating temperature regimens increased total germination of all species, except Powell amaranth, which germinated similarly under both constant and alternating temperatures. In addition, Powell amaranth seed exhibited the highest total germination across all temperatures compared with the other amaranth species. Prostrate pigweed seed demonstrated the lowest total germination. Optimal temperatures for maximum germination were greater than 20 C for all species, except prostrate pigweed. The alternating temperature regimen centering at 30 C was used to compare the germination rates of the nine species. Palmer amaranth and smooth pigweed attained complete germination on the first day. The rate of germination for these species was much more rapid than the otherAmaranthusspp., which took 3 to 8 d to reach 50% germination.
12
Santos, Bielinski M., Joan A. Dusky, William M. Stall, Thomas A. Bewick, and Donn G. Shilling. "Mechanisms of interference of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) on lettuce as influenced by phosphorus fertility." Weed Science 52, no. 1 (2004): 78–82. http://dx.doi.org/10.1614/p2002-171.
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Greenhouse studies were conducted to assess the intensity of smooth pigweed and common purslane aboveground interference (AI) and belowground interference (BI) with lettuce and to determine primary mechanisms of interference of each species as affected by P fertility rates. Lettuce was transplanted in mixtures with either smooth pigweed or common purslane according to four partitioning regimes: no interference, full interference, BI, and AI. Soil used was low in P for optimum lettuce yields, therefore P was added at rates of 0, 0.4, and 0.8 grams of P per liter of soil. Shoot and root biomass and plant height were measured for each species, as well as P tissue content. The data obtained indicated that smooth pigweed interfered with lettuce primarily through light interception by its taller canopy. A secondary mechanism of interference was the absorption of P from the soil through luxury consumption, increasing the P tissue content without enhancing smooth pigweed biomass accumulation. In contrast, common purslane competed aggressively with lettuce for P. Because the weed grew taller than lettuce, light interception was a secondary interference factor.
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Manley, Brian S., Kriton K. Hatzios, and Henry P. Wilson. "Absorption, Translocation, and Metabolism of Chlorimuron and Nicosulfuron in Imidazolinone-Resistant and -Susceptible Smooth Pigweed (Amaranthus hybridus)." Weed Technology 13, no. 4 (1999): 759–64. http://dx.doi.org/10.1017/s0890037x00042196.
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The absorption, translocation, and metabolism of the ethyl ester of chlorimuron and nicosulfuron in resistant (R) and susceptible (S) smooth pigweed (Amaranthus hybridus) were investigated. R and S smooth pigweed seedlings (5 to 10 cm tall) were treated with foliar-applied14C-labeled chlorimuron and nicosulfuron and harvested at 3, 6, 24, and 72 h after application. Chlorimuron absorption increased with time in both populations of smooth pigweed and was higher in the R accession only at 6 h after application. Nicosulfuron absorption did not increase with time in the R accession, and after 6 h, there were no differences between the R and S accessions. Absorbed chlorimuron and nicosulfuron were translocated to shoots and leaves above and below the treated leaf, but not into the roots in both accessions. Translocation of chlorimuron and nicosulfuron out of the treated leaf was also similar in the two accessions. Metabolism of14C-chlorimuron occurred more rapidly in the R accession with approximately 68% remaining as chlorimuron at 3 h after application. At the same time period, 81% of the absorbed radioactivity remained as chlorimuron in the S accession. Metabolism of14C-chlorimuron at 24 and 72 h after application was greater in the S than the R accession of smooth pigweed. Metabolism of14C-nicosulfuron was similar in the two accessions and did not increase with time. Rapid herbicide metabolism may explain the twofold level of crossresistance of the R accession of smooth pigweed to chlorimuron at the whole plant level.
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Manley, Brian S., Henry P. Wilson, and Thomas E. Hines. "Characterization of Imidazolinone-Resistant Smooth Pigweed (Amaranthus hybridus)." Weed Technology 12, no. 4 (1998): 575–84. http://dx.doi.org/10.1017/s0890037x00044407.
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Following six consecutive annual applications of imazaquin in combination with trifluralin or pendimethalin to several soybean fields on the Delmarva Peninsula, unacceptable smooth pigweed control was observed. Field and greenhouse studies were conducted to determine if this population of smooth pigweed was resistant to imazaquin and other herbicides. In field research, imazaquin and imazethapyr gave complete control of the susceptible (S) population while providing no control of the resistant (R) population; pyrithiobac controlled 99 and 90% of the R and S populations, respectively. Pendimethalin, metribuzin, MON-12000, and flumiclorac gave less than 75% control of both S and R populations. Chlorimuron, primisulfuron, CGA-152005, and lactofen gave above 75% control, and thifensulfuron and nicosulfuron gave above 90% control of both S and R populations. Seeds were collected from the R and S smooth pigweed populations for research in the greenhouse. Greenhouse studies confirmed high levels of resistance to imazaquin and imazethapyr and low levels of cross-resistance to rimsulfuron and chlorimuron in the R population. Susceptibility of the R population to nicosulfuron, thifensulfuron, pyrithiobac, and pendimethalin was comparable to that of the S population.
15
Coffman, C. Benjamin, and J. Ray Frank. "Weed-Crop Responses to Weed Management Systems in Conservation Tillage Corn (Zea mays)." Weed Technology 5, no. 1 (1991): 76–81. http://dx.doi.org/10.1017/s0890037x00033297.
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Continuous corn was grown for 5 consecutive yr using conservation tillage methods in the Maryland Piedmont. Herbicide treatments were applied annually at common usage rates and were compared for their effects on weed cover, species stability, and grain production. Weed flora dominance shifted from giant foxtail the first year to smooth pigweed the following year. Smooth pigweed then dominated the flora for the duration of the study. Horsenettle was ubiquitous in all treatments but never became competitive. Canada thistle occurred in measurable densities in all plots that had not received atrazine applied preemergence. Grain yields were correlated negatively with densities of smooth pigweed in 1983 (r = −0.58, P = 0.01), and Canada thistle in 1983 and 1984 (r = −0.63 and −0.62, respectively; P = 0.05). Grain yields were correlated positively with midseason precipitation (r = 0.85, P = 0.01).
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Majek, Bradley A., Philip E. Neary, and Dean F. Polk. "Smooth Pigweed Interference in Newly Planted Peach Trees." Journal of Production Agriculture 6, no. 2 (1993): 244–46. http://dx.doi.org/10.2134/jpa1993.0244.
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Collins, Amanda S., Carlene A. Chase, William M. Stall, and Chad M. Hutchinson. "Competitiveness of Three Leguminous Cover Crops with Yellow Nutsedge (Cyperus esculentus) and Smooth Pigweed (Amaranthus hybridus)." Weed Science 55, no. 6 (2007): 613–18. http://dx.doi.org/10.1614/ws-07-044.1.
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Greenhouse replacement-series experiments were conducted to evaluate the competitiveness of cowpea, sunn hemp, and velvetbean when grown in combination with yellow nutsedge and smooth pigweed. The effect of the cover crop species on yellow nutsedge tuber production was also evaluated. Cowpea and velvetbean were equally competitive with yellow nutsedge, but sunn hemp was less competitive. Although sunn hemp height was double that of cowpea or velvetbean, photosynthetically active radiation penetrating to the soil surface was twofold to eightfold greater than with the other two species. Leaf area per plant with sunn hemp monocultures were only 63 to 70% of cowpea and 37 to 41% of velvetbean. Increasing the proportion of cover crops in crop : weed mixtures did not significantly affect nutsedge tuber number per plant or tuber weight per plant. Cowpea was more competitive than smooth pigweed, whereas both sunn hemp and velvetbean were less competitive than smooth pigweed. The utility and efficacy of leguminous cover crop species for nutsedge and smooth pigweed suppression do not appear to be due to inherent competitiveness. Until cultivars that are more competitive become available, cultural measures should be employed that enhance cover crop modification of soil environmental conditions to minimize weed seed germination and vegetative propagule sprouting.
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Whaley, Cory M., Henry P. Wilson, and James H. Westwood. "ALS resistance in several smooth pigweed (Amaranthus hybridus) biotypes." Weed Science 54, no. 5 (2006): 828–32. http://dx.doi.org/10.1614/ws-05-040r.1.
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Experiments were conducted to identify acetolactate synthase (ALS, EC 2.2.1.6 [formerly EC 4.1.3.18]) mutation sites in eight biotypes of smooth pigweed and correlate these mutations with patterns of herbicide cross-resistance. Four herbicide-resistant smooth pigweed biotypes (R5, R6, R7, R8) collected from fields in Virginia, Delaware, and Maryland, showed a similar response to postemergence applications of the ALS-inhibitors imazethapyr, pyrithiobac, chlorimuron, thifensulfuron, and cloransulam. These R biotypes ranged from 261- to 537-fold resistant to imazethapyr and 29- to 88-fold resistant to pyrithiobac. The biotypes also had reduced sensitivity to chlorimuron and thifensulfuron of 2- to 14-fold and 10- to 25-fold, respectively, relative to a susceptible smooth pigweed biotype (S). Biotypes R6, R7, and R8 had reduced sensitivity of 3- to 10-fold to cloransulam relative to the S biotype, whereas R5 had increased sensitivity. All of these biotypes were found to have a serine to asparagine substitution at amino acid position 653, as numbered relative to the protein sequence ofArabidopsis thaliana. This stands in contrast to four other imidazolinone (IMI)-resistant smooth pigweed biotypes (R1, R2, R3, R4) that were collected from fields in Somerset County, Maryland. These biotypes were found to have an alanine to threonine substitution at position 122 of the ALS enzyme and were previously characterized at the whole-plant level with high-level resistance to IMI herbicides, increased sensitivity to pyrimidinylthiobenzoate and triazolopyrimidine sulfonanilide herbicides, and low to no cross-resistance to sulfonylurea herbicides.
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Foy, Chester L., and Harold L. Witt. "SAN 582, Alachlor, and Metolachlor Control Triazine-Resistant (TR) Smooth Pigweed (Amaranthus hybridus) in No-Till Corn (Zea mays)." Weed Technology 11, no. 3 (1997): 623–25. http://dx.doi.org/10.1017/s0890037x0004553x.
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SAN 582 at 1.1, 1.2, 1.3, 1.5, and 1.6 kg ai/ha; alachlor at 1.7, 2.2, and 2.8 kg/ha; and metolachlor at 1.7, 2.2, and 2.8 kg/ha were applied preemergence without and with atrazine at 1.7 kg/ha in no-till corn at two locations near Blacksburg, VA, in 1993 and 1994. SAN 582, alachlor, and metolachlor controlled TR-smooth pigweed when applied without or with atrazine, and with only a few exceptions, control was greater than 60%. The highest rate of individual herbicides was more effective than the lowest rate in most cases. Early control of TR-smooth pigweed was similar from all three herbicides, especially at higher rates, but control later in the season tended to be best with alachlor. As expected, atrazine applied alone did not control TR-smooth pigweed, and crop yields were increased with herbicide treatments compared to no treatment.
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Teasdale, John R., Parthan Pillai, and Ronald T. Collins. "Synergism between cover crop residue and herbicide activity on emergence and early growth of weeds." Weed Science 53, no. 4 (2005): 521–27. http://dx.doi.org/10.1614/ws-04-212r.
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Cover crop residues and other biologically based approaches often provide incomplete and inconsistent weed control. This research was conducted to evaluate interactions between hairy vetch residue on the surface of soil and the herbicide metolachlor. Herbicide was applied and incorporated with simulated rainfall before residue placement, residue was applied to the soil surface at precise rates, and potentially confounding variables such as nitrogen and soil moisture were controlled in a greenhouse experiment. Emphasis was placed on the use of suboptimal rates of both residue and metolachlor to explore the potential synergistic interactions between these factors. Deviation from a multiplicative model that included a quadratic response to hairy vetch residue and a log-logistic response to metolachlor was used to demonstrate the presence or absence of synergism. This model effectively showed that emergence of smooth pigweed, common lambsquarters, giant foxtail, and velvetleaf and early growth of smooth pigweed and common lambsquarters were reduced synergistically by the combination of hairy vetch residue and metolachlor. For example, smooth pigweed emergence was reduced 13% by 500 g m−2of hairy vetch residue alone and was reduced 16% by 10 g ha−1of metolachlor alone, but together, they reduced smooth pigweed emergence by 86%. This model could be used to determine synergistic interactions between any combination of a phytotoxin and a biologically based weed management approach that could be expressed in quantitative units.
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Ahrens, William H. "Uptake and Action of Metribuzin in Soybeans (Glycine max) and Two Weed Species as Monitored by Chlorophyll Fluorescence." Weed Science 37, no. 5 (1989): 631–38. http://dx.doi.org/10.1017/s0043174500072556.
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Terminal fluorescence (FT) was monitored following root or foliar uptake of metribuzin in soybean, velvetleaf, and smooth pigweed seedlings grown in solution culture. These species are known to be tolerant, moderately susceptible, and susceptible, respectively, to metribuzin under field conditions. The indirect monitoring of herbicide metabolism by fluorescence is complicated by several factors (particularly photoinhibition) and is difficult to interpret when plants are kept in the light. Rapid declines in FTat metribuzin concentrations causing high photosystem II reaction center inhibition were interpreted, in conjunction with fresh weight and injury data, as resulting from photoinhibition in velvetleaf and smooth pigweed, and from a combination of photoinhibition and herbicide metabolism in soybeans. At lower concentrations, FTdeclines were apparently not affected by photoinhibition but were probably representative of herbicide metabolism. These results suggested a significant rate of metribuzin metabolism in soybeans, a minor degree of metabolism in smooth pigweed beginning after 12 h, and no detectable metabolism in velvetleaf. FTmonitored over a 24-h dark period following foliar absorption showed declines in soybeans indicating a modest degree of metribuzin metabolism (at intermediate herbicide doses) but no FTdeclines attributable to herbicide metabolism in velvetleaf or smooth pigweed. Results indicate that the inhibition of a high percentage of photosystem II reaction centers is required before photoinhibition and photooxidative leaf damage can result from photosystem II inhibitor herbicides such as metribuzin.
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Vencill, William K., and Chester L. Foy. "Distribution of Triazine-Resistant Smooth Pigweed (Amaranthus hybridus) and Common Lambsquarters (Chenopodium album) in Virginia." Weed Science 36, no. 4 (1988): 497–99. http://dx.doi.org/10.1017/s0043174500075251.
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The distribution pattern ofs-triazine-resistant biotypes of common lambsquarters (Chenopodium albumL. #3CHEAL) and smooth pigweed (Amaranthus hybridusL. # AMACH) in Virginia was determined. Seeds were collected from suspected triazine-resistant biotypes of both species. Triazine resistance was confirmed by measuring chlorophyll fluorescence in the presence of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine]. Greenhouse bioassay with whole-plant material and a sinking leaf disc assay were also performed as further confirmation of triazine resistance. Triazine-resistant smooth pigweed was confirmed in 19 counties and common lambsquarters in eight counties in Virginia. Triazine-resistant smooth pigweed and common lambsquarters were located mostly in the northern and southwestern highlands of the state where there has been a long history of triazine use in no-till corn (Zea maysL.) production.S-triazine-resistant biotypes were also cross-resistant to other representatives-triazine andas-triazine herbicides but susceptible to the substituted urea herbicide diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].
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Santos, Bielinski M., Joan A. Dusky, William M. Stall, Donn G. Shilling, and Thomas A. Bewick. "Influence of Smooth Pigweed (Amaranthus hybridus) and Common Purslane (Portulaca oleracea) Densities on Lettuce Yields under Different Phosphorus Fertility Regimes." HortScience 32, no. 3 (1997): 431A—431. http://dx.doi.org/10.21273/hortsci.32.3.431a.
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The effects of different populations densities of smooth pigweed and common purslane were determined in field trials conducted in organic soils. `South Bay' lettuce was planted in twin rows on 90-cm planting beds. Weed densities used were 0, 2, 4, 8, and 16 weeds per 6 m of row (5.4 m2). Phosphorus (P) was applied broadcast (1200 kg P/ha) and banded 2 inches below each lettuce row (600 kg P/ha). Lettuce fresh weights were collected 8 weeks after emergence. Data collected indicated that P regime and density had significant effects on lettuce yield and quality. For both weeds, yield decreased as density increased. In all cases, lettuce showed greater yields at a given density when grown with P banded than when P was applied broadcast. Critical density for smooth pigweed for P broadcast was between 2 and 4 plants per 5.4 m2, whereas this critical density occurred between 8 and 16 plants per 5.4 m2 when P was banded. Yield reductions of up to 24.4% and 20.1% occurred at the highest smooth pigweed density for broadcast and banded P, respectively. Two common purslane plants per 5.4 m2 were enough to reduce lettuce yields. Banding P helped lettuce to produce significantly more within each common purslane density. Yield reductions of 47.8% and 44.3% occurred at the highest common purslane density for broadcast and banded P, respectively. Apparently, banding P gives an additional advantage to the crop against smooth pigweed and common purslane.
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Santos, Bielinski M., Joan A. Dusky, William M. Stall, Donn G. Shilling, and Thomas A. Bewick. "Effects of Phosphorus Fertility Regimes and Smooth Pigweed (Amaranthus hybridus) and Common Purslane (Portulaca oleracea) Removal Times on Lettuce Yields." HortScience 32, no. 3 (1997): 431B—431. http://dx.doi.org/10.21273/hortsci.32.3.431b.
Full textAbstract:
The effects of different smooth pigweed and common purslane removal times and two phosphorus (P) fertility regimes were studied under field conditions. Head lettuce (cv. South Bay) in organic soils low in P fertility. Smooth pigweed and common purslane were grown at a density of 16 plants per 6 m of row (5.4 m2) and five removal times (0, 2, 4, 6, and 8 weeks) after lettuce emergence. Phosphorus (P) was applied broadcast (1200 kg P/ha) and banded 2 inches below each lettuce row (600 kg P/ha). Lettuce fresh weights were collected 8 weeks after emergence. When smooth pigweed was removed after 4 weeks, significant reductions (–17%) were observed for P banding. However, these reductions occurred after 2 weeks if P was broadcast. No significant differences were observed if removal was imposed later for P broadcast, whereas lettuce yields gradually decreased as removal time was delayed. These findings indicate that P banding can counteract the negative impact of smooth pigweed on lettuce and may allow farmers to delay weed control (if necessary) for another 2 weeks without significant yield reductions. Common purslane interference did not cause significant lettuce yield reductions as compared to the weed-free control for 6 weeks when P was banded, whereas this was true for P broadcast up to 4 weeks. Phosphorus fertility regime significantly influenced the period of weed interference of common purslane with lettuce, reducing its impact when P was banded.
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Street, Joe E., Charles E. Snipes, John A. McGuire, and Gale A. Buchanan. "Competition of a Binary Weed System with Cotton (Gossypium hirsutum)." Weed Science 33, no. 6 (1985): 807–9. http://dx.doi.org/10.1017/s0043174500083399.
Full textAbstract:
Cotton (Gossypium hirsutumL. ‘Stoneville 213’) was grown on Lucedale fine sandy loam with sicklepod (Cassia obtusifoliaL. ♯ CASOB) and a complex of redroot pigweed (Amaranthus retroflexusL. ♯ AMARE) and smooth pigweed (A. hybridusL. ♯ AMACH) in all possible combinations of 0, 1, 2, 4, 8, and 16 weeds of each species per 7.5 m of row. Seed cotton yields decreased as a quadratic function of increasing weed density. One pigweed and one sicklepod plant per 7.5 m of row reduced yields by 9 and 9.7% in 1979 and 1980, respectively. At low levels of infestation (≤4 weeds/7.5 m of row), the competitive effect of pigweed and sicklepod was additive; however, at the high densities, the competitive effect was not additive. Mechanical harvesting efficiency and cotton maturity were not decreased by any weed density. Sicklepod was more competitive than pigweed in both years.
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Black, B. David, James L. Griffin, John S. Russin, and Johnnie P. Snow. "Weed Hosts forRhizoctonia solani, Causal Agent for Rhizoctonia Foliar Blight of Soybean (Glycine max)." Weed Technology 10, no. 4 (1996): 865–69. http://dx.doi.org/10.1017/s0890037x00040938.
Full textAbstract:
Greenhouse studies were conducted to determine host status of weed species forRhizoctonia solaniAG-1, which causes Rhizoctonia foliar blight of soybean. Weed species were barnyardgrass, broadleaf signalgrass, common cocklebur, entireleaf morningglory, hemp sesbania, itchgrass, johnsongrass, large crabgrass, northern jointvetch, prickly sida, purple nutsedge, redweed, sicklepod, and smooth pigweed. Seedling weeds were inoculated with suspensions containing intraspecific group IA and IB isolates of the fungus. In the first study, sclerotia of IA were recovered from tissue of all weeds except smooth pigweed, and mycelia of IA were recovered from all except smooth pigweed and redweed. In that study, neither microsclerotia nor mycelia of IB were recovered from sicklepod, barnyardgrass, or large crabgrass, and only microsclerotia were recovered from itchgrass and purple nutsedge. In the second study, sclerotia of IA, microsclerotia of IB, and mycelia of each isolate were recovered from all weed species. In other studies,R. solanispread from at least six of seven weed species to a noninfected soybean plant growing in close proximity. These studies emphasize the importance of weed control, not only for reducing plant competition and increasing yield, but also for the potential impact on development of RFB.
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Poston, Daniel H., Jingrui Wu, Kriton K. Hatzios, and Henry P. Wilson. "Enhanced sensitivity to cloransulam-methyl in imidazolinone-resistant smooth pigweed." Weed Science 49, no. 6 (2001): 711–16. http://dx.doi.org/10.1614/0043-1745(2001)049[0711:estcmi]2.0.co;2.
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Trucco, Federico, Tatiana Tatum, Kenneth R. Robertson, A. Lane Rayburn, and Patrick J. Tranel. "Characterization of Waterhemp (Amaranthus tuberculatus) × Smooth Pigweed (A. hybridus) F1Hybrids." Weed Technology 20, no. 1 (2006): 14–22. http://dx.doi.org/10.1614/wt-05-018r.1.
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In the state of Illinois, waterhemp and smooth pigweed are among the worst agricultural weeds. Previous research shows high potential for hybridization between these two species. However, the actual occurrence of hybrids in natural settings is still uncertain. Morphological similarity between hybrids and waterhemp makes field surveys of hybrids difficult to conduct. The main purpose of this study was to characterize the morphology of waterhemp × smooth pigweed F1hybrids, emphasizing evaluation of characters that may allow for hybrid discrimination in fieldAmaranthuscommunities. Concurrently, the study characterized hybrid reproductive fitness, chromosome number, and DNA content. To accomplish this, hybrids were obtained from field crosses. A species-specific polymorphism in theALSgene was used to verify hybrid identity. Significant differences (α = 0.05) between hybrids and individuals of the parental species were observed for five staminate and five carpellate characters. Of these, five characters differentiated hybrids from waterhemp. However, clustering analyses using these characters indicated that morphological differences were not reliable enough, by themselves, for unambiguous hybrid identification. Also, hybrid homoploidy (2n= 32) with respect to parental species excluded chromosome counts in hybridity determinations. However, DNA content analysis may be used for such purpose. Hybrids had an average of 1.21 pg of DNA per 2C nucleus, a value intermediate to that of parental species. Hybrids produced 3.3 or 0.7% the seed output of parental and sibling waterhemp individuals, respectively. Percent micropollen in hybrids was 95-times greater than in parental species. Hybrid sterility appears to be the most reliable feature for hybrid discrimination when conducting field surveys. However, molecular and cytogenetic analyses as employed in this study may be desired for ultimate identity corroboration.
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Teasdale, John R., and Steven B. Mirsky. "Tillage and Planting Date Effects on Weed Dormancy, Emergence, and Early Growth in Organic Corn." Weed Science 63, no. 2 (2015): 477–90. http://dx.doi.org/10.1614/ws-d-14-00112.1.
Full textAbstract:
Insufficient weed control is a major constraint to adoption of reduced-tillage practices for organic grain production. Tillage, cover crop management, and crop planting date are factors that influence emergence periodicity and growth potential of important weed species in these systems. We assessed two hairy vetch cover crop management practices, disk-kill and roll-kill, across a range of corn planting dates from early May to late June in three experiments in Beltsville, MD. Patterns of seed dormancy, emergence, and early weed growth were determined for overseeded populations of common ragweed, giant foxtail, and smooth pigweed, three important species in the Mid-Atlantic states that represent early to late emergence. Common ragweed emergence was lowest and dormancy was highest of the three species across all planting dates. Giant foxtail emergence was higher than the other species in roll-killed hairy vetch and included a significant number of seeds that germinated before rolling operations in late June. Smooth pigweed had the highest emergence and lowest dormancy in disk-killed hairy vetch in June. Individual giant foxtail plant weight was higher in roll-killed than disk-killed hairy vetch in 2 of 3 yr, whereas that of smooth pigweed plants was higher in disk-killed than roll-killed vetch in 2 of 3 yr. Giant foxtail was the dominant species in roll-killed hairy vetch (averaged 79% of total weed biomass at corn silking), probably because of early germination and establishment before rolling operations. Smooth pigweed was the dominant species in disk-killed hairy vetch at June planting dates (averaged 77% of total weed biomass), probably because of high growth rates under warm conditions in tilled soil. This research demonstrated that cover crop management practices and the timing of planting operations can shift the dominant species of weed communities in organic farming systems and must be considered in long-term weed management planning.
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Thomas, Walter E., Tim T. Britton, Scott B. Clewis, Shawn D. Askew, and John W. Wilcut. "Glyphosate-Resistant Cotton (Gossypium hirsutum) Response and Weed Management with Trifloxysulfuron, Glyphosate, Prometryn, and MSMA." Weed Technology 20, no. 1 (2006): 6–13. http://dx.doi.org/10.1614/wt-04-257r1.1.
Full textAbstract:
Field studies were conducted at three locations to evaluate glyphosate-resistant (GR) cotton response, weed control, and cotton lint yields to two formulations of glyphosate (diammonium salt– glyphosate and isopropylamine salt–glyphosate) and trifloxysulfuron applied early postemergence (EPOST) alone or to tank mixtures of trifloxysulfuron with each glyphosate formulation, with and without a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA. Trifloxysulfuron and both formulations of glyphosate controlled common lambsquarters and pitted morningglory. Both glyphosate formulations provided equivalent control of common lambsquarters, goosegrass, pitted morningglory, prickly sida, and smooth pigweed. Trifloxysulfuron controlled smooth pigweed better than either glyphosate formulation but did not control goosegrass or prickly sida. Prometryn plus MSMA LAYBY improved late-season control of common lambsquarters, goosegrass, large crabgrass, and pitted morningglory for all EPOST systems and improved late-season smooth pigweed control for EPOST systems that did not include trifloxysulfuron. Cotton injury was 2% or less from both glyphosate formulations, while trifloxysulfuron injured ‘Deltapine 5415RR’ 7 to 16% at two locations. At a third location, trifloxysulfuron injured ‘Paymaster 1218RR/BG’ 24%, and when applied in mixture with either glyphosate formulation, injury increased to at least 72%. Cotton injury was transient at the first two locations and was not visually apparent 3 to 5 wk later. Cotton yield at the third location was reduced. High cotton yields reflected high levels of weed control.
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Ullrich, Silke D., Jeffrey S. Buyer, Michel A. Cavigelli, Rita Seidel, and John R. Teasdale. "Weed Seed Persistence and Microbial Abundance in Long-Term Organic and Conventional Cropping Systems." Weed Science 59, no. 2 (2011): 202–9. http://dx.doi.org/10.1614/ws-d-10-00142.1.
Full textAbstract:
Weed seed persistence in soil can be influenced by many factors, including crop management. This research was conducted to determine whether organic management systems with higher organic amendments and soil microbial biomass could reduce weed seed persistence compared with conventional management systems. Seeds of smooth pigweed and common lambsquarters were buried in mesh bags in organic and conventional systems of two long-term experiments, the Farming Systems Project at the Beltsville Agricultural Research Center, Maryland, and the Farming Systems Trial at the Rodale Institute, Pennsylvania. Seed viability was determined after retrieval at half-year intervals for 2 yr. Total soil microbial biomass, as measured by phospholipid fatty acid (PLFA) content, was higher in organic systems than in conventional systems at both locations. Over all systems, locations, and experiments, viable seed half-life was relatively consistent with a mean of 1.3 and 1.1 yr and a standard deviation of 0.5 and 0.3 for smooth pigweed and common lambsquarters, respectively. Differences between systems were small and relatively inconsistent. Half-life of smooth pigweed seeds was shorter in the organic than in the conventional system in two of four location-experiments. Half-life of common lambsquarters was shorter in the organic than in the conventional system in one of four location-experiments, but longer in the organic than in the conventional system in two of four location-experiments. There were few correlations between PLFA biomarkers and seed half-lives in three of four location-experiments; however, there were negative correlations up to −0.64 for common lambsquarters and −0.55 for smooth pigweed in the second Rodale experiment. The lack of consistent system effects on seed persistence and the lack of consistent associations between soil microbial biomass and weed seed persistence suggest that soil microorganisms do not have a dominating role in seed mortality. More precise research targeted to identifying specific microbial functions causing seed mortality will be needed to provide a clearer picture of the role of soil microbes in weed seed persistence.
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Hohlt, H. E., H. P. Wilson, and T. E. Hines. "THE USE OF LOW RATES OF CLOMAZONE ON WATERMELON." HortScience 25, no. 8 (1990): 857a—857. http://dx.doi.org/10.21273/hortsci.25.8.857a.
Full textAbstract:
During 1989, clomazone (Command) was applied pretransplant or preemergence to transplanted and seeded watermelon (Citrullus lanatus, cv. Charleston Gray), respectively. Rates of 280, 414, and 560 g ai·ha-1 (0.50, 0.75, 1.0 pt/A) clomazone were applied to a Bojac sandy loam. Plots were rated for percentage weed control 21 DAT. Control of common lambsquarters [Chenopodium album (L.)], large crabgrass [Digitaria sanguinalis (L.) Scop.], and smooth pigweed (Amaranthus hybridus L.) increased with rate although smooth pigweed control was low. A significant phytotoxic injury characterized by bleaching and reduced growth occurred at all rates on melon transplants. No significant phytotoxicity occurred in seeded plots 35 DAT. Vine length (cm) was recorded 42 DAT. Vine length was reduced significantly at the 560 g·ha-1 rate in transplants. Vine length of seeded watermelons was not significantly affected.
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Poston, Daniel H., Henry P. Wilson, and Thomas E. Hines. "Growth and development of imidazolinone-resistant and -susceptible smooth pigweed biotypes." Weed Science 50, no. 4 (2002): 485–93. http://dx.doi.org/10.1614/0043-1745(2002)050[0485:gadoir]2.0.co;2.
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Reddy, Krishna N., Martin A. Locke, and Kevin D. Howard. "Bentazon Spray Retention, Activity, and Foliar Washoff in Weed Species." Weed Technology 9, no. 4 (1995): 773–78. http://dx.doi.org/10.1017/s0890037x00024192.
Full textAbstract:
Greenhouse studies were conducted to investigate the effects of adjuvant and rainfall on bentazon spray retention, efficacy, and foliar washoff in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Bentazon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil concentrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blend (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk after treatment was similar with either adjuvant on velvetleaf and smooth pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklepod as compared to COC. Rainfall at 1 h after application generally reduced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application as compared to COC. Overall, bentazon spray retention on plants was 9 to 550% higher with OSB as compared to COC among the species at 1 h after application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adjuvants except in smooth pigweed and ranged from 39 to 98% among the four weed species at 1 h after application. OSB exhibited specificity for certain weed species and the potential to minimize bentazon spray reaching the soil by increasing deposition.
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Liebl, Rex A., and Michael A. Norman. "Mechanism of Clomazone Selectivity in Corn (Zea mays), Soybean (Glycine max), Smooth Pigweed (Amaranthus hybridus), and Velvetleaf (Abutilon theophrasti)." Weed Science 39, no. 3 (1991): 329–32. http://dx.doi.org/10.1017/s004317450007301x.
Full textAbstract:
Based on chlorophyll content, hydroponically cultured soybean seedlings were 254, 66, and 13 times more tolerant to clomazone than velvetleaf, corn, and smooth pigweed, respectively. Clomazone, at concentrations that inhibited chlorophyll, did not affect fresh weight accumulations of any species except velvetleaf. However, in velvetleaf, fresh weight accumulation was only half as sensitive to clomazone as the leaf chlorophyll content. Uptake of14C-clomazone from nutrient solution by 72 h after treatment (HAT) (pigweed > velvetleaf > soybean > corn) indicates that differential absorption cannot account for selectivity. Shoot:root ratios of14C recovered from soybean, corn, velvetleaf, and pigweed by 72 HAT were 0.39, 0.84, 1.67, and 2.37, respectively. The limited acropetal clomazone translocation in soybean seedlings may account to a small degree for soybean tolerance to clomazone. Conversion of clomazone to more polar metabolites was rapid in all four species. There were no significant differences among species in the percentage of14C activity recovered as clomazone from root tissue by 72 HAT. Of the14C activity recovered from shoots of soybean, corn, pigweed, and velvetleaf seedlings by 72 HAT, 46, 59, 35, and 54%, respectively, was clomazone. Differences in clomazone uptake, distribution, and metabolism among the four species were either insignificant or poorly correlated to selectivity, and therefore cannot account for the tremendous differences in clomazone sensitivity among these species. These observations indicate, indirectly, that differences at the site of action may account for selectivity.
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Jordan, David L., Alan C. York, Marilyn R. McClelland, and Robert E. Frans. "Clomazone as a Component in Cotton (Gossypium hirsutum) Herbicide Programs." Weed Technology 7, no. 1 (1993): 202–11. http://dx.doi.org/10.1017/s0890037x00037131.
Full textAbstract:
Efficacy of herbicide programs containing clomazone PPI plus fluometuron PRE or clomazone plus pendimethalin PPI plus fluometuron PRE was compared with that of standard programs of pendimethalin PPI plus fluometuron PRE and norflurazon PPI plus norflurazon and fluometuron PRE. Cotton injury was less than 5% with all treatments when disulfoton or phorate was applied in the seed furrow. Control of fall panicum, goosegrass, large crabgrass, eclipta, entireleaf morningglory, ivyleaf morningglory, pitted morningglory, tall morningglory, prickly sida, redroot pigweed, smooth pigweed, hemp sesbania, spotted spurge, sicklepod, and velvetleaf and cotton yields with 0.8 kg ai ha−1 of clomazone plus fluometuron or 0.6 kg ha−1 of clomazone plus pendimethalin plus fluometuron equalled or exceeded that from the standard herbicide programs. POST-directed application of methazole at 0.8 kg ai ha−1 plus MSMA at 2.2 kg ae ha−1 increased sicklepod and morningglory control and cotton yield. Clomazone applied PRE at 0.6 kg ha−1 with fluometuron controlled broadleaf signalgrass, goosegrass, large crabgrass, prickly sida, and smooth pigweed equally with that of standard treatments of trifluralin or trifluralin plus norflurazon PPI and fluometuron PRE, whereas pitted morningglory control and cotton yield with clomazone plus fluometuron exceeded that with the standards.
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King, Charles A., and Lawrence R. Oliver. "Application Rate and Timing of Acifluorfen, Bentazon, Chlorimuron, and Imazaquin." Weed Technology 6, no. 3 (1992): 526–34. http://dx.doi.org/10.1017/s0890037x00035740.
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Data from field studies at Fayetteville, AR, were used to predict the herbicide rate needed to provide 70, 80, or 90% control of a weed based upon weed age. Reduced herbicide rates generally needed to be applied within 6 to 12 d after emergence to control weeds 90%. Reduced rates (280 g ai ha–1or less) of acifluorfen controlled hemp sesbania, smooth pigweed, Palmer amaranth, and pitted and entireleaf morningglory 90%. Bentazon at 350 to 650 g ai ha–1controlled common cocklebur and prickly sida 90%. Common cocklebur, smooth pigweed, and pitted morningglory were controlled 90% with chlorimuron at 2 to 5 g ai ha–1and imazaquin at 20 to 80 g ai ha–1. Prickly sida and hemp sesbania were controlled 90% with imazaquin at 70 g ha–1and chlorimuron at 6 g ha–1, respectively. Barnyardgrass, large crabgrass, red rice, and sicklepod were not controlled with reduced herbicide rates.
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Vencill, William K., and Philip A. Banks. "Effects of Tillage Systems and Weed Management on Weed Populations in Grain Sorghum (Sorghum bicolor)." Weed Science 42, no. 4 (1994): 541–47. http://dx.doi.org/10.1017/s0043174500076918.
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Field research was conducted from 1987 to 1991 to evaluate the influence of four weed management systems on weed population and species dynamics in conventional-tillage and no-tillage grain sorghum production. These weed management systems included zero, low, medium, and high input systems. The weed seedbank increased faster in zero and low input weed management systems than in the high input weed management systems because of differences in weed control. Tillage influenced weed seed densities as well. Common ragweed, common lambsquarters, horseweed, and sicklepod seed densities often were greater in no-tillage than conventional-tillage plots. Common cocklebur and large crabgrass seed densities were usually greater in conventional-tillage than no-tillage plots. Smooth pigweed seed densities were not affected by tillage. Increasing weed management inputs diminished differences between tillage systems. Smooth pigweed dominated the weed populations after 4 yr in both tillage systems even in high input systems.
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Mahoney, Kris J., Christy Shropshire, and Peter H. Sikkema. "Weed Management in Conventional- and No-Till Soybean Using Flumioxazin/Pyroxasulfone." Weed Technology 28, no. 2 (2014): 298–306. http://dx.doi.org/10.1614/wt-d-13-00128.1.
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Eleven field experiments were conducted over a 3-yr period (2010, 2011, and 2012) in conventional- and no-till soybean with a flumioxazin and pyroxasulfone premix. PRE and preplant applications were evaluated for soybean injury, weed control, and yield compared to standard herbicides. Early-season soybean injury from flumioxazin/pyroxasulfone ranged from 1 to 19%; however, by harvest, soybean yields were similar across labeled rates (160 and 200 g ai ha−1), standard treatments, and the nontreated control. Flumioxazin/pyroxasulfone provided excellent control (99 to 100%) of velvetleaf, pigweed species (redroot pigweed and smooth pigweed), and common lambsquarters across almost all rates tested (80 to 480 g ai ha−1). Common ragweed, green foxtail, and giant foxtail control increased with flumioxazin/pyroxasulfone rate. The biologically effective rates varied between tillage systems. The flumioxazin/pyroxasulfone rate required to provide 80% control (R80) of pigweed was 3 and 273 g ai ha−1under conventional- and no-till, respectively. For common ragweed, the R80was 158 g ai ha−1under conventional tillage; yet, under no-till, the rate was nonestimable. The results indicate that flumioxazin/pyroxasulfone can provide effective weed control as a setup for subsequent herbicide applications.
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VanVolkenburg, Heather, Frédérique C. Guinel, and Liette Vasseur. "Impacts of Smooth Pigweed (Amaranthus hybridus) on Cover Crops in Southern Ontario." Agronomy 10, no. 4 (2020): 529. http://dx.doi.org/10.3390/agronomy10040529.
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Amaranthus hybridus is a noxious weed in Ontario, with demonstrated allelopathic properties that can lead to decreased agricultural production. We tested the germination and growth of five cover crop species exposed to A. hybridus extracts, and to dried or fresh materials in soil. A germination index was calculated, and the dry weight of plant organs were measured to quantify responses to treatments. All species had reduced germination (≤29%) in 100% extract. Trifolium pratense had significant root weight reductions in extract (52%) and dried (72%) treatments, whereas shoot weight only decreased (48%) in dried treatment. Medicago sativa shoot weight decreased (52%) in 20g fresh treatment, while root weight decreased (62%) in dried treatment. Shoot weight of Raphanus sativus increased (32%) at mid-extract concentrations, while root weight increased (33%) only with dried treatment; however, both its shoot and root weight decreased (>40%) in fresh treatment. Only the shoot weight of Lolium multiflorum increased (41% in 75% extract and 55% in dried treatment). Both Cichorium intybus shoot and root weights decreased (~50%) in fresh treatment. Crop responses to A. hybridus are complex, and material and species-dependant. Further testing in the field may provide a more comprehensive understanding of how to improve the management of A. hybridus.
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Birschbach, Eric D., Mark G. Myers, and R. Gordon Harvey. "Triazine-Resistant Smooth Pigweed (Amaranthus hybridus) Control in Field Corn (Zea maysL.)." Weed Technology 7, no. 2 (1993): 431–36. http://dx.doi.org/10.1017/s0890037x00027846.
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Studies were conducted for 3 yr to evaluate herbicides and herbicide combinations for triazine-resistant smooth pigweed (TR-AMACH) control in field corn. Of the PRE treatments, combinations of atrazine plus acetochlor, metolachlor plus dicamba, and atrazine plus alachlor provided the most complete control of this weed (77 to 81%). The best early postemergence (EP) combination was pendimethalin plus atrazine plus dicamba (93% control). Pyridate plus atrazine applied POST provided a four-site average of 98% control. The most effective sequential herbicide treatments consisted of either metolachlor or pendimethalin PRE followed by POST treatments containing either pyridate, thifensulfuron, bromoxynil, or dicamba.
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Jordan, David L., A. Stanley Culpepper, W. James Grichar, J. Tredaway Ducar, Barry J. Brecke, and Alan C. York. "Weed Control with Combinations of Selected Fungicides and Herbicides Applied Postmergence to Peanut (Arachis hypogaea L.)." Peanut Science 30, no. 1 (2003): 1–7. http://dx.doi.org/10.3146/pnut.30.1.0001.
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Abstract Experiments were conducted from 1997 through 2001 in Georgia, Florida, North Carolina, and Texas to evaluate compatibility of selected postemergence herbicides and fungicides applied in tank mixtures. Control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], goosegrass [Eleusine indica (L.) Gaertn.], large crabgrass [Digitaria sanguinalis (L.) Scop.], and Texas panicum (Panicum texanum Buckl.) by clethodim applied in tank mixtures with copper-based fungicides, fungicides containing chlorothalonil, azoxystrobin, and iprodione was reduced in 80, 69, 60, and 46% of comparisons, respectively, when compared to clethodim alone. Fluazinam, tebuconazole, and propiconazole did not reduce efficacy of clethodim. Efficacy was reduced more by fungicides when clethodim was applied in 230 L/ha spray volume compared with 94 L/ha. Efficacy of acifluorfen, bentazon, imazethapyr, and 2,4-DB applied with fungicides was also compared. Smooth pigweed (Amaranthus hybridus L.) control by 2,4-DB was reduced in at least two of three experiments when applied with chlorothalonil, copper-based fungicides, tebuconazole, azoxystrobin, and fluazinam. Iprodione did not affect efficacy of 2,4-DB. Control of smooth pigweed by imazethapyr was reduced when applied in combination with copper-based fungicides but not when applied with chlorothalonil, propiconazole, tebuconazole, fluazinam, propiconazole plus flutolanil, or propiconazole plus trifloxystrobin. Smooth pigweed control by acifluorfen was reduced in one of three experiments when applied with tebuconazole. Efficacy of acifluorfen was not affected by chlorothalonil, azoxystrobin, propiconazole, or fluazinam. Yellow nutsedge (Cyperus esculentus L.) control by bentazon was reduced by propiconazole plus chlorothalonil, propiconazole plus flutolanil, and copper-based fungicides. With the exception of fluazinam and chlorothalonil applied with 2,4-DB in one experiment, fungicides did not affect peanut injury following application of acifluorfen, clethodim, imazethapyr, or 2,4-DB.
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Trader, Brian W., Henry P. Wilson, and Thomas E. Hines. "Halosulfuron Helps Control Several Broadleaf Weeds in Cucumber and Pumpkin." Weed Technology 21, no. 4 (2007): 966–71. http://dx.doi.org/10.1614/wt-07-054.1.
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Field experiments were conducted in 1999, 2000, and 2001 to investigate PRE and POST applications of halosulfuron-methyl in combination with clomazone plus ethalfluralin for control of several broadleaf weeds in cucumber and pumpkin. Halosulfuron was applied PRE or POST to cucumber and pumpkin at 9, 18, and 27 g ai/ha in combination with a PRE application of clomazone at 175 g ai/ha plus ethalfluralin at 630 g ai/ha. Halosulfuron applied POST at 27 g/ha in combination with clomazone plus ethalfluralin controlled weed species greater than 62%. Smooth pigweed control by addition of halosulfuron at 27 g/ha PRE or POST was greater than 88%, and common ragweed control was greater than 78% PRE and 88% POST, but control of ivyleaf morningglory and tall morningglory was 43 to 67% PRE and 62 to 76% POST. Cucumber injury with addition of halosulfuron did not exceed 13% PRE or POST, but pumpkin was injured as much as 43% with addition of halosulfuron PRE and 27% by POST applications. In a separate study without clomazone plus ethalfluralin PRE, smooth pigweed up to 13 cm tall was controlled 83% by halosulfuron at 27 g/ha in 2000, but rapidly growing smooth pigweed 15 to 40 cm tall was controlled only 58% in 2001. Cucumber and pumpkin yields were not affected by halosulfuron rate but were higher than yields produced by cucumber and pumpkin treated with only the mixture of clomazone plus ethalfluralin. In these studies, cucumber and pumpkin were tolerant to halosulfuron at 9 to 27 g/ha PRE or POST, making this herbicide acceptable for use in combination with clomazone and ethalfluralin for controlling several common weed species.
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Paulsgrove, Mary D., Whitnee L. Barker, and John W. Wilcut. "Bromoxynil-Resistant Cotton and Selected Weed Response to Mixtures of Bromoxynil and Pyrithiobac." Weed Technology 19, no. 3 (2005): 753–61. http://dx.doi.org/10.1614/wt-04-306r.1.
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An experiment was conducted at four locations in North Carolina in 1996 and 1997 to evaluate weed control and cotton response in conventional-tillage bromoxynil-resistant cotton. Weed management systems evaluated included a factorial arrangement of bromoxynil postemergence (POST) at 0, 0.28, 0.42, or 0.56 kg ai/ha in mixture with pyrithiobac POST at 0, 0.018, 0.032, or 0.072 kg ai/ha. Additional treatments evaluated included trifluralin preplant-incorporated (PPI) plus fluometuron preemergence (PRE). All systems received a postemergence-directed (PDS) treatment of fluometuron plus MSMA. Bromoxynil at 0.42 kg/ha POST followed by (fb) fluometuron plus MSMA PDS controlled common lambsquarters, common ragweed, eclipta, prickly sida, redroot pigweed, spurred anoda; and entireleaf, ivyleaf, pitted, and tall morningglory at least 93%, whereas smooth pigweed and volunteer peanut were controlled 73 and 86%, respectively. Pyrithiobac at 0.036 kg/ha POST fb fluometuron plus MSMA PDS controlled eclipta, common ragweed, prickly sida, redroot, and smooth pigweed, and spurred anoda at least 94%. Volunteer peanut was controlled 84% by pyrithiobac at 0.032 kg/ha, whereas pitted, ivyleaf, and entireleaf morningglory were controlled by 63, 78, and 83%, respectively. Pyrithiobac at 0.072 kg/ha fb fluometuron plus MSMA PDS controlled common lambsquarters 48%. Cotton yield with bromoxynil plus pyrithiobac POST mixtures were equivalent to trifluralin PPI plus fluometuron PRE at three locations and better at the fourth location. Bromoxynil-resistant cotton ‘47’ and ‘57’ had excellent tolerance to all POST herbicide treatments.
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Myers, Matthew W., William S. Curran, Mark J. Vangessel, et al. "Effect of Soil Disturbance on Annual Weed Emergence in the Northeastern United States." Weed Technology 19, no. 2 (2005): 274–82. http://dx.doi.org/10.1614/wt-03-242r1.
Full textAbstract:
A 2-yr experiment evaluated the effect of spring soil disturbance on the periodicity of weed emergence. At four locations across the northeastern United States, emerged weeds, by species, were monitored every 2 wk in both undisturbed plots and plots tilled in the spring with a rotary cultivator. Eight weed species including large crabgrass, giant and yellow foxtail, common lambsquarters, smooth pigweed, eastern black nightshade, common ragweed, and velvetleaf occurred at three or more site-years. Spring soil disturbance either had no effect or reduced total seedling emergence compared with undisturbed soils. Total seedling emergence for large crabgrass, giant foxtail, smooth pigweed, and common ragweed were on average, 1.4 to 2.6 times less with spring soil disturbance, whereas eastern black nightshade and velvetleaf were mostly unaffected by the soil disturbance. The influence of soil disturbance on yellow foxtail and common lambsquarters emergence varied between seasons and locations. Although the total number of emerged seedlings was often affected by the soil disturbance, with the exception of yellow foxtail and common ragweed, the periodicity of emergence was similar across disturbed and undisturbed treatments.
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Poston, Daniel H., Cecilia Mucha Hirata, and Henry P. Wilson. "Response of acetolactate synthase from imidazolinone-susceptible and -resistant smooth pigweed toALS inhibitors." Weed Science 50, no. 3 (2002): 306–11. http://dx.doi.org/10.1614/0043-1745(2002)050[0306:roasfi]2.0.co;2.
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Silva, Daniel Valadão, Cassia Michelle Cabral, Evander Alves Ferreira, Felipe Paolinelli de Carvalho, José Barbosa dos Santos, and Jeferson Luiz Dallabona Dombroski. "Anatomical adaptations to different soil moisture contents in palisade grass and smooth pigweed." Revista Ceres 65, no. 4 (2018): 306–13. http://dx.doi.org/10.1590/0034-737x201865040002.
Full textAbstract:
ABSTRACT Weed adaptations to different environments contribute to their success in establishing in different agroecosystems. A greenhouse and laboratory study was carried out to evaluate the effects of different levels of soil moisture on the anatomical characteristics of two weed species. The treatments were arranged in a 2 x 5 factorial design, with the first factor representing the weed species (Amaranthus hybridus and Brachiaria brizantha) and the second factor being the soil moisture levels in which they were grown (100%, 80%, 74%, 67%, and 60% of field capacity). At 55 days after weed emergence, the material for anatomical evaluations was collected. The water stress affected the two weed species differently, causing changes both in the thickness of the tissues evaluated and in their proportions. These changes seem to be related to how each species tolerates water stress. A. hybridus showed thickening of all leaf tissue and change in the proportion of these tissues, whereas B. brizantha showed a decrease in thickness of the leaf tissue and an increase in the proportion of adaxial epidermal and parenchymal tissues.
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Jordan, Nicholas. "Effects of the Triazine-Resistance Mutation on Fitness in Amaranthus hybridus (Smooth Pigweed)." Journal of Applied Ecology 33, no. 1 (1996): 141. http://dx.doi.org/10.2307/2405023.
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Whaley, Cory M., Henry P. Wilson, and James H. Westwood. "A New Mutation in PlantALSConfers Resistance to Five Classes of ALS-Inhibiting Herbicides." Weed Science 55, no. 2 (2007): 83–90. http://dx.doi.org/10.1614/ws-06-082.1.
Full textAbstract:
Experiments were conducted to evaluate a biotype of smooth pigweed that had survived applications of sulfonylurea (SU) and imidazolinone (IMI) herbicides in a single season. The source field had a history of repeated acetolactate synthase (ALS)-inhibiting herbicide use over several years. Whole-plant response experiments evaluated the resistant (R11) biotype and an ALS-inhibitor susceptible (S) smooth pigweed biotype to herbicides from the SU, IMI, pyrimidinylthiobenzoate (PTB), and triazolopyrimidine sulfonanilide (TP) chemical families. The R11 biotype exhibited 60- to 3,200-fold resistance to all four ALS-Inhibiting herbicide chemistries compared with the S biotype. Nucleotide sequence comparison ofALSgenes from R11 and S biotypes revealed a single nucleotide difference that resulted in R11 having an amino acid substitution of aspartate to glutamate at position 376, as numbered relative to the protein sequence of mouseearcress. This is the first report of an amino acid substitution at this position of anALSgene isolated from a field-selected weed biotype. To verify the role of this mutation in herbicide resistance, theALSgene was cloned and expressed inArabidopsis. TransgenicArabidopsisexpressing thisALSgene exhibited resistance to SU, IMI, PTB, TP, and sulfonylaminocarbonyltriazolinone ALS-Inhibiting herbicide classes.
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Walters, S. Alan, Scott A. Nolte, and Bryan G. Young. "Influence of Winter Rye and Preemergence Herbicides on Weed Control in No-tillage Zucchini Squash Production." HortTechnology 15, no. 2 (2005): 238–43. http://dx.doi.org/10.21273/horttech.15.2.0238.
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The influence of `Elbon', `Maton', and `Wheeler' winter rye (Secale cereale) with or without herbicide treatments on weed control in no-tillage (NT) zucchini squash (Cucurbita pepo) was determined. `Elbon' or `Maton' produced higher residue biomass, greater soil coverage, and higher weed control compared with `Wheeler'. Although winter rye alone did not provide sufficient weed control (generally <70%), it provided substantially greater redroot pigweed (Amaranthus retroflexus) and smooth crabgrass (Digitaria ischaemum) control (regardless of cultivar used) compared with no winter rye at both 28 and 56 days after transplanting (DAT). No effect (P > 0.05) of winter rye cultivar on early or total squash yield was detected. Although applying clomazone + ethalfluralin to winter rye residues improved redroot pigweed control compared with no herbicide, the level of control was generally not adequate (<85% control) by 56 DAT. Treatments that included halosulfuron provided greater control of redroot pigweed than clomazone + ethalfluralin, and redroot pigweed control from halosulfuron treatments was similar to the weed-free control. However, regardless of year or cover crop, any treatment with halosulfuron caused unacceptable injury to zucchini squash plants which lead to reduced squash yield (primarily early yields). Insignificant amounts of squash injury (<10% due to stunting) resulted from clomazone + ethalfluralin in no-tillage plots during either year. Treatments with clomazone + ethalfluralin had early and total yields that were similar to those of the weed-free control, although this herbicide combination provided less weed control compared with the weed-free control.