Showing papers in "Weed Science in 1985"
TL;DR: Multiple regression analysis of data from field experiments conducted in Alberta between 1972 and 1983 indicated that there was a significant relation- ship between yield loss of barley and wheat and relative time of emergence of wild oat andWild oat density.
Abstract: Multiple regression analysis of data from field experiments conducted in Alberta at two locations between 1972 and 1983 indicated that there was a significant relation- ship between yield loss of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) and relative time of emergence of wild oat (Avena fatua L. #4 AVEFA). At a given wild oat density, percent yield loss increased the earlier wild oat emerged relative to the crops and gradually diminished the later it emerged. However, the magnitude of the yield loss for both species varied with the year. Regression equations based on data pooled over years and locations were developed to provide an estimate of yield loss of barley and wheat due to relative time of wild oat emergence and wild oat density. The information should be considered when barley and wheat losses due to wild oat are being assessed. Additional index words. Index of competition, wild oat density, AVEFA.
241 citations
TL;DR: The field surveys were conducted late in thegrowing season before harvest commenced; hence, the weed populations consisted of species that had been present during the early part of the growing season and may have contributed to yield losses.
Abstract: A weed survey system methodology was developed and used annually for 4 yr in the province of Saskatchewan. Based on a stratified random sampling procedure, fields were selected in wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), rye (Secale cereale L.), rape (Brassica napus L., Brassica campestris L.), and flax (Linum usitatissimum L.) crops. The boundaries of the 43 agricultural extension districts in the province formed the strata. The provincial agricultural extension service provided staff to conduct the survey. Computer processing of the data enabled reports, containing summary tables and dis- tribution maps, to be distributed to extension, research, and industry personnel within 3 months after completion of the field survey. The field surveys were conducted late in the growing season before harvest commenced; hence, the weed populations consisted of species that had been present during the early part of the growing season and may have contributed to yield losses. During the 4 yr of the survey, weeds were counted in 4423 fields. Of the 164 species re- corded, 97 species occurred in more than three fields. Only 29 species were encountered frequently in the fields. Green foxtail (Setaria viridis (L.) Beauv. #3 SETVI), wild buck- wheat (Polygonum convolvulus L. # POLCO), and wild oat (Avena fatua L. # AVEFA) were the top three species based on a ranking system using a measure called relative abun-
190 citations
TL;DR: The world distributions of yellow starthistle and Russian knapweed are mapped based on in- formation from world regional floras based on surveys made in the United States and the extent of the infestations and economic importance of these weeds was determined.
Abstract: The world distributions of yellow starthistle (Centaurea solstitialis L. #3 CENSO) and Russian knapweed (Centaurea repens L. # CENRE) are mapped based on in- formation from world regional floras. A survey of weed specialists and herbaria was made in the United States, and the extent of the infestations and economic importance of these weeds was determined for the 48 contiguous states. Yellow starthistle currently occurs in 209 counties in 23 states and has apparently increased in abundance since 1970. Russian knapweed was reported in 412 counties in 21 states and does not seem to be spreading. Both of these weedy plant species are of greater economic importance in the western United States than in the east. Additional index words. Plant distribution, weedy thistles, CENSO, CENRE.
137 citations
TL;DR: Alachlor and metolachlor adsorption was positively correlated with soil organic-matter content, clay content, and surface area as measured by ethylene glycol monoethyl ether (EGME) or benzyl ethyl ether (BEE) and inversely correlated with herbicidal activity as mentioned in this paper.
Abstract: Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] adsorption was positively correlated with soil organic-matter content, clay content, and surface area as measured by ethylene glycol monoethyl ether (EGME) or benzyl ethyl ether (BEE) and inversely correlated with herbicidal activity. Alachlor was adsorbed in slightly greater amounts by soil than metolachlor. Metolachlor had slightly greater bioactivity than alachlor on grass weeds, but the herbicides had similar activity on broadleaf weeds. Slightly greater amounts of metolachlor than alachlor were leached through a Norfolk soil and slightly greater amounts of alachlor were retained in the upper soil zones, compared with metolachlor.
131 citations
TL;DR: In this article, field experiments were conducted to measure the grain yield of wheat (Triticum aestivum L. 'ANZA') at various wild oat (Avena fatua L. #3 AVEFA) and wheat plant densities.
Abstract: Field experiments were conducted to measure the grain yield of wheat (Triticum aestivum L. 'ANZA') at various wild oat (Avena fatua L. #3 AVEFA) and wheat plant densities. Wheat yield declined as wild oat plant density increased. Wheat yield increased in wild oat-infested plots as wheat plant density increased. Regression models were developed to describe the combined effect of wheat and wild oat plant densities on wheat grain yield. Wheat yields were best described by a nonlinear regression model using the relative density of wild oat in the weed-crop stand as the dependent variable. Inclusion of crop stand as a com- petitive factor significantly improved the fit of all regression models tested. Wild oat were more competitive against wheat in these experiments than in experiments reported by others. Possible reasons for differences in observed competitiveness are discussed. Additional index words. Interference, grain yield, AVEFA.
127 citations
TL;DR: In this paper, the half-life of chlorsulfuron was investigated on four soils having different pH values (6.2 to 8.1) and the extent of adsorption was found to be greater at 8 than at 30 C.
Abstract: Adsorption of chlorsulfuron {2-chloro-N[[(4methoxy -6methyl1,3,5 -triazin-2 yl) aminol carbonyl] ben zenesulfonamide} on four soils having different pH values (6.2 to 8.1) was low. Log/log Freundlich isotherms for all soils at 8 and 30 C were linear, the extent of adsorption being greater at 8 than at 30 C. There was an inverse relationship between pH and degradation rate with a half-life of 88.5 days at pH 6.2 and 144 days at pH 8.1 at 20 C. Rapid disappearance was noted during the first 15 days after application. With decreasing moisture and temperature, chlorsulfuron degraded more slowly. The half-life ranged from 229 days at 10 C and moisture content of 75% field capacity to 62.5 days at 40 C and 75% field capacity at pH 7.7. Additional index words. Soil moisture, soil temperature,
119 citations
TL;DR: Mars, a medium-grain cultivar that matures in 138 days, competed better with red rice than Lebonnet, a long-grain cultivation that matured in 126 days.
Abstract: Red rice (Oryza sativa L. ♯ ORYSA) densities of 5, 108, and 215 plants/m2 reduced grain yield of commercial rice (Oryza sativa L.) 22, 77, and 82%, respectively. At a cultivated rice density of 195 plants/m2, red rice at 5, 108, and 215 plants/m2 reduced straw dry weight of cultivated rice 18, 66, and 68%, respectively. At a red rice density of 5 plants/m2, reduction in number of cultivated rice grains per panicle ranged from 8 to 18%, whereas densities of 108 and 215 plants/m2 reduced grains per panicle 56 to 70%. Red rice grain yield was 24 to 33% lower in ‘Mars' rice than in ‘Lebonnet’. Mars, a medium-grain cultivar that matures in 138 days, competed better with red rice than Lebonnet, a long-grain cultivar that matures in 126 days.
119 citations
TL;DR: Corn (Zea mays L.) and soybeans were grown for 5 yr in rotation in rotation without tillage (no-till), with fall and spring Tillage (disk), and with conventional tillage(plow) in the final year of the experiment.
Abstract: Corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] were grown for 5 yr in rotation without tillage (no-till), with fall and spring tillage (disk), and with conventional tillage (plow). Weed distribution and weed yields were measured in the final year of the experiment. Grass weed yield, primarily due to green foxtail [Setaria viridis (L.) P. Beauv. #3 SETVI], was significantly higher in the no-till system. Broadleaf weed distribution and yield were similar in all tillage systems. Additional index words. No-till, reduced till, Zea mays, Glycine max, SETVI.
119 citations
TL;DR: In this paper, the degradation of chlorsulfuron was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques.
Abstract: Degradation of chlorsulfuron {2-chloro-N- (((4- methoxy- 6- methyl-1,3 ,5 -triazin-yl)amino) carbonyl) benzene- sulfonamide} in acidic and alkaline soils was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques. Soil sterilization with either ethylene oxide (EtO) or gamma irradiation significantly reduced breakdown of chlorsulfuron; the ability for degrada- tion was restored by reinoculation with indigenous soil micro- organisms. Streptomyces griseolus (a soil actinomycete), Aspergillus niger, and Penicillium sp. (soil fungi) were demon- strated to degrade 14C-chlorsulfuron in pure culture. In addition to microbial breakdown, chemical hydrolysis was an important factor in the disappearance of chlorsulfuron from soil. The contribution of chemical hydrolysis to total degradation was a function of soil pH, with hydrolysis oc- curring most rapidly in acidic soils. Both dissipation processes slowed markedly at low temperatures. Additional index words. Soil pH, soil temperature, soil mois- ture, Streptomyces griseolus, Aspergillus niger, Penicillium
110 citations
TL;DR: Growth and morphological differences were greatest between cultivars and red rice biotypes, less between blackhull and strawhull types, and least among collections withinblackhull or strawh Hull.
Abstract: Pot experiments were conducted in the field at Stuttgart, AR, during 1982 and 1983 to evaluate growth and morphological differences between strawhull and black- hull red rice (Oryza sativa L. #3 ORYSA) biotypes collected from Arkansas, Louisiana, and Texas. All red rice biotypes were compared with rice (Oryza sativa L.) cultivars 'Lebonnet' and 'Nortai'. Growth and morphological differences were greatest between cultivars and red rice biotypes, less between blackhull and strawhull types, and least among collections within blackhull or strawhull. Cultivars emerged slower, were shorter, tillered less, produced less straw and fewer panicles/plant, had a lower leaf area index, and had less grain shattering than most of the red rice biotypes. Blackhull red rice biotypes tillered 27% more, produced 18% more straw, and had later maturity than strawhull. Blackhull red rice from Arkansas emerged earlier, tillered 6 to 38% more, and produced 8 to 38% more panicles per plant than other red rice biotypes, whereas blackhull red rice from Texas was 11 to 26% taller at maturity than other biotypes. Additional index words. Strawhull red rice, blackhull red rice, ORYSA.
109 citations
TL;DR: The spatial variation of measured pesticide concentrations is often a complicating factor in interpreting the results from field studies as discussed by the authors, particularly when the study objective is quantitative evaluation of pathways of pesticide loss (leaching, degradation) or efficacy.
Abstract: The spatial variation of measured pesticide concentrations is often a complicating factor in interpreting the results from field studies. This is particularly true when the study objective is quantitative evaluation of pathways of pesticide loss (leaching, degradation) or efficacy. The variation can result from a lack of uniformity in pesticide or water application (an extrinsic factor) or from spatial differences in various physical, chemical, and biological processes (intrinsic factors) that act to transport and transform pesticides in the field. Most research attention to date has not focused on the spatial variation of these basic processes, but rather on the total spatial variation (extrinsic plus intrinsic) in the measured concentrations of residual pesticide.
TL;DR: In this article, the phytotoxicity of chlorsulfuron was compared in six soils, and the relationship of activity to soil physical and chemical properties was evaluated; the influence of soil pH (4.2 to 7.8) on phytoxicity and adsorption of chlsulfuron in- corporated into high-organic-matter soil was also studied.
Abstract: The phytotoxicity of chlorsulfuron {2-chloro- N- (((4-methoxy -6 -methyl - 1,3,5 -triazin-2-yl)amino)car- bonyl)benzenesulfonamide} was compared in six soils, and the relationship of activity to soil physical and chemical properties was evaluated. The influence of soil pH (4.2 to 7.8) on phytotoxicity and adsorption of chlorsulfuron in- corporated into high-organic-matter soil was also studied. For the phytotoxicity studies, corn (Zea mays L. 'Pioneer 3320') was used as the bioassay plant. Organic matter was the soil variable most highly correlated with chlorsulfuron phytotoxicity. There was an inverse relationship between phytotoxicity and organic matter. No significant relation- ship between clay content and chlorsulfuron toxicity was observed. The adsorption of chlorsulfuron decreased with increasing soil pH while desorption was greater at alkaline pH. Phytotoxicity of chlorsulfuron increased with increasing soil pH and reached a maximum at pH 6.9. Additional index words. Soil organic matter, soil pH, soil clay content, bioassay.
TL;DR: The seed composition in the upper 15 -cm soil horizon was determined and correlated with weed seedlings growing with fieldbeans and redroot pigweed, yellow foxtail, and barnyardgrass growing in corn fields in the fall of the year and plants growing in the field with field- beans the following year.
Abstract: The seed composition in the upper 15 -cm soil horizon was determined and correlated with weed seedlings growing with fieldbeans (Phaseolus vulgaris L. 'Valley'). The total seed reservoir averaged 250 seed/kg of soil, and 19 species were represented. Seed occurring with the most frequency were redroot pigweed (Amarantbus retroflexus L. #3 AMARE), common lambsquarters (Cbenopodium album L. # CHEAL), and common purslane (Portulaca oleracea L. # POROL). Seed from these plants accounted for over 85% of the seed found. The number of barnyard- grass (Ecbinocbloa crus-galli (L.) Beauv. # ECHCG), buffalo- bur (Solanum rostratum Dunal # SOLCU), common lambs- quarters, common purslane, and common sunflower (Heli- antbus annuus L. # HELAN) seed in the soil was correlated with the number of plants growing in the field with field- beans. A correlation occurred between redroot pigweed, yellow foxtail (Setaria lutescens (Weigel.) Hubb. # SETLU), and barnyardgrass growing in corn (Zea mays L.) fields in the fall of the year and plants growing in the field with field- beans the following year. Additional index words. Seed bank, germination, Amarantbus retroflexus, Cbenopodium album, Portulaca oleracea, AMARE, CHEAL, POROL, SOLCU, HELAN, SETLU.
TL;DR: The range of soybean leaf area reductions occasioned by proximity to individual weed species corresponded fairly well with differences in soybean yield reduction, and leaf area of soy bean was higher at greater distances from the weed for all weed species.
Abstract: Field experiments were conducted in 1979, 1980, and 1981 to determine the level of interference five broadleaf weed species exert on soybean lGlycine max (L.) Merr.l. Weed species studied were common cocklebur (Xanthium pensylvanicum Wallr. #3 XANST), common ragweed (Am- brosia artemesiifolia L. # AMBEL), common lambsquarters (Chenopodium album L. # CHEAL), sicklepod (Cassia obtusi- folia L. # CASOB), and redroot pigweed (Amaranthus retro- flexus L. # AMARE). The following soybean seed yield reductions were observed with a density of 16 weeds/10-m row: redroot pigweed 22%, common lambsquarters 15%, common ragweed 12%, and sicklepod 5%, respectively. At a density of 8 weeds/10-m row, common cocklebur reduced soybean yield 11%. No single weed growth parameter pre- dicted soybean seed yield reduction for all weed species. Soybean height was reduced by sicklepod competition; was not affected by competition from common lambsquarters, common ragweed, or common cocklebur; and was increased in the presence of redroot pigweed at 12 weeks after planting, when measured 30 cm from the weeds. Leaf area of soybean was higher at greater distances from the weed for all weed species. The range of soybean leaf area reductions occasioned by proximity to individual weed species corresponded fairly well with differences in soybean yield reduction. Additional index words. Weed competition, economic thresh- olds, Xantbium pensylvanicum, Ambrosia artemesiifolia, Chenopodium album, Cassia obtusifolia, Amaranthus retro - flexus, XANST, AMBEL, CHEAL, CASOB, AMARE.
TL;DR: Analysis of free amino acid pool sizes indicated that levels of the biosyn- thetically related amino acids leucine and valine were sub- stantially decreased in cells exposed to 10 pM herbicide, suggesting a specific interaction of this imidazolinone herbicide with leukine, valine, and iso- leucines metabolism.
Abstract: Effects of the imidazolinone herbicide AC243 997 (2 -(5-isopropyl)-5-methyl-4-oxo- 2 -imidazolin- 2-yl) nicotinic acid) on the growth of corn (Zea mays L. 'Black Mexican Sweet') cell suspension cultures were characterized. The herbicide caused half maximal growth inhibition at con- centrations in the range of 10 nM to 30 nM. Significant reductions in protein synthesis were observed following treatment of cells with 10 lM herbicide. Analysis of free amino acid pool sizes indicated that levels of the biosyn- thetically related amino acids leucine and valine were sub- stantially decreased in cells exposed to 10 pM herbicide. Supplementation of suspension culture growth media with leucine and valine plus isoleucine (1 mM each) reversed growth inhibitory effects of AC243 997 at levels ranging from 10 nM to 1 mM. The results suggest a specific interaction of this imidazolinone herbicide with leucine, valine, and iso- leucine metabolism. Additional index words. Amino acids, cell culture, corn, Zea mays.
TL;DR: The depth distribution of weed seed, their location in relation to soil aggregates, and the size distribution of soil aggregation were determined in fields that had been under continual conventional or reduced tillage for more than 12 years as discussed by the authors.
Abstract: The depth distribution of weed seed, their location in relation to soil aggregates, and the size distribution of soil aggregates were determined in fields that had been under continual conventional or reduced tillage for more than 12 years. Soil samples were taken at three depths in the spring and fall of 1982, and soil aggregates were classified into seven size classes by dry, rotary sieving. Subsamples were deflocculated and washed through sieves to recover weed seed. In the spring, 85% of all seed in the reduced- tillage and 28% of those in the conventional-tillage soil were in the 0- to 5-cm-depth layer. Conventional tillage incorpo- rated weed seed uniformly into various soil aggregate classes, whereas with reduced tillage more seed accumulated in the unaggregated fraction of the soil. In the fall, weed seed dis- tribution in relation to soil depth and among soil aggregate classes was similar for both tillage regimes. Additional index words. Seed-soil microsites, seed dormancy, seed germination, soil aggregation, soil structure, tillage.
TL;DR: Seed dormancy does not play a role in the germi- nation ecology of curly dock, and it shows that buried seeds exposed to natural seasonal temperature changes remain nondormant.
Abstract: Seed dormancy does not play a role in the germi- nation ecology of curly dock (Rumex crispus L. #3 RUMCR). This study confirms reports that freshly matured seeds are nondormant, and it shows that buried seeds exposed to natural seasonal temperature changes remain nondormant.
TL;DR: In this paper, field studies were conducted for 4 yr with HOE- 39866 (ammonium- (3 -amino-3 -carboxypropyl) -methyl- phosphinatel and for 2 yr with SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) to compare foliar activities with those of paraquat (1,1 '-dimethyl-4,4'-bi-pyridinium ion) and glyphosate (N-(phosphoneomet
Abstract: Field studies were conducted for 4 yr with HOE- 39866 (ammonium- (3 -amino-3 -carboxypropyl) -methyl- phosphinatel and for 2 yr with SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) to compare foliar activities with those of paraquat (1,1 '-dimethyl-4,4'-bi- pyridinium ion) and glyphosate (N-(phosphonomethyl)gly- cine) in no-till corn (Zea mays L. 'Pioneer 3320' in 1981 and 'Pioneer 3184' in 1982 and 1983). Rates evaluated were 0.6 to 1.7 kg ai/ha for all herbicides except paraquat which was included at 0.3 and 0.6 kg ai/ha. Control of rye (Secale cereale L.) was excellent at all rates with SC-0224, paraquat, and glyphosate, but HOE- 39866 was effective only when combined with residual herbicides. All four herbicides pro- vided good initial control of horseweed (Conyza canadensis (L.) Cronq., #3 ERICA), but recovery following paraquat application was extensive. Combinations of HOE- 39866, SC-0224, and glyphosate at 0.6 kg/ha with atrazine (2- chloro- 4-(ethylamino) -6- (isopropylamino)-s-triazine) at 1.1 to 1.7 kg ai/ha + metolachlor (2-chloro-N-(2-ethyl-6- methylphenyl) -N-(2 -methoxy- 1-methylethyl)acetamide) at 1.7 kg ai/ha produced antagonistic responses against rye and sometimes horseweed. In 1983, the combination of SC-0224 + residual herbicides provided significantly better control of rye and horseweed 8 days after treatment than
TL;DR: The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and 14C-radiolabelled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] following foliar applications to purple nutsedge (Cyperus rotundus L. ♯ CYPRO) were evaluated as mentioned in this paper.
Abstract: The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and 14C-radiolabeled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] following foliar applications to purple nutsedge (Cyperus rotundus L. ♯ CYPRO) were evaluated. Salts of the monovalent cations NH4 +, K+, and Na+ and to a lesser degree the anion PO4 generally resulted in increased toxicity of these herbicides. Salts of the divalent and trivalent cations Zn++ and Fe+++ frequently reduced the activity of glyphosate and MSMA, whereas salts of the divalent Ca++ ion caused little or no effect on activity. Salts of the anions Cl–, NO3 –, CO3 —-, and SO4 – resulted in increased, decreased, or unchanged glyphosate toxicity as influenced by the associated cation. Translocation of the radiolabel of 14C-glyphosate and 14C-MSMA was increased by the addition of NH4Cl, while retention of the radiolabel within the tissue of the treated area was increased by the addition of FeCl3 to the treated leaf surface.
TL;DR: Metribuzin was much more mobile than atrazine in a leaching study and was probably adsorbed at the hydrophilic sites on the soil surfaces that were measured by EGME.
Abstract: The effect of various soil parameters on metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] efficacy was studied on seven soils and metribuzin adsorption was investigated in nine soils. Soil organic-matter and clay contents were correlated with metribuzin activity. Specific surface area, as measured by ethylene glycol monoethyl ether (EGME) was highly correlated with metribuzin activity. Soil organic-matter content and EGME surface area measurements were also highly correlated with metribuzin adsorption in soils. Since metribuzin is highly water soluble (water solubility greater than 1000 ppm), it was probably adsorbed at the hydrophilic sites on the soil surfaces that were measured by EGME. Metribuzin was much more mobile than atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] in a leaching study.
TL;DR: Canopy re- flectance data were more directly related to photographic differences in weed-crop images than were single leaf or inflorescence reflectance data, indicating that color infrared (CIR) aerial photography may be useful to detect weed populations in crops.
Abstract: Plant canopy reflectance over the 0.45- to 1.25- gm wavelength (WL) of weed species and crops was recorded with a field spectroradiometer to evaluate the possible use of remote sensing to distingu'ish weeds from crops. Weed and weed-crop species reflectance differences were gener- ally greater at the 0.85 gm WL in the near-infrared spectral region than at the 0.55 ,um WL in the visible region, indi- cating that color infrared (CIR) aerial photography may be useful to detect weed populations in crops. Canopy re- flectance data were more directly related to photographic differences in weed-crop images than were single leaf or inflorescence reflectance data. Aerial photography at altitudes of 610 to 3050 m distinguished climbing milkweed (Sarcostemma cyanchoides #3 SAZCY) in orange (Citrus sinensis (L.) Osbeck. 'Valencia') trees; ragweed parthenium (Parthenium hysteropborus L. # PTNHY) in carrot (Daucus
TL;DR: Common cocklebur (Xantbium pensylvanicum Wallr), velvedeaf (Abutilon theopbrasti Medic), and jimsonweed (Datura stramonium L. # DATST) are weeds that grow taller than soybeans and compete for limited resources such as light.
Abstract: Common cocklebur (Xantbium pensylvanicum Wallr. #3 XANPE), velvedeaf (Abutilon theopbrasti Medic. # ABUTH), and jimsonweed (Datura stramonium L. # DATST) are weeds that grow taller than soybeans (Glycine max (L.) Merr.) and compete for limited resources such as light. These weeds have an average area of influence of 0.5 mi2, thus a density of 1 to 2 plants/m2 forms a full canopy of weed leaves above the soybeans that intercept 44 to 56% of the sunlight. Shade of 44 to 56% without weeds, placed above soybeans late in the season corresponding to times of weed shading, reduced soybean yield 19 to 26%. Since reported soybean yield reductions at weed densities of 0.7 to 2.5 plants/M2 were 18 to 54% for common cocklebur and 12 to 31% for jimsonweed and velvetleaf, it was con- cluded that most of the interference from jimsonweed and velvetleaf infestations in soybeans could be ascribed to com- petition for light, but only about one-half the interference was due to competition for light for common cocklebur. Soybean photosynthesis in the field was reduced about twice as much as soybean yield at equivalent levels of shading. Additional index words. Xanthium pensylvanicum, Datura stramonium, Abutilon theopbrasti, interference, photosyn- thesis, shade, XANPE, DATST, ABUTH.
TL;DR: The results suggest that FMC 57020 blocks both diterpene and tetraterpene synthesis, suggesting that phytol levels are also reduced by the herbicide.
Abstract: The effect of FMC 57020 [2(2 chlorophenyl) methyl-4,4dimethyl-3-isoxalidinoneI on chloroplast development was examined in the cotyledons of 5-day-old, etiolated pitted morningglory (Ipomoea lacunosa L. #3 IPOLA) seedlings grown from seeds inbibed for 24 h in water or 0.5 mM FMC 57020. In etiolated tissues, protochlorophyllide content was unaffected by FMC 57020; however, the herbicide eliminated carotenoid accumulation. There was no effect of FMC 57020 on phytoene or phytofluene content, although norflurazon [4chloro -5(methylamino)-2(3-trifluoromethyl) phenyl)3(2H)-pyridazinoneJ increased phytoene content in these tissues. The Shibata shift was greatly retarded in FMC 57020-treated cotyledons, suggesting that phytol levels are also reduced by the herbicide. There were no ultrastructural effects on etioplasts; however, under low white light (150 ME*m2s l PAR), plastids of FMC 57020-treated seedlings did not develop into chloroplasts but rapidly developed ultrastructural symptoms of photobleaching. Starch was not mobilized in herbicide-treated plastids and sugar levels were higher in these plastids than in control plastids. Etiolated hypocotyl growth was inhibited by FMC 57020, whereas norflurazon had no effect upon it. Our results suggest that FMC 57020 blocks both diterpene and tetraterpene synthesis. Additional index words. Carotenoids, bleaching herbicides, terpenoids, IPOLA.
TL;DR: Canada thistle (Cirsium arvense) root samples were collected at monthly intervals over a 2-yr period from two locations to determine seasonal fluctuations in the presence and growth potential of root buds.
Abstract: Canada thistle (Cirsium arvense (L.) Scop. #3 CIRARI root samples were collected at monthly intervals over a 2-yr period from two locations to determine seasonal fluctuations in the presence and growth potential of root buds. Root bud growth was highest during late fall and winter months following death of the aerial shoots. Root fragments incubated at a constant 15 C for 2 weeks in continuous light consistently had more buds than nonincubated roots, which indicated active bud differentiation during the in- cubation period. Incubated roots produced 3 to 9 cm of new shoot length/cm root length. There were no obvious seasonal patterns in the presence of root buds or their ability to elongate at different times of the year. Carbohydrate reserves were stored preferentially in roots rather than in developing root buds or the bases of shoots. These reserves ranged from as low as 3% of root fresh weight during spring months to as high as 26% in late fall months, although the levels did not increase consistently during summer months over the locations and years of this study.
TL;DR: Interference from tumble pigweed did not significantly affect cotton fiber length, uniformity, strength, or micronaire of hand-harvested bolls, and competition, fiber quality, lint yield, crop height, AMAAL.
Abstract: Relationships between production of cotton (Gossypium birsutum L 'Westburn M') and full-season interference from tumble pigweed (Amaranthus albus L #3 AMAAL) at densities ranging from 0 to 64 plants/10 m of row were measured in three replicated experiments in the field Dry weight of harvested tumble pigweed increased by 0149 to 0402 kg/plot for each additional weed/10 m of row Intraspecific competition among tumble pigweed plants was observed at the higher weed densities Cotton plant height was reduced in all three experiments at the 32 or 64 weed densities, but harvesting difficulties were not encountered in these studies The threshold density where initial lint yield reductions occurred ranged from 4 to 16 tumble pigweed plants/10 m of row in the three experiments Lint yields were reduced from 8 to 11 kg/ha for each additional tumble pigweed plant/10 m of row Interference from tumble pigweed did not significantly affect cotton fiber length, uniformity, strength, or micronaire of hand-harvested bolls Additional index words Competition, fiber quality, lint yield, crop height, AMAAL