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Clarence J. Swanton - One of the best experts on this subject based on the ideXlab platform.
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predispersal seed predation of redroot Pigweed amaranthus retroflexus
Weed Science, 2003Co-Authors: Nancy Desousa, Jason T Griffiths, Clarence J. SwantonAbstract:Abstract Field experiments were conducted in 1999 and 2000 to determine if (1) seed predation of redroot Pigweed plants occurred in agricultural fields, (2) corn-cropping patterns could be manipulated to influence the quantity of weed seed predation, and (3) alterations in corn canopies affected the microenvironment, possibly influencing predator populations. Corn was planted in standard (75 cm) or narrow (37.5 cm) rows with corn population densities ranging from low to very high (2.5 to 10 plants m−2). The extent of seed predation occurring on terminal weed inflorescences in the treatments was evaluated. Predation levels of redroot Pigweed were highly variable spatially and temporally. Coleophora lineapulvella Chambers (Lepidoptera: Coleophoridae) was the dominant predator of redroot Pigweed seed. Seed predation was higher in 2000 than in 1999 (P < 0.05). On average, C. lineapulvella larvae attacked 11% of the inflorescences in 2000 and 3% of inflorescences in 1999. The proportion of damaged seeds per at...
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Effects of photoperiod on the phenological development of redroot Pigweed (Amaranthus retroflexus L.)
Canadian Journal of Plant Science, 2000Co-Authors: Jian Zhong Huang, William Deen, Anil Shrestha, Matthijs Tollenaar, Hamid Rahimian, Clarence J. SwantonAbstract:Mechanistic weed models focus on determining the outcome of weed and crop interference. An understanding of weed phenology is essential for simulation model development. Phenological development is a major factor determining the outcome of weed–crop competition. Growth cabinet studies were conducted to characterize the influence of photoperiod on the phenological development of redroot Pigweed (Amaranthus retroflexus L.). Results indicated that redroot Pigweed is a quantitative short-day species. Four development phases of redroot Pigweed were described according to its response to photoperiod: (1) a juvenile phase of 1.1 d; (2) a photoperiod-sensitive inductive phase of 7.9 d; (3) a photoperiod-sensitive post-inductive phase of 39.9 d; and (4) a photoperiod-insensitive phase of 2.2 d. This information is useful for the development of mechanistic models and for comprehending the distribution and competitive ability of redroot Pigweed with crops. The utilization of these results could help in predicting th...
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interference between Pigweed amaranthus spp barnyardgrass echinochloa crus galli and soybean glycine max
Weed Science, 1998Co-Authors: Paul Cowan, Susan E Weaver, Clarence J. SwantonAbstract:Field experiments were conducted to determine the influence of time of emergence and density of single and multispecies populations of Pigweed and barnyardgrass on soybean yield and competitive abilities of Pigweed and barnyardgrass. Pigweed and barnyardgrass were established at selected densities within 12.5 cm on either side of the soybean row. Pigweed and barnyardgrass seeds were sown concurrently with soybean and at the cotyledon stage of soybean growth. Time and density of Pigweed and barnyardgrass seedling emergence relative to soybean influenced the magnitude of soybean yield loss. Maximum soybean yield loss ranged from 32 to 99%, depending upon time of emergence relative to soybean. Pigweed was more competitive than barnyardgrass across all locations, years, and time of weed emergence. When Pigweed was assigned a competitive index of 1 on a scale from 0 to 1, the competitive ability of barnyardgrass ranged from 0.075 to 0.40 of Pigweed, depending upon location and time of emergence. This is the first multiple weed species study to include time of weed emergence relative to the crop. Competitive index values for multiple weed species must be calculated from field experiments in which weeds are grown with the crop under differing environmental conditions.
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temperature and moisture dependent models of seed germination and shoot elongation in green and redroot Pigweed amaranthus powellii a retroflexus
Weed Science, 1997Co-Authors: J O E Oryokot, Stephen D Murphy, A G Thomas, Clarence J. SwantonAbstract:To predict weed emergence and help farmers make weed management decisions, we constructed a mathematical model of seed germination for green and redroot Pigweed based on temperature and water potential (moisture) and expressing cumulative germination in terms of thermal time (degree days). Empirical observations indicated green Pigweed germinated at a lower base temperature than redroot Pigweed but the germination rate of redroot Pigweed is much faster as mean temperature increases. Moisture limitation delayed seed germination until 23.8 C (green Pigweed) or 27.9 (redroot Pigweed); thereafter, germination was independent of water potential as mean temperatures approached germination optima. Our germination model, based on a cumulative normal distribution function, accounted for 80 to 95% of the variation in seed germination and accurately predicted that redroot Pigweed would have a faster germination rate than green Pigweed. However, the model predicted that redroot Pigweed would germinate before green Pigweed (in thermal time) and was generally less accurate during the early period of seed germination. The model also predicted that moisture limitation would increase, rather than delay, seed germination. These errors were related to the mathematical function chosen and analyses used, but an explicit interaction term for water potential and temperature is also needed to produce an accurate model. We also tested the effect of mean temperature on shoot elongation (emergence) and described the relationship by a linear model. Base temperatures for shoot elongation were higher than for seed germination. Shoot elongation began at 15.6 and 14.4 C for green and redroot Pigweed, respectively; they increased linearly with temperature until the optimum of 27.9 C was reached. Elongation was dependent on completion of the rate-limiting step of radicle emergence and was sensitive to temperature but not moisture; hence, elongation was sensitive to a much smaller temperature range. Beyond mathematical changes, we are testing our model in the field and need to link it to ecophysiological, genetic, and spatially explicit population processes for it to be useful in decision support for weed management.
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effect of tillage and corn on Pigweed amaranthus spp seedling emergence and density
Weed Science, 1997Co-Authors: Joseph O E Oryokot, Stephen D Murphy, Clarence J. SwantonAbstract:We studied the effect of no-till, chisel, and moldboard plow and the presence or absence of corn on soil temperature, moisture and, subsequently, the emergence phenology and density of Pigweed seedlings at 2 sites from 1993 to 1995 inclusively. Tillage significantly affected the phenology of Pigweed seedling emergence only during a June drought at one site in 1994. Soil temperature and moisture, measured at 2.5-cm depths, also were unaffected by tillage. Weed phenology is usually earlier in no-till because more seeds are located closer to the surface (< 5 cm deep) in no-till, thereby reducing the delay in penetrating through the soil, and because soil temperatures and moisture are nearer the germination and emergence optima. However, Pigweed seedlings are already physiologically restricted to germination depths of less than 2.5 cm regardless of tillage; therefore, this prior constraint eliminated any potential differences in emergence phenologies caused by tillage. The presence or absence of corn also did not affect soil temperatures, soil moisture, or Pigweed seedling emergence phenologies. Pigweed seedling density was significantly higher in no-till; this may have been caused by increased numbers of seeds near the soil surface in no-till. The presence or absence of corn did not affect Pigweed seedling density; the lack of a significant effect probably reflects high variances in density. Although necessary for most weed species, tillage may be a less important factor to consider in predicting Pigweed population dynamics and subsequent management recommendations.
Allan T. Showler - One of the best experts on this subject based on the ideXlab platform.
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plant responses to water deficit and shade stresses in Pigweed and their influence on feeding and oviposition by the beet armyworm lepidoptera noctuidae
Environmental Entomology, 2005Co-Authors: Patrick J Moran, Allan T. ShowlerAbstract:Water deficit and shade stress in weed-infested crops could alter plant growth and biochemistry and feeding and oviposition by the beet armyworm, Spodoptera exigua Hubner. Palmer amaranth Pigweed, Amaranthus palmeri S. Wats., was grown under 25% of full watering (water deficit), 30% of full light (shade), or combined stress. All treatments decreased plant height and weight. Shade and combined stresses decreased leaf counts and increased leaf water content. Water deficit stress increased leaf water potential, soluble protein and carbohydrate contents, peroxidase activities, and accumulations of 10 individual free amino acids (FAAs), summed essential FAAs, and total FAAs. Combined stress increased water potential, soluble carbohydrates, 12 individual FAAs, summed essential FAAs, and total FAAs. Shade stress decreased water potential, soluble carbohydrates, seven individual FAAs, and essential FAAs. Beet armyworm larvae consumed similar leaf areas on water deficit–stressed and nonstressed plants and larger areas on plants grown under shade or combined stress. Larval survival was reduced, and time to pupation was higher on shade-stressed leaves. Adult females deposited more eggs on shade and combined stress plants and fewer eggs on water deficit-stressed plants compared with controls. Beet armyworm feeding and oviposition responded to variation in water content. Stress-induced changes in nutrients were not tied to insect preference but could have negatively influenced survival under shade stress. The results have implications for the plant stress hypothesis and for the use of Pigweeds for beet armyworm detection.
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Spodoptera exigua Oviposition and Larval Feeding Preferences for Pigweed, Amaranthus hybridus, over Squaring Cotton, Gossypium hirsutum, and a Comparison of Free Amino Acids in Each Host Plant
Journal of chemical ecology, 2001Co-Authors: Allan T. ShowlerAbstract:The beet armyworm, Spodoptera exigua (Hubner), can utilize a number of different host plants for oviposition and larval development, but some host plants are preferred over others. This study, using cage choice tests and olfactometer assays, demonstrates the beet armyworm's preference for Pigweed, Amaranthus hybridus L., over cotton, Gossypium hirsutum L. Cage and olfactometer choice assays indicated that olfaction plays an important role in host selection by ovipositing females. First instars exhibited no feeding preference, but the more mobile third instars showed a significant feeding preference for excised Pigweed leaves. The higher quantities and more diverse accumulations of free amino acids in Pigweed might, in conjunction with other physiochemical and mechanical attractant and deterrent factors in the two-plant species system, play roles in the tendency of the beet armyworm to select Pigweed over cotton and in providing a superior array of easily absorbed amino acids as compared to cotton.
William M. Stall - One of the best experts on this subject based on the ideXlab platform.
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optimum densities of three leguminous cover crops for suppression of smooth Pigweed amaranthus hybridus
Weed Science, 2008Co-Authors: Amanda S Collins, William M. Stall, Carlene A Chase, Chad M HutchinsonAbstract:Abstract 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 ...
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competitiveness of three leguminous cover crops with yellow nutsedge cyperus esculentus and smooth Pigweed amaranthus hybridus
Weed Science, 2007Co-Authors: Amanda S Collins, William M. Stall, Carlene A Chase, Chad M HutchinsonAbstract:Abstract 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 l...
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Aggressivity: Cucumber vs. Amaranth1
Weed Technology, 2006Co-Authors: Adrian D. Berry, Gregory E Macdonald, William M. Stall, Bala Rathinasabapathi, R. CharudattanAbstract: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 dat...
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smooth Pigweed amaranthus hybridus l and livid amaranth amaranthus lividus interference with cucumber cucumis sativus 1
Weed Technology, 2006Co-Authors: Adrian D. Berry, Gregory E Macdonald, William M. Stall, Bala Rathinasabapathi, R. CharudattanAbstract: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 m2 caused 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. Nomenclature: Smooth Pigweed, Amaranthus hybridus #3 AMACH; livid amaranth, Amaranthus lividus # AMALI; cucumber, Cucumis sativus L. Additional index words: Additive experiment, amaranth, cucumber, weed competition, yield loss.
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phosphorus absorption in lettuce smooth Pigweed amaranthus hybridus and common purslane portulaca oleracea mixtures
Weed Science, 2004Co-Authors: Bielinski M Santos, William M. Stall, Joan A Dusky, Donn G Shilling, Thomas A Bewick, James P GilreathAbstract:Abstract Greenhouse studies were conducted to determine the influence of phosphorus (P) concentrations on the growth of lettuce, smooth Pigweed, and common purslane in monocultures and in mixtures and to determine the P-absorption rate of each species over time. For the P-competition studies, lettuce–smooth Pigweed and lettuce–common purslane mixtures were established in P-less hydroponic solutions. Each lettuce–weed mixture was established separately. Concentrations of P were 10, 20, 40, 80, and 160 mg L−1. Lettuce to weed planting proportions were 2:0, 0:2, and 1:1. In the mixtures, biomass of common purslane increased sharply between 10 and 20 mg P L−1, depressing lettuce growth. No biomass changes were observed in smooth Pigweed as P concentration increased. However, both weeds increased their P content within this range, depriving lettuce of this nutrient. Common purslane competed for P for its own growth, whereas smooth Pigweed absorbed P luxuriously. For the P-absorption studies, roots of lettuce, ...
Michael J. Horak - One of the best experts on this subject based on the ideXlab platform.
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interference of redroot Pigweed amaranthus retroflexus palmer amaranth a palmeri and common waterhemp a rudis in soybean
Weed Science, 2003Co-Authors: Curtis N Bensch, Michael J. Horak, Dallas E PetersonAbstract:Abstract Field studies were conducted in 1997 and 1998 at Manhattan and Topeka, KS, to examine the competitive effects of redroot Pigweed, Palmer amaranth, and common waterhemp on soybean yield. The experiments were established as a randomized complete block design in a factorial arrangement of three Pigweed species, two Pigweed planting dates (soybean planting and cotyledon stage), and seven weed densities (0.25, 0.5, 1, 2, 4, and 8 plants m−1 of row, plus a weed-free control). The effect of weed density on soybean yield loss, Pigweed biomass, and Pigweed seed production were described using a rectangular hyperbola model. Soybean yield loss varied between locations depending on the weed species, density, and time of emergence. Yield loss increased with weed density for each species and location with the first Pigweed emergence time. The maximum soybean yield loss occurred at the first planting and 8 plants m−1 of row density, and was 78.7, 56.2, and 38.0% as determined by the model for Palmer amaranth, c...
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Relative time of redroot Pigweed emergence affects dry matter partitioning
Weed Science, 2001Co-Authors: Stevan Z. Knezevic, R. L. Vanderlip, Michael J. HorakAbstract:Abstract The partitioning coefficient is defined as the proportion of new dry matter partitioned among different plant parts. Partitioning coefficients can be used to model plant dry matter accumulation. In 1994 and 1995, field studies were conducted at two locations near Manhattan, KS, to determine the influence of density and relative time of emergence of redroot Pigweed on dry matter partitioning to stem, leaves, and reproductive parts throughout the season. Redroot Pigweed was grown with sorghum and in monoculture at densities of 2, 4, and 12 plants m−1 of row each year at each location. Dry matter partitioning during vegetative growth was not influenced by plant density. However, partition coefficients during the reproductive growth stage changed as a linear function of the time of Pigweed emergence relative to the sorghum leaf stage. The later the emergence time relative to sorghum leaf stage, the higher the partitioning coefficient values for leaf (PCleaf) and stem (PCstem) and the lower the partit...
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influence of emergence time and density on redroot Pigweed amaranthus retroflexus
Weed Science, 1998Co-Authors: Stevan Z. Knezevic, Michael J. HorakAbstract:Field studies were conducted at two locations near Manhattan, KS, in 1994 and 1995 to determine the influence of density (0.5, 1, 2, 4, and 12 plants m−1 row) and time of emergence on redroot Pigweed growth in monoculture or with sorghum. Redroot Pigweed was seeded at sorghum planting and at the three- to four-leaf stage of sorghum in plots with sorghum or alone. When redroot Pigweed grew with sorghum, dry matter and seed production were reduced with later times of emergence. In monoculture, there was no reduction in dry matter or seed number between the emergence dates studied. Redroot Pigweed dry matter and seed production per plant were reduced as plant density increased for plants grown in monoculture. The same trend was observed for redroot Pigweed grown with sorghum that did not emerge early relative to sorghum. Plants grown at low density exhibited more lateral growth than when grown at higher densities because of intraspecific competition.
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influence of emergence time and density on redroot Pigweed amaranthus retroflexus
Weed Science, 1998Co-Authors: Stevan Z. Knezevic, Michael J. HorakAbstract:Michael J. Horak Corresponding author. Department of Agronomy, Kansas State University, Manhattan, KS 665065501; mjhorak@ksu.edu Field studies were conducted at two locations near Manhattan, KS, in 1994 and 1995 to determine the influence of density (0.5, 1, 2, 4, and 12 plants m-1 row) and time of emergence on redroot Pigweed growth in monoculture or with sorghum. Redroot Pigweed was seeded at sorghum planting and at the threeto four-leaf stage of sorghum in plots with sorghum or alone. When redroot Pigweed grew with sorghum, dry matter and seed production were reduced with later times of emergence. In monoculture, there was no reduction in dry matter or seed number between the emergence dates studied. Redroot Pigweed dry matter and seed production per plant were reduced as plant density increased for plants grown in monoculture. The same trend was observed for redroot Pigweed grown with sorghum that did not emerge early relative to sorghum. Plants grown at low density exhibited more lateral growth than when grown at higher densities because of intraspecific competition.
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relative time of redroot Pigweed amaranthus retroflexus l emergence is critical in Pigweed sorghum sorghum bicolor l moench competition
Weed Science, 1997Co-Authors: Stevan Z. Knezevic, Michael J. Horak, R. L. VanderlipAbstract:Redroot Pigweed is a common weed in sorghum fields throughout the southcentral United States including Kansas. In 1994 and 1995, field studies were conducted at two sites near Manhattan, KS, to determine the influence of redroot Pigweed densities and times of emergence on sorghum yield and yield components. Redroot Pigweed was sown at densities of 0.5, 1, 2, 4, and 12 plants meter−1 of row within a 25-cm band over the sorghum row at planting and at the three- to four-leaf stage of sorghum. A rectangular hyperbola was used to describe the relationship between crop yield loss and weed density. Because of the instability of both coefficients I (percentage yield loss at low weed density) and A (percentage yield loss at high weed density), our results do not support the use of a model based exclusively on weed number to estimate sorghum yield loss across all locations within a region. A quadratic polynomial equation that accounts for the time of weed emergence relative to the crop growth stage is suggested as an alternative method to estimate sorghum yield loss. At the densities studied, the time of Pigweed emergence relative to the sorghum leaf stage was critical for the outcome of sorghum-Pigweed competition. Significant sorghum yield losses occurred only when Pigweed emerged before the 5.5-leaf stage of sorghum. An examination of yield components suggested that the yield loss was a result of a reduction in number of seeds per head.
Stevan Z. Knezevic - One of the best experts on this subject based on the ideXlab platform.
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Relative time of redroot Pigweed emergence affects dry matter partitioning
Weed Science, 2001Co-Authors: Stevan Z. Knezevic, R. L. Vanderlip, Michael J. HorakAbstract:Abstract The partitioning coefficient is defined as the proportion of new dry matter partitioned among different plant parts. Partitioning coefficients can be used to model plant dry matter accumulation. In 1994 and 1995, field studies were conducted at two locations near Manhattan, KS, to determine the influence of density and relative time of emergence of redroot Pigweed on dry matter partitioning to stem, leaves, and reproductive parts throughout the season. Redroot Pigweed was grown with sorghum and in monoculture at densities of 2, 4, and 12 plants m−1 of row each year at each location. Dry matter partitioning during vegetative growth was not influenced by plant density. However, partition coefficients during the reproductive growth stage changed as a linear function of the time of Pigweed emergence relative to the sorghum leaf stage. The later the emergence time relative to sorghum leaf stage, the higher the partitioning coefficient values for leaf (PCleaf) and stem (PCstem) and the lower the partit...
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influence of emergence time and density on redroot Pigweed amaranthus retroflexus
Weed Science, 1998Co-Authors: Stevan Z. Knezevic, Michael J. HorakAbstract:Field studies were conducted at two locations near Manhattan, KS, in 1994 and 1995 to determine the influence of density (0.5, 1, 2, 4, and 12 plants m−1 row) and time of emergence on redroot Pigweed growth in monoculture or with sorghum. Redroot Pigweed was seeded at sorghum planting and at the three- to four-leaf stage of sorghum in plots with sorghum or alone. When redroot Pigweed grew with sorghum, dry matter and seed production were reduced with later times of emergence. In monoculture, there was no reduction in dry matter or seed number between the emergence dates studied. Redroot Pigweed dry matter and seed production per plant were reduced as plant density increased for plants grown in monoculture. The same trend was observed for redroot Pigweed grown with sorghum that did not emerge early relative to sorghum. Plants grown at low density exhibited more lateral growth than when grown at higher densities because of intraspecific competition.
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influence of emergence time and density on redroot Pigweed amaranthus retroflexus
Weed Science, 1998Co-Authors: Stevan Z. Knezevic, Michael J. HorakAbstract:Michael J. Horak Corresponding author. Department of Agronomy, Kansas State University, Manhattan, KS 665065501; mjhorak@ksu.edu Field studies were conducted at two locations near Manhattan, KS, in 1994 and 1995 to determine the influence of density (0.5, 1, 2, 4, and 12 plants m-1 row) and time of emergence on redroot Pigweed growth in monoculture or with sorghum. Redroot Pigweed was seeded at sorghum planting and at the threeto four-leaf stage of sorghum in plots with sorghum or alone. When redroot Pigweed grew with sorghum, dry matter and seed production were reduced with later times of emergence. In monoculture, there was no reduction in dry matter or seed number between the emergence dates studied. Redroot Pigweed dry matter and seed production per plant were reduced as plant density increased for plants grown in monoculture. The same trend was observed for redroot Pigweed grown with sorghum that did not emerge early relative to sorghum. Plants grown at low density exhibited more lateral growth than when grown at higher densities because of intraspecific competition.
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relative time of redroot Pigweed amaranthus retroflexus l emergence is critical in Pigweed sorghum sorghum bicolor l moench competition
Weed Science, 1997Co-Authors: Stevan Z. Knezevic, Michael J. Horak, R. L. VanderlipAbstract:Redroot Pigweed is a common weed in sorghum fields throughout the southcentral United States including Kansas. In 1994 and 1995, field studies were conducted at two sites near Manhattan, KS, to determine the influence of redroot Pigweed densities and times of emergence on sorghum yield and yield components. Redroot Pigweed was sown at densities of 0.5, 1, 2, 4, and 12 plants meter−1 of row within a 25-cm band over the sorghum row at planting and at the three- to four-leaf stage of sorghum. A rectangular hyperbola was used to describe the relationship between crop yield loss and weed density. Because of the instability of both coefficients I (percentage yield loss at low weed density) and A (percentage yield loss at high weed density), our results do not support the use of a model based exclusively on weed number to estimate sorghum yield loss across all locations within a region. A quadratic polynomial equation that accounts for the time of weed emergence relative to the crop growth stage is suggested as an alternative method to estimate sorghum yield loss. At the densities studied, the time of Pigweed emergence relative to the sorghum leaf stage was critical for the outcome of sorghum-Pigweed competition. Significant sorghum yield losses occurred only when Pigweed emerged before the 5.5-leaf stage of sorghum. An examination of yield components suggested that the yield loss was a result of a reduction in number of seeds per head.
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relative time of redroot Pigweed amaranthus retroflexus l emergence is critical in Pigweed sorghum sorghum bicolor l moench competition
Weed Science, 1997Co-Authors: Stevan Z. Knezevic, Michael J. Horak, R. L. VanderlipAbstract:Michael J. Horak Richard L. Vanderlip Department of Agronomy, Kansas State University, Manhattan, KS 66506-5501 Redroot Pigweed is a common weed in sorghum fields throughout the southcentral United States including Kansas. In 1994 and 1995, field studies were conducted at two sites near Manhattan, KS, to determine the influence of redroot Pigweed densities and times of emergence on sorghum yield and yield components. Redroot Pigweed was sown at densities of 0.5, 1, 2, 4, and 12 plants meter-1 of row within a 25-cm band over the sorghum row at planting and at the threeto four-leaf stage of sorghum. A rectangular hyperbola was used to describe the relationship between crop yield loss and weed density. Because of the instability of both coefficients I (percentage yield loss at low weed density) and A (percentage yield loss at high weed density), our results do not support the use of a model based exclusively on weed number to estimate sorghum yield loss across all locations within a region. A quadratic polynomial equation that accounts for the time of weed emergence relative to the crop growth stage is suggested as an alternative method to estimate sorghum yield loss. At the densities studied, the time of Pigweed emergence relative to the sorghum leaf stage was critical for the outcome of sorghum-Pigweed competition. Significant sorghum yield losses occurred only when Pigweed emerged before the 5.5-leaf stage of sorghum. An examination of yield components suggested that the yield loss was a result of a reduction in number of seeds per head.
