Showing papers in "Weed Science in 1992"
TL;DR: Information regarding the critical period of weed control in corn may lead to less reliance on the use of residual herbicides and to more reliance on well-timed postemergence herbicides, and timing of cover crop seeding and cultivations could be improved based upon critical period information.
Abstract: Field studies were conducted in southern Ontario to determine the critical period of weed control in grain corn and the influence of weed interference on corn leaf area. The Gompertz and logistic equations were fitted to data representing increasing durations of weed control and weed interference, respectively. The beginning of the critical period varied from the 3- to 14-leaf stages of corn development However, the end of the critical period was less variable and ended on average at the 14-leaf stage. Weed interference reduced corn leaf area by reducing the expanded leaf area of each individual leaf and accelerating senescence of lower leaves. In addition, weed interference up to the 14-leaf stage of corn development impeded leaf expansion and emergence in 1989.
437 citations
TL;DR: The effect of different levels of tillage and weed management on population, distribution, and germination of weed seed was evaluated in three tillage systems at Arlington and Hancock, WI, in 1989 and 1990 and seed numbers with no-tillage and Weed-free conditions decreased by 40% relative to herbicide alone.
Abstract: The effect of different levels of tillage and weed management on population, distribution, and germination of weed seed was evaluated in three tillage systems at Arlington and Hancock, WI, in 1989 and 1990. Over 60% of all weed seed in the top 19 cm of soil were found in the top 1 cm in no-tillage at both sites. As depth increased, concentration of weed seed declined logarithmically in no-tillage. In chisel plowing, over 30% of seed were in the top 1 cm and seed concentration decreased linearly with depth. Moldboard plowing had uniform distribution of weed seed in the top 19 cm of soil. Preemergence metolachlor plus atrazine decreased weed seed population by 50% compared with no treatment over all tillage systems. One year of the herbicide treatment plus handweeding to assure weed-free conditions did not reduce seed numbers in chisel plowing or moldboard plowing compared to herbicide alone. Seed numbers with no-tillage and weed-free conditions decreased by 40% relative to herbicide alone. Common lambsquarters germination was 40% greater in moldboard plowing and chisel plowing compared with no-tillage. Germination was highest in seed taken from 9 to 19 cm deep in moldboard plowing and from 0 to 9 cm deep in chisel plowing.
285 citations
TL;DR: A simple model was developed to validate the observation that rate of change in the weed seedbank is influenced by type of tillage and weed control effectiveness, and showed that seedbank decline was generally more rapid after moldboard plowing.
Abstract: Changes in the weed seedbank due to crop production practices are an important determinant of subsequent weed problems. Research was conducted to evaluate effects of primary tillage (moldboard plowing and chisel plowing), secondary tillage (row cultivation), and herbicides on weed species changes in the soil seedbank in three irrigated row crop rotational sequences over a 3-yr period. The cropping sequences consisted of continuous corn for 3 yr, continuous pinto beans for 3 yr, or sugarbeets for 2 yr followed by corn in the third year. Cropping sequence was the most dominant factor in- fluencing species composition in the seedbank. This was partly due to herbicide use in each cropping sequence producing a shift in the weed seedbank in favor of species less susceptible to applied herbicides. A comparison between moldboard and chisel plowing indicated that weed seed of predominant species were more prevalent near the soil surface after chisel plowing. The number of predominant annual weed seed over the 3-yr period increased more rapidly in the seedbank after chisel plowing compared to moldboard plowing unless effective weed control could be maintained to produce a decline in seedbank number. In this case, seedbank decline was generally more rapid after moldboard plowing. Row cultivation generally reduced seedbanks of most species compared to uncultivated plots in the pinto bean and sugarbeet sequences. A simple model was developed to validate the observation that rate of change in the weed seedbank is influenced by type of tillage and weed control effectiveness. Nomenclature: Corn, Zea mays L.; pinto beans, Phaseolus vulgaris L.; sugarbeets, Beta vulgaris L. Additional index words: Weed shifts, reduced tillage, conservation tillage, population dynamics, modeling, KCHSC, AMARE, CHEAL, SOLSA, SETVI, ERACN.
242 citations
TL;DR: Seedbanks and seedling emergence of annual weeds were examined in arable fields at eight locations in the Corn Belt and can be employed by bioeconomic weed management models, which currently use coarse estimates of emergence percentages to customize recommendations for weed control.
Abstract: Seedbanks and seedling emergence of annual weeds were examined in arable fields at eight locations in the Corn Belt. Seed densities were estimated by direct seed extraction from each of several soil cores in each sampled plot. Average total seedbank densities ranged from 600 to 162 000 viable seed m-2 among locations. Coefficients of variation (CV) typically exceeded 50%. CV for seed densities of individual species usually exceeded 100%, indicating strongly aggregated distributions. CV were lower for species with dense seed populations than those with sparse seed populations. Variance of total seedbank densities was unstable when < 10 cores were examined per plot, but stabilized at all locations when ≥ 15 cores were analyzed, despite a 12-fold difference in plot size and 270-fold difference in seed density among locations. Percentage viable seed that emerged as seedlings in field plots ranged from < 1% for yellow rocket to 30% for giant foxtail. Redroot pigweed and common lambsquarters were the most frequently encountered species. Emergence percentages of these species were related inversely to rainfall or air temperatures in April or May, presumably because anoxia and/or high temperatures induced secondary dormancy in nondormant seed. From 50 to 90% of total seed in the seedbank were dead. This information can be employed by bioeconomic weed management models, which currently use coarse estimates of emergence percentages to customize recommendations for weed control.
184 citations
TL;DR: The DNA sequence variation among the R and S kochia biotypes was used to characterize six Ada County, Idaho, kochIA collections for correlation between phenotypic chlorsulfu- ron susceptibility and restriction digest patterns (RFLPs) of polymerase chain reaction amplification products.
Abstract: The DNA sequence of a 196 base pair (bp) region of the acetolactate synthase (ALS) genes of three weed species, kochia, prickly lettuce, and Russian thistle, was determined. This region encompasses the coding sequence for Domain A, a region of the amino acid sequence previously demonstrated to play a pivotal role in conferring resistance to herbicides that inhibit ALS. The Domain A DNA sequence from a chlorsulfuron-resistant (R) prickly lettuce biotype from Idaho differed from that of a chlorsulfuron-susceptible (S) biotype by a single point mutation, which substituted a histidine for a proline. The Domain A DNA sequence from an R kochia biotype from Kansas also differed from that of an S biotype by a single point mutation in the same proline codon. This point mutation, however, conferred substitution of threonine for proline. Two different ALS-homologous sequences were isolated from an R biotype of Russian thistle. Neither sequence encoded amino acid substitutions in Domain A that differed from the consensus S sequence. The DNA sequence variation among the R and S kochia biotypes was used to characterize six Ada County, Idaho, kochia collections for correlation between phenotypic chlorsulfu- ron susceptibility and restriction digest patterns (RFLPs) of polymerase chain reaction amplification products. Most collections showed excellent correspondence between the RFLP patterns and the phenotypic response to chlorsulfu- ron application. However, one entirely R collection had the RFLP pattern of the S biotype, suggesting that resistance was not due to mutation in the proline codon. Nomenclature: Chlorsulfuron, 2-chloro-N-(((4-methoxy- 6 -methyl-1,3,5-triazin-2-yl)amino) carbonyl)benzenesulfonamide; acetolactate synthase (ALS; EC 4.1.3.18); kochia, Kochia scoparia L. (Schrad.) #3 KCHSC; prickly lettuce Lactuca serriola L. # LACSE; Russian thistle, Salsola iberica, Sennen and Pau # SASKR.
154 citations
TL;DR: In a field research conducted at Hancock, Wisconsin, from 1985 through 1987 to evaluate the effects of various tillage systems on population dynamics and control of annual weed species in corn grown continuously on a loamy sand soil without irrigation as mentioned in this paper, the authors found that green foxtail densities were greater in chisel plow and no-tillage than in the conventional tillage system, while ridge tillage had densities lower than all other tillage.
Abstract: Field research was conducted at Hancock, WI, from 1985 through 1987 to evaluate effects of conven- tional tillage, chisel plow, ridge tillage, and no-tillage systems on population dynamics and control of annual weed species in corn grown continuously on a loamy sand soil without irrigation In all years of the study, green foxtail densities were greater in chisel plow and no-tillage than in the conventional tillage system, while ridge tillage had densities lower than all other tillage systems Common lambsquarters density in the chisel plow system reached nearly 500 plants m-2 compared to less than 75 plants m-2 in the other tillage systems when averaged over years Average redroot pigweed densities in the no- tillage and chisel plow systems were 307 and 245 plants m-2 compared to less than 25 plants m-2 in the conventional and ridge tillage systems Horseweed was observed only in no-tillage and ridge tillage plots Green foxtail and redroot pigweed were more difficult to control in chisel plow and no-tillage than in the conventional and ridge tillage systems with several herbicide treatments Corn yields were not affected by tillage systems under weed-free conditions Corn yield differences among tillage systems when the same herbicide treatment was applied appeared to be due to differences in weed control Nomenclature: Common lambsquarters, Chenopodium al- bum L #3 CHEAL; green foxtail, Setaria viridis (L) Beauv # SETVI; horseweed, Conyza canadensis (L) Cronq # ERICA; redroot pigweed, Amaranthus retroflexus L # AMARE; corn, Zea mays L 'Hughes 5302' Additional index words Alachlor, atrazine, conservation tillage, cyanazine, metolachlor, no-tillage, AMARE, CHEAL, ERICA, SETVI
144 citations
TL;DR: Corn yields showed weed management levels above minimum control are not justified regardless of tillage and crop rotation, and giant foxtail stands were reduced following wheat in no- tilling, probably because of the allelopathic influence of wheat straw.
Abstract: A long-term integrated pest management study initiated in 1980 and continued through 1991 was conducted to determine interactions of tillage, crop rotation, and herbicide use levels on weed seed popula- tions, weed populations, and crop yield. This paper presents giant foxtail seed population and stand along with corn yield in continuous corn, corn rotated with soybean, or corn following wheat in a soybean-wheat-corn rotation. Increasing herbicide use levels above the minimum reduced giant foxtail seed in the 0- to 2.5-cm depth of soil. Reducing tillage from conventional moldboard plowing to chiseling to no-tilling increased giant foxtail seed in only the top 0 to 2.5 cm of soil. No- tilling increased giant foxtail seed over conventional tillage in each year data were collected. Growing corn in a soybean-corn or soybean-wheat-corn rotation reduced giant foxtail seed from corn grown continuously in all three soil depths sampled: 0 to 2.5 cm, 2.5 to 10 cm, and 10 to 20 cm. Although stands of giant foxtail tended to follow soil weed seed counts, crop rotation significantly reduced giant foxtail stand with maximum reduction in the soybean-wheat-corn rotation in all tillage systems. Giant foxtail stands were reduced following wheat in no- tilling, probably because of the allelopathic influence of wheat straw. Corn yields showed weed management levels above minimum control are not justified regardless of tillage and crop rotation. Nomenclature: Giant foxtail, Setaria faberi; Herrm. #3 SETFA; corn, Zea mays L., 'Callahan 766'; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.
137 citations
TL;DR: Hairy beggarticks seed can germinate under both a 12-h photoperiod and a 24-h dark regime, andRadicle growth was more sensitive to extreme pH than germination, and germination decreased above or below this range.
Abstract: Effects of environmental factors on germination and emergence of hairy beggarticks were examined in laboratory and greenhouse studies. Optimum temperature range for germination of hairy beggarticks was 25/20 to 35/30 C (day/night, 12/12 h). Germination decreased above or below this range. Temperatures below 15/10 C and above 45/40 C were unfavorable for germination. Hairy beggarticks seed can germinate under both a 12-h photoperiod and a 24-h dark regime. Seed germinated 78 to 90% in buffer solutions of pH 4 to 9. Radicle growth was more sensitive to extreme pH than germination. Osmotic stress up to −0.1 MPa had little effect on germination, but less than 3% of the seed germinated at an osmotic stress of −0.75 MPa. Hairy beggarticks seed (13%) germinated at NaCl concentration of 100 mM but failed to germinate at 200 mM NaCl. Maximum emergence occurred when seed were planted less than 1 cm deep. No seedlings emerged when planted 10 cm deep. Flooding even for a day following planting decreased emergence to 25% compared to no flooding (56%). Seedling emergence decreased sharply with a further increase in duration of flooding, and no seedlings emerged when flooding was maintained up to 28 d after planting.
118 citations
TL;DR: Spatial distribution of broadleaf weeds within 14 North Carolina soybean filelds was characterized by fitting negative binomial distributions to frequency distri- butions of weed counts in each field, indicating a high degree of patchiness and that the population as a whole was patchy.
Abstract: Spatial distribution of broadleaf weeds within 14 North Carolina soybean filelds was characterized by fitting negative binomial distributions to frequency distri- butions of weed counts in each field. In most cases, the data could be represented by a negative binomial distribution. Estimated values of the parameter K of this distribution were small, often less than one, indicating a high degree of patchiness. The data also indicated that the population as a whole was patchy. Counts of individual species were positively correlated with each other in some fields and total weed count could be represented by a negative binomial for 12 of the 14 fields. Nomenclature: Soybean, Glycine max (L.) Merr. Additional index words. Weed patchiness, weed spatial distribution, negative binomial, spatial dispersion.
114 citations
TL;DR: Contour graphs were developed that predicted imazetha- pyr rates required for various levels of weed control based upon weed leaf number at application and demonstrate how control data can be used for developing effective reduced-rate herbicide recommendations based on Weed leaf number.
Abstract: Field experiments were conducted in 1986, 1987, and 1988 to evaluate imazethapyr rate and time of application on postemergence control of 24 weed species. Contour graphs were developed that predicted imazetha- pyr rates required for various levels of weed control based upon weed leaf number at application. Rates below the labeled rate (70 g ha7l) provided 90% or greater control of common cocklebur, smallflower morningglory, and smooth pigweed if applied to 3 true-leaf or smaller weeds and of barnyardgrass, seedling johnsongrass, and Palmer amaranth if applied while weeds were in the cotyledon or 1 true-leaf stage. A rate of 70 g ha-l provided 90% control of large crabgrass in the 1 true-leaf stage. Entireleaf morningglory, red rice, pitted morningglory, and velvetleaf are not susceptible enough to imazethapyr for 90% or greater control to be obtained with rates lower than 70 g ha-1 at the 1 true-leaf growth stage. These data demonstrate how control data can be used for developing effective reduced-rate herbicide recommendations based on weed leaf number. Nomenclature: Imazethapyr, (?)- 2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-lH-im- idazol-2-yl)-5-ethyl-pyridinecarboxylic acid; barnyard- grass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; common cocklebur, Xanthium strumarium L. # XANST; entireleaf morningglory, Ipomoea hederacea var. integrius- cula Gray # IPOHG; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri S.Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; red rice, Oryza sativa L. # ORYSA; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. # IAQTA; smooth pigweed, Amaranthus hybridus L. # AMACH; velvetleaf, Abutilon theophrasti Medik. # ABUTH. Additional index words. Contour graphs, reduced rates, time of application, ABUTH, AESVI, AMACH, AMAPA, AMATU, ANVCR, CASOB, CLYMU, CRIHA, DATST, DIGSA, ECHCG, IAQTA, IPOHG, IPOLA, IPOWR, ORYSA, PHBPU, SEBEX, SETFA, SIDSP, SORHA, ELEIN, XANST.
113 citations
TL;DR: The empirical model describing the relationship between relative leaf area of the weeds shortly after crop emergence and yield loss appeared to have several advantages for management applications, whereas the mechanistic model is more suited for research purposes.
Abstract: The performance of a mechanistic simulation model of crop-weed competition was evaluated with data on the effects of weed density, relative time of weed emergence, and environmental conditions on crop yield for three different crop-weed combinations. Reductions in crop yields due to weed competition were simulated accurately for all experiments, except for one case in which severe water stress combined with weed competi- tion altered crop morphological development (height and leaf area). The mechanistic model was then used to assess the potential and constraints of two empirical models of crop-weed competition, one based upon weed density and relative time of emergence, and the other on relative leaf area. The empirical model describing the relationship between relative leaf area of the weeds shortly after crop emergence and yield loss appeared to have several advantages for management applications, whereas the mechanistic model is more suited for research purposes. Additional index words. Simulation, interference, Zea mays L., Echinochloa crus-galli (L.) Beauv. #3 ECHCG, Beta vulgaris L., Chenopodium album L. #3 CHEAL, Lycopersi- con esculentum L., Solanum ptycanthum Dun. #3 SOLPT.
TL;DR: Observed segregation of phenotypes in F2 and testcross populations conformed to segregation ratios predicted for a trait with inheritance controlled by a single partially dominant nuclear gene.
Abstract: A diclofop-methyl-resistant biotype of Italian ryegrass was characterized to determine the expression and inheritance of herbicide resistance and whether this trait was due to the presence of a diclofop-insensitive form of acetyl-coenzyme A carboxylase (ACCase). At the whole plant level, the resistant biotype was > 93-fold more resistant to diclofop-methyl than the susceptible biotype. Crosses of diclofop-resistant and -susceptible plants were performed to produce Fl plants. No maternal effects were evident in responses of reciprocal Fl plants to diclofop. GRSO diclofop rates determined for resistant, Fl, and susceptible plants were 15, 6.3, and 0.16 kg ha-1, respectively. F2 populations treated with a 7.5 kg ha-1 rate of diclofop exhibited three injury response pheno- types 3 wk after treatment: a susceptible (S) phenotype which was killed, an intermediate resistance (I) phenotype with severe injury, and a resistant (R) phenotype with little or no injury. Testcross progeny exhibited only I and S phenotypes. Observed segregation of phenotypes in F2 and testcross populations conformed to segregation ratios predicted for a trait with inheritance controlled by a single partially dominant nuclear gene. ACCase activity determined in crude cell-free extracts of resistant, Fl, and susceptible biotypes exhibited ISO values of 50, 20, and 0.7 FiM diclofop, respectively. A positive relationship between
TL;DR: In this article, the performance of a mechanistic simulation model of crop-weed competition was tested with data on the critical period of weed competition in sugarbeets and both seeded and transplanted tomatoes.
Abstract: The performance of a mechanistic simulation model of crop-weed competition was tested with data on the critical period of weed competition in sugarbeets and both seeded and transplanted tomatoes. In general, there was good agreement between simulated and observed yields for different periods of weed interference in each crop. The model was then used to evaluate the influence of weed density, weed height, and weather conditions on timing of the critical period. Simulations suggested that the greater the weed density, the shorter the period of time that the crop could tolerate early-season competition, and the longer the period of time that the crop must be kept weed free to prevent yield losses. Simulations also suggested that the length of time that a crop can tolerate early-season weed competition is related more to the availability of soil moisture, or possibly essential nutrients, than to light limitations.
TL;DR: Effects of tillage and herbicide application method on the persistence and residual activity of clomazone, imazaquin, and imazethapyr were investigated in a 2-yr field study.
Abstract: Effects of tillage and herbicide application method on the persistence and residual activity of clomazone, imazaquin, and imazethapyr were investigated in a 2-yr field study. Herbicides were applied preemer- gence and preplant incorporated to conventional- and reduced-tillage soybeans in 1987 and 1988. Herbicide dissipation was monitored using chromatographic and bioassay techniques. In 1987, dissipation rates for cloma- zone, imazaquin, and imazethapyr were similar, regard- less of tillage system or application method. In 1988, all three herbicides applied preplant incorporated dissipated more slowly than in preemergence treatments. Corn planted in rotation in 1989 displayed greater levels of injury in the incorporated treatments for all three herbicides. Although herbicide concentrations were simi- lar 322 d following application in both tillage treatments in 1989, corn ijUury was greater with imazaquin and isazethapyr and less with clomazone in the reduced- tillage plots than in the conventional-tillage treatments. Nomenclature: Clomazone, 2-((2-chlorophenyl)methyl)- 4,4-dimethyl-3-isoxazolidinone; imazaquin, 2-(4,5-di- hydro-4-methyl-4-(1-methylethyl)-5-oxo-lH-imidazol-2- yl)-3-quinolinecarboxylic acid; imazethapyr, (?)-2-(4,5- dihydro-4-methyl-4-(1-methylethyl)-5-oxo-lH-imidazol-2- yl)-5-ethyl-3-pyridinecarboxylic acid; corn, Zea mays L. 'Pioneer 3377'. Additional index words. Herbicide dissipation, bioassay, reduced tillage, no-till.
TL;DR: Growth and development of red rice (strawhull) and 'Lemont' and 'Newbonnet' rice were compared in 1987 and 1988 under noncompetitive field conditions at Stuttgart, AR as discussed by the authors.
Abstract: Growth and development of red rice (strawhull) and 'Lemont' and 'Newbonnet' rice were compared in 1987 and 1988 under noncompetitive field conditions at Stuttgart, AR. Growth and developmental differences were greater between red rice and rice than between rice cultivars. Compared to rice, red rice was taller, produced more culms m-2 and aboveground dry weight, had higher leaf area indices, and had a greater flag leaf area. Also, it had lower leaf to stem ratios late in the season, had greater crop growth rate early in the season but less late in the season, and produced a lower grain weight than rice. Compared to Newbonnet, Lemont plants were shorter at 60 d after emergence or later, produced more culms mn2, had a greater leaf area index, and produced higher grain weight than Newbonnet. Also, Lemont and Newbonnet produced comparable leaf to stem ratios, crop growth rates, and flag leaf areas. Nomenclature: Red rice, Oryza sativa L. #3, 'strawhull'; rice Oryza sativa L.
TL;DR: In this paper, the photolytic degradation of several imidazolinone herbicides in solution and on soil was investigated, and it was shown that ultraviolet light caused 100% degradation of imazaquin, imazethapyr, and imazapyr.
Abstract: The photolytic degradation of several imidazolinone herbicides in solution and on soil was investigated. Ultraviolet light caused 100% degradation of imazaquin, imazethapyr, and imazapyr, and 87 and 8% degradation of imazamethabenz and atrazine in aqueous solutions, respectively, after 48 h. The order of susceptibility to photolysis in decreasing order was imazaquin = imazethapyr > imazapyr > imazamethabenz > atrazine. In soil Studies, 45% of imazaquin and 52% of imazethapyr dissipated from moist sand after 48 h of exposure. Herbicide dissipation on air-dry sand and on field capacity and air-dry silty clay loam was less than 10% in most instances. Atrazine photolysis was not detected. This research indicates that photolysis of imidazolinone herbicides in solution is rapid. Photolysis on soil occurs readily on coarse-textured wet soils probably due to greater availability of the herbicide for photochemical alteration.
TL;DR: Avena sterilis ssp. ludoviciana was found to have high levels of resistance to a range of aryloxyphenoxypropionate and cyclohexanedione graminicides in a wild oat population from Western Australia.
Abstract: Resistance to the methyl ester of diclofop, an aryloxyphenoxypropionate graminicide, was shown for a wild oat (Avena fatua) population from Western Australia, and marked resistance to a range of aryloxyphenoxypropionate and cyclohexanedione graminicides was detected in a winter wild oat (Avena sterilis ssp. ludoviciana) population from South Australia. The A. sterilis biotype exhibited high levels of resistance to the aryloxyphenoxypropionate herbicides diclofop, fluazifop, haloxyfop, fenoxaprop, quizalofop, propaquizafop, and quinfurop and low levels of resistance to the cyclohexanedione herbicides sethoxydim, tralkoxydim, and cycloxydim. Ratios of LD50 values for responses of resistant and susceptible A. sterilis to the aryloxyphenoxypropionate herbicides were between 20 for propaquizafop and > 1,000 for fluazifop, and were between 2.5 and 3 for the cyclohexanedione herbicides. The LD50 value for diclofop for the A. fatua biotype was 442 g ai ha-1 which was 2.7-fold that of a susceptible control. Thirty-three percent of the plants survived at the registered rate of application.
TL;DR: Greene et al. as discussed by the authors found that common and Drummond golden weed plants had a yellow image on conventional color (0.40- to 0.70-am) aerial photographs that made them distinguishable from associated plants and soil.
Abstract: Common and Drummond goldenweed are troublesome subshrubs that often invade rangelands in southern Texas. Both species produce a profusion of conspicuous golden-yellow flowers in the fall. Common goldenweed flowers from late September to mid-October, whereas Drummond goldenweed flowers from mid- November to early December. Plant canopy reflectance measurements made on both species showed that they had higher visible (0.63- to 0.69-gm waveband) reflectance than did associated plant species and bare soil during flowering. Flowering common and Drummond golden- weed plants had a yellow image on conventional color (0.40- to 0.70-am) aerial photographs that made them distinguishable from associated plants and soil. Computer analyses of the conventional color film transparencies showed that common and Drummond goldenweed infesta- tions could be quantified from associated vegetation and soil. Flowering common goldenweed plants could also be detected on conventional color aerial video imagery. Nomenclature: Common goldenweed, Isocoma coronopifo- lia (Gray) Greene #3 IOCCO; Drummond goldenweed, Isocoma drummondii (T.&G.) Greene, # HAPDR. Additional index words. Reflectance, conventional color photography, color-infrared photography, conventional color video imagery, rangelands, IOCCO, HAPDR.
TL;DR: Data on distribution of broadleaf weeds in 14 soybean fields was used in simulation experiments to investigate the potential for improving decision making with information about weed patchiness and the cost of assuming a regular distribution when making POST decisions was found to be low.
Abstract: Broadleaf weeds apparently have patchy distri- butions within a field while POST control decisions are made assuming a regular spatial distribution. As a result, yield loss from weed competition may be overestimated, possibly leading to mistakes in choosing the optimal control treatment. Data on distribution of broadleaf weeds in 14 soybean fields were used in simulation experiments to investigate the potential for improving decision making with information about weed patchiness. The feasibility of modeling weed distribution in individual fields was also examined. Overall, the cost of assuming a regular distribution when making POST decisions was found to be low. Errors that occurred most often involved recommending more intensive control than was actually required, although in a few cases less intensive control was recommended. Error in the yield loss estimated for the uncontrolled population did not indicate the potential for a mistake in decision making for a field. Accurately modeling distribution of weeds within fields may be difficult as a result of correlations between distributions of individual species within a field and variation in distributions between fields. Nomenclature: Soybean, Glycine max (L.) Merr. Additional index words. Simulation, decision models, weed management, weed competition, Glycine max.
TL;DR: The response of 'C-20' navy bean and 'Franken- muth' soft white winter wheat grown in rotation to clomazone, imazethapyr, bentazon, and acifluorfen was examined and seed moisture at harvest and yield was not reduced compared to the weed-free control.
Abstract: The response of 'C-20' navy bean and 'Franken- muth' soft white winter wheat grown in rotation to clomazone, imazethapyr, bentazon, and acifluorfen was examined. Clomazone at 560 and 430 g ai ha-1 plus 800 g ai ha71 pendimethalin and 2000 g ai ha-1 chloramben visibly injured navy bean in 1 of 2 yr. However, navy bean seed moisture at harvest and yield was not reduced compared to the weed-free control. PPI and PRE treatments of 70 g ai ha-1 imazethapyr did not injure navy bean or reduce yield. Imazethapyr applied POST at 70 g ha-l plus nonionic surfactant visibly injured navy bean. The addition of urea ammonium nitrate to imazethapyr enhanced visible injury and seed moisture compared to nonionic surfactant alone in 1 of 2 yr. However, seed yield was not reduced. Seed moisture at harvest was greater following treatment with 430 g ai ha-1 acifluorfen plus nonionic surfactant or urea ammonium nitrate and 140 and 280 g ha1 acifluorfen plus 840 g ai ha-1 bentazon in 1 of 2 yr compared to the weed-free control, but yield was not reduced. Wheat yield was reduced in 2 of 2 and 1 of 2 yr by 560 g ha-1 and 430 g ha-1 clomazone, respectively, plus pendimethalin plus chloramben compared to the weed-free control. Wheat yield was not reduced by imazethapyr, bentazon, or acifluorfen. Nomenclature: Acifluorfen, 5-(2-chloro-4- (trifluoromethyl)phenoxy)-2-nitrobenzoic acid; bentazon, 3-(1-methylethyl)-(lH)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; chloramben, 3-amino-2,5-dichlorobenzoic acid; clomazone, 2-((2-chlorophenyl)methyl)-4,4-dimethyl- 3-isoxazolidinone; EPTC, S-ethyl dipropylcarbamothio- ate; imazethapyr, (?)-2-(4,5-dihydro-4-methyl-4-(1-meth- ylethyl)-5-oxo-lH-imidazol-2-yl)-5-ethyl-3-pyridinecarbox- ylic acid; metolachlor, 2-chloro-N-(2-ethyl-6- methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; pendimethalin, N-(1-ethylpropyl)-3,4-dimethyl-2,6- dinitrobenzenamine; navy bean, Phaseolus vulgaris L. var. navy 'C-20'; wheat, Triticum aestivum L. 'Frankenmuth'. Additional index words. Bioactivity, bioavailability, car- ryover, crop rotation, dry beans, persistence, residues.
TL;DR: In this paper, electron micrographs of spray droplet residual on wheat, sunflower, and kochia indicated that salts and various adjuvants applied with glyphosate affected deposit crystal content, thickness, and contact with the leaf surface.
Abstract: Scanning electron micrographs of spray droplet residual on wheat, sunflower, and kochia indicated that salts and various adjuvants applied with glyphosate affected deposit crystal content, thickness, and contact with the leaf surface. Spray deposits of glyphosate applied with diammonium sulfate contained distinct crystals, which related to enhanced toxicity of glyphosate applied alone, or to overcoming antagonism of glyphosate toxicity by calcium chloride, when applied to wheat. In general, glyphosate applied with antagonistic calcium chloride salt formed spray deposits that were amorphous, thick, and without crystals. Glyphosate sprayed with nonantagonistic diammonium sulfate and ammonium chloride salts had deposits with crystals and an evenly spread residue beneath the crystals. The various micrographs indicate that the antagonism of glyphosate phytotoxicity by salts may be in part from physical entrapment of glyphosate in the spray deposit. Glyphosate spray droplet residue contact with wheat, sunflower, and kochia surfaces related to observed differences in glyphosate toxicity to these species.
TL;DR: In this paper, a computer contour mapping was used to visualize spatial patterns of a population of common lambsquarters at three intervals during a growing season, and the seedbanks of six agricultural habitats were demonstrated to be floristically different based on the analysis of the relative abundance of weeds in each site using CDA.
Abstract: Seedbank studies often suffer from major methodological inadequacies such as absence of appropriate statistical data analysis and low sampling intensity. Multivariate analysis and computer mapping are innovative ways to treat seedbank data. Computer contour mapping was used to visualize spatial patterns of a population of common lambsquarters at three intervals during a growing season. At one site, high spring seed density of 600 000 seed m-2 was decreased to 18.3% of its original size by July, while at another site, low spring seedbank of common lambsquarters of 25 000 seed m-2 increased to 40 000 seed m-2 by autumn. Seedbank studies usually report results on total seed density or on densities of the most abundant species because of difficulties in analyzing large species matrices using parametric statistics. Multivariate analysis and specifically canonical discriminant analysis (CDA) are well suited for seedbank populations. The seedbanks of six agricultural habitats were demonstrated to be floristically different based on the analysis of the relative abundance of weed species in each site using CDA. Organic soils either under grassland or cultivated had significantly larger total seedbanks than mineral soils. If seedbanks are to be used in predictive population models, quantitative data that are reliable, rapidly obtained with limited resources, and logistically feasible for large sampling protocols are needed. Image analysis may be a potential rapid technique for weed seed recognition of washed soil samples.
TL;DR: In this paper, the effects of wild poinsettia interference with peanuts were investigated in Georgia and Florida during 1988 and 1989, and the predicted yield losses were 0, 4, 8, 12, 15, 26, 40, and 54% for season-long wild poinettia interference at densities of 0, 1, 2, 3, 5, 6, 7, 9, 14, 22, 30, 37, and 32 plants.
Abstract: Research was conducted during 1988 and 1989 in Georgia and Florida to determine the densitydependent effects and critical periods of wild poinsettia interference with peanut. Peanut yield loss ranged from 0 to approximately 50% over the wild poinsettia density range from 0 to 32 plants 9 m−1 peanut row. Predicted peanut yield losses across 2 yr in Georgia were 0, 4, 8, 12, 15, 26, 40, and 54% for season-long wild poinsettia interference at densities of 0, 1, 2, 3, 4, 8, 16, and 32 plants 9 m−1 of row, respectively. Across 2 yr in Florida, predicted peanut yield losses were 0, 9, 14, 22, 30, 37, and 41% for wild poinsettia densities of 0, 1, 2, 4, 8, 16, and 32 plants 9 m−1 row, respectively. Peanuts had to be maintained poinsettia free for 10 wk after peanut emergence to prevent yield loss. Wild poinsettia that interfered with peanut for more than 2 wk after peanut emergence reduced peanut yield.
TL;DR: Bentazon reduced paraquat phytotoxicity to Texas panicum, sicklepod, Florida beggarweed, and peanut as mentioned in this paper, but not to smallflower morningglory.
Abstract: Bentazon reduced paraquat phytotoxicity to Texas panicum, sicklepod, Florida beggarweed, and peanut. Bentazon applied alone had minimal effect on these species. Smallflower morningglory was more sensitive to bentazon than to paraquat; the interaction of paraquat and bentazon varied from antagonistic to synergistic depending upon the specific combination of rates. Antagonism with tank-mixed combinations was also obtained by applying bentazon prior to paraquat, but not with the reverse. Studies with 14C-labeled herbicides revealed that each herbicide inhibited foliar penetration of the other. In field studies, adding bentazon to paraquat reduced crop injury. However, except for smallflower morningglory, weed control was also reduced.
TL;DR: It is suggested that a shift in respiration and metabolism of fall-grown rosette- and bolt-plants leads to increased assimilate movement to the root which may have practical implications for control of this weed.
Abstract: Under field conditions, more photoassimilate moved to roots of Canada thistle at the bolt than at the bud, flower, or postflower stages. Similarly, greater photoassimilate accumulated in roots of Canada thistle in the greenhouse at the rosette and bolt than at the flower bud stage. Growth chamber experiments indicated that environmental conditions typical of fall, and possibly early spring, favored photoassimilate movement to the root and superseded growth stage control of assimilate partitioning. Allocation of assimilate within the root was strongly influenced by growth stage, with most assimilate being utilized for growth at the rosette stage and for fructan reserves in bolt and flower bud stages. Nomencla- ture: Canada thistle, Cirsium arvense (L.) Scop. #3 CIRAR. Additional index words. Phloem transport, carbohydrate
TL;DR: Tannin and lignin appear to function as barriers to microbial invasion resulting in higher shattercane seed resistance to overwinter demise as well as positively correlated with glume tightness, caryopsis lign in, and glume tannin.
Abstract: Shattercane seed survival during soil burial was highly dependent on attached glumes. Shattercane seed tightly enclosed by glumes averaged 5 and 53% germina- tion after 4 mo of winter burial in 1988 and 1989, respectively. Shattercane caryopses (seed without glumes) survival averaged 0.5 and 17% compared to 17 and 41% when treated with seed fungicides in 1988 and 1989, respectively. Shattercane caryopses tannin and lignin contents were higher than for cultivated sorghum caryopses. Glume tannin was four times higher and glume lignin was five times higher than in the caryopsis. Shattercane seed survival was positively correlated with glume tightness, caryopsis lignin, and glume tannin. Tannin and lignin appear to function as barriers to microbial invasion resulting in higher shattercane seed resistance to overwinter demise. Attempts to isolate fungal inhibitors from shattercane seed were unsuccessful. Nomenclature: Shattercane, Sorghum bicolor (L.)Moench #3 SORVU; sorghum, Sorghum bicolor (L.)Moench. Additional index words. Antifungal, glumes, lignin, seed burial, tannin.
TL;DR: Ammonium fertilizers, petroleum oil concen- trate, and nonionic surfactant were evaluated as post- emergence spray additives to improve giant foxtail and volunteer corn control by 28 g ai ha1 of the ethyl ester of quizalofop or 56 g ha-1 sethoxydim as discussed by the authors.
Abstract: Ammonium fertilizers, petroleum oil concen- trate, and nonionic surfactant were evaluated as post- emergence spray additives to improve giant foxtail and volunteer corn control by 28 g ai ha1 of the ethyl ester of quizalofop or 56 g ha-1 sethoxydim. Additions of 0.25% by vol nonionic surfactant or 2.5% petroleum oil concentrate improved grass control, but additions of 10% urea ammonium nitrate (28-0-0), 10% ammonium poly- phosphate (10-34-0), or 0.1M ammonium sulfate (21- 0-0-24S) did not consistently affect grass control. In laboratory studies with corn, greatest 14C absorption from leaf-applied 14C-quizalofop (8 h after treatment) was found with additions of petroleum oil concentrate (80% absorbed) or nonionic surfactant (18% absorbed), while less absorption was observed with treatments containing either no additive, urea ammonium nitrate, ammonium polyphosphate, or ammonium sulfate (8 to 13% ab- sorbed). Surface tension and droplet size of spray solutions were affected primarily by additions of nonionic surfactant, petroleum oil concentrate, and the formulated herbicides. Solution density, solute potential, pH, and buffering capacity were primarily affected by fertilizer additions. Nomenclature: Quizalofop, (?)-2-(4((6-chloro- 2-quinoxalinyl)oxylphenoxy)propanoic acid; sethoxydim, 2-(1-(ethoxyimino)butyll-5-(2-(ethylthio)propyl)-3- hydroxy-2-cyclohexen-1-one; giant foxtail, Setaria faberi Herrm. #3 SETFA; volunteer corn, Zea mays L. #
TL;DR: In this article, the effect of various factors on germination of dogfennel and yankeeweed was investigated and the results showed that both species were moderately tolerant to water stress.
Abstract: Laboratory studies were conducted to determine the effect of various factors on germination of dogfennel and yankeeweed. Dogfennel seed were found to be strongly photoblastic with no germination in the dark. Yankeeweed seed were moderately photoblastic, with 12% germination occurring in the absence of light Germination for both species increased in response to red light (650 nm), indicating phytochrome regulation. At the soil surface, dogfennel and yankeeweed emergence was 40 and 48%, respectively, but declined rapidly with increasing soil depths where dogfennel germination was lower than that of yankeeweed. Yankeeweed germination was 60 to 75% from 10 to 30 C while dogfennel germination was 45 to 70% between 15 to 30 C. Both species germinated over a broad range of pH (6 to 10) with the highest germination occurring at pH 8. Yankeeweed and dogfennel were moderately tolerant to water stress, but yankeeweed tolerated higher water stress than dogfennel. Both species germinated over a wide range of conditions, possibly enhancing adaptation to many diverse environments.