Showing papers in "Weed Science in 2000"
TL;DR: More than 300 rangeland weeds in the United States are known to cause an estimated loss of $2 billion annually in the USA, which is more than all other pests combined as mentioned in this paper.
Abstract: Rangeland and pastures comprise about 42% of the total land area of the United States. About three-quarters of all domestic livestock depend upon grazing lands for survival. Many ranges have had domestic stock grazing for more than 100 years and, as a result, the plant composition has changed greatly from the original ecosystems. Western rangelands previously dominated by perennial bunchgrasses have been converted, primarily through overgrazing, to annual grasslands that are susceptible to invasion by introduced dicots. Today there are more than 300 rangeland weeds in the United States. Some of the most problematic include Bromus tectorum, Euphorbia esula, Centaurea solstitialis, C. diffusa, C. maculosa, and a number of other Centaurea species. In total, weeds in rangeland cause an estimated loss of $2 billion annually in the United States, which is more than all other pests combined. They impact the livestock industry by lowering yield and quality of forage, interfering with grazing, poisoning a...
713 citations
TL;DR: Mulch area index was a pivotal property for quantitatively defining mulch properties and understanding weed emergence through mulches and a two-parameter model of emergence as a function of mul ch area index and fraction of mulch volume reasonably predicted emergence across the range of mulches investigated.
Abstract: Mulches on the soil surface are known to suppress weed emergence, but the quantitative relationships between emergence and mulch properties have not been clearly defined. A theoretical framework for describing the relationships among mulch mass, area index, height, cover, light extinction, and weed emergence is introduced. This theory is applied to data from experiments on emergence of four annual weed species through mulches of selected materials applied at six rates. Mulch materials, in order from lowest to highest surface-area-to-mass ratio, were bark chips, Zea mays stalks, Secale cereale, Trifolium incarnatum, Vicia villosa, Quercus leaves, and landscape fabric strips. The order of weed species' sensitivity to mulches was Amaranthus retroflexus > Chenopodium album > Setaria faberi > Abutilon theophrasti, regardless of mulch material. The success of emergence through mulches was related to the capacity of seedlings to grow around obstructing mulch elements under limiting light conditions. Mul...
435 citations
TL;DR: Herbicide rate and timing recommendations for mixed populations of these weeds should be based on A. palmeri because of its high growth rates, and recent increases in species range and observed changes in weed community structure may be partially explained by the growth characteristics of A. Palmeri and A. albus.
Abstract: A 2-yr field study was conducted to compare the growth of Amaranthus palmeri, A. rudis, A. retroflexus, and A. albus planted in June and July. Rates of height increase (centimeters per growing degree day) were 0.21 and 0.18 for A. palmeri, 0.16 and 0.11 for A. rudis, 0.12 and 0.09 for A. retroflexus, and 0.08 and 0.09 for A. albus in 1994 and 1995, respectively, when planted in June. A. palmeri had among the highest values for plant volume, dry weight, and leaf area, while A. albus had the lowest. Specific leaf area values (cm2 g−1) ranged from 149 to 261 for A. palmeri, 160 to 205 for A. rudis, 150 to 208 for A. retroflexus, and 127 to 190 for A. albus. Maximum relative growth rates (g g−1 day−1) for any measured period were 0.32 for A. palmeri, 0.31 for A. rudis, 0.30 for A. retroflexus, and 0.26 for A. albus. Recent increases in species range and observed changes in weed community structure may be partially explained by the growth characteristics of A. palmeri and A. rudis. Herbicide rate and ...
356 citations
TL;DR: Herbicide mechanisms that are dependent on light or are enhanced by light fall into several different categories, and in all instances the involvement of light in herbicide action is not a direct interaction of light and herbicide at the primary site of action.
Abstract: Activities of a surprisingly large number of herbicide families are directly or indirectly influenced by light. Herbicide mechanisms that are dependent on light or are enhanced by light fall into several different categories. These herbicides inhibit electron flow in photosystem II in the photosynthetic light reaction (e.g., triazines, phenyl ureas, and uracils), capture electrons in photosystem I in the photosynthetic light reaction (e.g., bipyridiniums such as paraquat), inhibit glutamine synthetase in the nitrogen assimilation pathway (e.g., glufosinate), inhibit protoporphyrinogen oxidase during chlorophyll biosynthesis (e.g., diphenyl ethers [DPEs] and N-phenyl heterocycles), directly inhibit carotenoid biosynthesis by inhibiting one of the desaturase enzymes (e.g., norflurazon and fluridone), or indirectly inhibit carotenoid biosynthesis by inhibiting a quinone cofactor involved in the desaturase reaction (e.g., triketones and isoxazoles). Surprisingly, in all instances the involvement of light in herbicide action is not a direct interaction of light and herbicide at the primary site of action. In addition, the events that cause tissue damage (necrosis) are not associated with the primary target and are always due to membrane damage caused by lipid peroxidation of polyunsaturated fatty acids.
318 citations
TL;DR: In this article, the effect of increasing glyphosate application rate on soil microbial biomass and activity was investigated in Weswood silt loam, where the isopropylamine salt of glyphosate was added at rates of 47, 94, 140, and 234 µg ai g−1 soil based on an assumed 2mm glyphosate interaction depth.
Abstract: Herbicides applied to soils potentially affect soil microbial activity. Quantity and frequency of glyphosate application have escalated with the advent of glyphosate-tolerant crops. The objective of this study was to determine the effect of increasing glyphosate application rate on soil microbial biomass and activity. The soil used was Weswood silt loam. The isopropylamine salt of glyphosate was added at rates of 47, 94, 140, and 234 µg ai g−1 soil based on an assumed 2-mm glyphosate–soil interaction depth. Glyphosate significantly stimulated soil microbial activity as measured by C and N mineralization but did not affect soil microbial biomass. Cumulative C mineralization, as well as mineralization rate, increased with increasing glyphosate rate. Strong linear relationships between mineralized C and N and the amount of C and N added as glyphosate (r2 = 0.995, 0.996) and slopes approximating one indicated that glyphosate was the direct cause of the enhanced microbial activity. An increase in C mi...
290 citations
TL;DR: A field in which Brassica napus volunteers were not controlled by several applications of glyphosate was investigated in 1998 as discussed by the authors, and 15 volunteers had progeny that were 66 and 82% resistant to glyphosate, consistent with the predicted 3:1 resistant : susceptible ratio.
Abstract: A field in which Brassica napus volunteers were not controlled by several applications of glyphosate was investigated in 1998. This field had been planted with glufosinate-resistant and imidazolinone-resistant B. napus in 1997 and was adjacent to a field that had grown glyphosate-resistant B. napus. Mature volunteer B. napus were collected on a 50- by 100-m grid in the field. Progeny from 34 volunteers were sprayed with glyphosate at 440 g ae ha−1, and the survivors were sprayed with either glufosinate or imazethapyr at 400 or 50 g ai ha−1, respectively. Where seed numbers permitted (14 volunteers), seedlings were also sprayed sequentially with glyphosate, glufosinate, and imazethapyr, at 440 g ae ha−1, 400 g ai ha−1, and 50 g ai ha−1, respectively. In total, 15 volunteers had progeny that were between 66 and 82% resistant to glyphosate, consistent with the predicted 3:1 resistant : susceptible ratio. Volunteer B. napus plants with glyphosate-resistant seedlings were most common close to the puta...
280 citations
TL;DR: This review covers the topic of weed/arthropod interactions, and provides the reader with access to literature in the subject area that is scattered in weed science, entomological, crop production, and ecological journals, to indicate where multidisciplinary research involving weed and arthropod management should be focused in the future.
Abstract: Interactions between weeds and arthropods occur frequently. This review covers the topic of weed/arthropod interactions, and provides the reader with access to literature in the subject area that is scattered in weed science, entomological, crop production, and ecological journals. We first analyze the current status of weed and arthropod management in the context of multidisciplinary integrated pest management (IPM). The remainder of the review is organized according to the mechanisms driving interactions. The first section deals with interactions driven by trophic relationships, and is subdivided into direct and indirect trophic interactions. Direct trophic interactions occur when pest or beneficial arthropods feed directly on weeds. Indirect trophic interactions occur when arthropod feeding damage to crops impacts weeds through alteration of ecosystem resource availability, or through weeds serving as hosts for alternate prey for beneficial arthropods, or via tritrophic interactions. The second mechanism driving interactions is considered in relation to alteration of the physical habitat by the presence of weeds, such as alteration of temperature within the plant canopy. The third major mechanism driving interactions is based on control tactics for the two types of pests. These are considered from the aspect of direct physical effects, such as tillage, and from the aspect of interactions resulting from the use of pesticides. The latter is divided into direct effects of herbicides and insecticides on non-target pests and beneficials, and on interactions that result from alteration of host plant physiology by pesticides. A conclusion section attempts to place the impact of interactions into an IPM framework, and to indicate where multidisciplinary research involving weed and arthropod management should be focused in the future.
262 citations
TL;DR: The results suggest that the spread potential of C. radicans by seeds would be at least 1,400 to 2,800 seeds plant−1, however, only seeds near the soil surface would be able to germinate.
Abstract: The effects of environmental factors on germination and emergence of Campsis radicans seeds were examined in laboratory and greenhouse experiments. Campsis radicans pods produced numerous, papery, and small seeds (696 seeds/pod; 4 mg/seed). Seeds exhibited dormancy that was relieved (74% germination) after 2 wk of prechilling. Fluctuating temperatures and a 12-h photoperiod were required for maximum germination. Optimum conditions for C. radicans seed germination (74%) were 35/25 C (day/night, 12/12 h) with a 12-h photoperiod. Temperatures below 25/15 C or above 40/30 C were unfavorable for germination. Germination in constant temperatures or in continuous darkness was less than 15%. More than 59% of C. radicans seeds germinated at pH 5 to 9, but at pH 4 or 10 seed germination was totally inhibited. Germination was totally inhibited at osmotic stress higher than −0.2 MPa. Germination was 60% at 40 mM NaCl and 20% at 160 mM NaCl. Emergence was maximum (68%) for seeds that were placed on the soil s...
226 citations
TL;DR: In this paper, the application of IPM to weed management has lagged behind other pe... The basic principles of IPM are well established and have been successfully applied to many agricultural pests.
Abstract: Modern weed control tactics have played a major role in the productivity of cropping systems. Herbicides have been an effective component of weed control for major crops, greatly reducing yield losses and facilitating reduced tillage systems. Although these benefits are important, weed problems, soil erosion, and environmental concerns persist. Herbicides will continue to play a key role in most production systems, but weed species will continue to evolve and weed communities shift in response to selection pressures. Weed science must develop and incorporate additional practices to create integrated management systems that diversify selection pressures and reduce environmental degradation. Integrated pest management (IPM) may provide a useful framework for the development of integrated weed management systems. The basic principles of IPM are well established and have been successfully applied to many agricultural pests. However, the application of IPM to weed management has lagged behind other pe...
162 citations
TL;DR: The repeated use of the few available grass herbicides in the predominantly monocultured O. sativa of California has selected for herbicide resistance in E. oryzoides and E. phyllopogon, highlighting the need to integrate herbicide use with nonchemical means of weed management.
Abstract: Echinochloa oryzoides and E. phyllopogon have become the most serious weeds in California Oryza sativa since continuous flooding was used to suppress E. crus-galli. Continuous use of a limited number of available graminicides and an increasing number of control failures led to the investigation of herbicide resistance in E. oryzoides and E. phyllopogon. Greenhouse dose-response studies with postemergence (POST) applications of molinate, thiobencarb, fenoxaprop-ethyl, and bispyribac-sodium estimating GR50 (herbicide dose to inhibit growth by 50%) values suggested resistance to all herbicides in two E. phyllopogon accessions and to molinate and thiobencarb in one E. oryzoides accession when compared with susceptible E. phyllopogon and E. oryzoides controls, respectively. No resistance was detected in dose-response studies with propanil. Minimum and maximum ratios (R/S) of the GR50 values of resistant to susceptible E. phyllopogon plants (in two experiments involving two resistant accessions) were 7...
158 citations
TL;DR: A database of noxious weed lists obtained from the 48 continental states and six bordering provinces is compiled, finding that biological control programs have targeted many of the top dicotyledonous weeds of national concern, but none of the weedy grasses and sedges.
Abstract: To identify the most commonly regulated weedy plants in the United States and southern Canada, we compiled a database of noxious weed lists obtained from the 48 continental states and six bordering provinces. The 10 most frequently listed weeds are Cirsium arvense, Carduus nutans, Lythrum spp. (includes purple loosestrife), Convolvulus arvensis, Euphorbia esula, Acroptilon repens, Sorghum spp. (includes johnsongrass and shattercane), Cardaria spp. (includes hoary cress, also called whitetop), Centaurea maculosa, and Sonchus arvensis. When genera are ranked, the top genus is Centaurea, which includes C. maculosa, C. diffusa, and C. solstitalis. Biological control programs have targeted many of the top dicotyledonous weeds of national concern, but none of the weedy grasses and sedges. We recommend that exploratory studies be initiated to determine the feasibility of developing biological control agents for the latter species. The complete database of noxious weed lists is available on the Internet ...
TL;DR: Biomass at tillering was the best predictor of modern cultivar competitiveness against weeds, whereas relative growth rate, net assimilation rate, and tillering capacity of O. sativa were not.
Abstract: This study was conducted in lowland fields at the International Rice Research Institute in the 1994 wet season and the 1995 dry season to determine Oryza sativa plant traits that confer competitive ability against weeds when pregerminated seeds are sown on puddled soil. Initial biomass (IB), crop growth rate (CGR), leaf area index (LAI), and biomass at tillering of O. sativa plants were associated with their competitiveness against weeds, whereas relative growth rate, net assimilation rate, and tillering capacity of O. sativa were not. Biomass at tillering affected weed biomass directly, and IB, CGR, and LAI indirectly affected weed biomass through O. sativa biomass. Biomass at tillering was the best predictor of modern cultivar competitiveness against weeds. Nomenclature: Oryza sativa L., rice.
TL;DR: In this article, the emergence phenology of C. album seedlings was predicted with greater accuracy under no-till and moldboard plow systems than under a chisel plow system.
Abstract: Studies were conducted to develop a model from field and laboratory studies to predict the emergence phenology of Chenopodium album. A mechanistic model to predict the phenology of weed seedling emergence across locations, years, and tillage systems is presented. This was accomplished by the integration of hydrothermal time to describe germination and thermal time to describe shoot elongation. The interaction of soil moisture and temperature in the model was accounted for by the integration of hydrothermal time in algorithms predicting seed germination. Soil temperatures within the weed seed germination zone were predicted by temperature ranges at different depths in the soil. Emergence phenology of C. album seedlings was predicted with greater accuracy under no-till and moldboard plow systems than under a chisel plow system. We attributed this lower accuracy in the chisel plow system to increased heterogeneity in the soil matrix and vertical distribution of the seedbank caused by the chisel plow...
TL;DR: Differential activities of BOA, DIBOA, and crude water extract of Secale cereale ‘Elbon’ were studied in culture dish bioassays using several vegetable and weed species and indicated a promising potential for controlling small-seeded weeds in large-seeding crops.
Abstract: Differential activities of BOA, DIBOA, and crude water extract of Secale cereale ‘Elbon’ were studied in culture dish bioassays using several vegetable and weed species. On average, DIBOA was about seven times more inhibitory to root growth and four times more inhibitory to shoot growth than BOA. Allelochemicals from S. cereale inhibited shoot more than root elongation of cucurbits Cucumis melo, Cucumis sativus, and Cucurbita pepo. Small-seeded crops Lycopersicon esculentum and Lactuca sativa were sensitive to S. cereale. Large-seeded crops, including the cucurbits and Zea mays var. rogusa, were tolerant. Among the small-seeded weeds Amaranthus palmeri, Digitaria sanguinalis, Echinochloa crus-galli, and Eleusine indica, E. crus-galli was least susceptible. Inhibition of germination by BOA or DIBOA occurred only in small- to medium-seeded species, including A. palmeri, D. sanguinalis, E. indica, L. sativa, L. esculentum, and Sida spinosa. Large-seeded species C. melo, C. sativus, C. melopepo, Z. m...
TL;DR: The results indicate a single glyphosate application can prevent yield loss in narrow-row, glyphosate-resistant G. max under favorable conditions, but application timing becomes more critical in wide rows because the critical period of weed removal occurs earlier.
Abstract: Field experiments were conducted in 1996 and 1997 to determine the effect of the rate and time of glyphosate application on weed emergence, survival, biomass, and Glycine max yield in reduced-tillage (RT) and no-tillage (NT) glyphosate-resistant G. max planted in rows spaced 18 (narrow-row) and 76 cm (wide-row). Glyphosate was applied at 0.42, 0.63, and 0.84 kg ae ha−1 at V2, V4, R1, and R4 growth stages. On separate plots, 0.84 kg ha−1 glyphosate was applied at each growth stage with hand weeding. A weed-free check was maintained with preemergence imazethapyr plus metolachlor supplemented with hand weeding, and a nontreated check was included. Weed population density before glyphosate application ranged from 239 to 606 plants m−2 in RT and 33 to 500 plants m−2 in NT systems. Setaria faberi and Chenopodium album were the predominant species. Weed control efficacy and crop yield were influenced more by application time than by glyphosate rate. Glyphosate applied at V2, V4, and R1 gave season-long ...
TL;DR: Current remote sensing technology has potential for in-season weed detection; however, further advancements of the technology are needed to insure its use in future prescription weed management systems.
Abstract: The objective of this research was to evaluate the accuracy of remote sensing for detecting weed infestation levels during early-season Glycine max production. Weed population estimates were collected from two G. max fields approximately 8 wk after planting during summer 1998. Seedling weed populations were sampled using a regular grid coordinate system on a 10- by 10-m grid. Two days later, multispectral digital images of the fields were recorded. Generally, infestations of Senna obtusifolia, Ipomoea lacunosa, and Solanum carolinense could be detected with remote sensing with at least 75% accuracy. Threshold populations of 10 or more S. obtusifolia or I. lacunosa plants m−2 were generally classified with at least 85% accuracy. Discriminant analysis functions formed for detecting weed populations in one field were at least 73% accurate in identifying S. obtusifolia and I. lacunosa infestations in independently collected data from another field. Due to highly variable soil conditions and their eff...
TL;DR: The size, location, and variation in time of weed patches within an arable field were analyzed with the ultimate goal of simplifying weed mapping and found aggregation of seedlings into patches was strongest for annuals and, more generally, for species whose seeds were dispersed by combine harvesting.
Abstract: The size, location, and variation in time of weed patches within an arable field were analyzed with the ultimate goal of simplifying weed mapping. Annual and perennial weeds were sampled yearly from 1993 to 1997 at 410 permanent grid points in a 1.3-ha no-till field sown to row crops each year. Geostatistical techniques were used to examine the data as follows: (1) spatial structure within years; (2) relationships of spatial structure to literature-derived population parameters, such as seed production and seed longevity; and (3) stability of weed patches across years. Within years, densities were more variable across crop rows and patches were elongated along rows. Aggregation of seedlings into patches was strongest for annuals and, more generally, for species whose seeds were dispersed by combine harvesting. Patches were most persistent for perennials and, more generally, for species whose seeds dispersed prior to expected dates of combine harvesting. For the most abundant weed in the field, th...
TL;DR: Experiments comparing wild-type A. thaliana plants to mutant lines deficient in flavonoid biosynthesis revealed no differences in the ability to stimulate germination or to allow tubercle formation, indicating that host flavonoids production is not essential for Orobanche parasitization.
Abstract: Parasitization by Orobanche is a complex process, one that is mediated by host-derived chemical signals that control parasite seed germination and haustorium initiation and one that ultimately results in the union of two plant species. Experiments were conducted to characterize Orobanche parasitization of the model plant Arabidopsis thaliana and to begin to explore the role of host flavonoid metabolism in the interaction. Arabidopsis thaliana stimulated seed germination and allowed tubercle development of O. aegyptiaca and O. ramosa but did not significantly stimulate seeds of O. crenata, O. minor, or O. cernua. However, if Orobanche seeds were artificially stimulated, O. crenata and O. minor successfully established tubercles on A. thaliana. When compared to the recognized crop hosts, Daucus carota and Nicotiana tabacum, A. thaliana stimulated less O. aegyptiaca germination but allowed for formation of equivalent numbers of tubercles. These findings indicate that A. thaliana is not a large-scale...
TL;DR: Several consistent associations were identified across years, indicating that site properties can influence weed abundance, however, annual variation in the associations may be attributed to differences in agronomic and weed management practices for each crop, as well as temporal weather variation influencing weed abundance from year to year.
Abstract: Site properties and weed species abundance are known to vary spatially across fields. The extent to which they covary is not well understood. The objective of this research was to assess how canonical correlation analysis could be used to identify associations among site properties and weed species abundance within an agricultural field. A farmer-managed field rotated between Zea mays and Glycine max in Boone County, IA, was grid-sampled for site properties in 1992 and for weed species abundance between 1994 and 1997. Twelve site properties were considered in relation to five weed species that were identified and counted after all weed control operations were completed. Site properties such as total nitrogen, Bray-1 P, percent organic carbon, and texture were spatially variable. Weed species abundance was also spatially variable such that most weeds were found in patches and much of the field was weed-free. Canonical correlation analysis identified one to four significant correlations between lin...
TL;DR: Growth chamber and laboratory experiments were conducted to evaluate foliar absorption and translocation of the isopropylamine (Ipa) or trimethylsulfonium (Tms) salts of glyphosate in Abutilon theophrasti and Setaria faberi as mentioned in this paper.
Abstract: Growth chamber and laboratory experiments were conducted to evaluate foliar absorption and translocation of the isopropylamine (Ipa) or trimethylsulfonium (Tms) salts of glyphosate in Abutilon theophrasti and Setaria faberi. Glyphosate was applied at 250 g ai ha−1. Absorption of 14C-glyphosate in both formulations increased similarly in both species over 72 h. Seventy-two hours after treatment (HAT), A. theophrasti absorbed 26% of applied 14C of both formulations, whereas S. faberi absorbed 43% of both formulations. The addition of 1% ammonium sulfate (AMS) to both formulations increased the amount of herbicide absorbed to 35% in A. theophrasti and 60% in S. faberi 72 HAT. Translocation of absorbed 14C-glyphosate in both formulations (with or without AMS) was greater for S. faberi than A. theophrasti 72 HAT. For A. theophrasti, 17% of 14C absorbed in Ipa and Tms formulations were translocated out of the treated leaf, whereas additions of AMS increased the amount translocated to 25 and 23% for Ipa...
TL;DR: In this paper, the authors evaluated the effect of temperature and soil moisture on Triticum aestivum efficacy and metabolism and found that the effectiveness of spray application of 24 and 46 g ha−1 MON 37500 was greater when the soil moisture was at full pot capacity than when the temperature was at 5/3 C after application.
Abstract: Spray application of 24 and 46 g ha−1 MON 37500 was used in efficacy studies, and vacuum infiltration or droplet application of radiolabeled MON 37500 was used in metabolism studies to evaluate temperature and soil moisture on MON 37500 efficacy and metabolism. Day/night temperatures before vs. after application of MON 37500 of 25/23 vs. 25/23, 25/23 vs. 5/3, 5/3 vs. 25/23, and 5/3 vs. 5/3 C were evaluated for the efficacy study, whereas day/night temperatures of 5/3 and 25/23 C were used for the metabolism study. Soil moisture of one-third and full pot capacities was evaluated for both studies. No Triticum aestivum injury was observed at the different temperatures or soil moistures because of rapid metabolism of MON 37500 by T. aestivum. Weed control was greater when the temperature after application was 25/23 C or soil moisture was at full pot capacity than when the temperature was at 5/3 C after application or soil moisture was at one-third pot capacity. Susceptibility to MON 37500 was greates...
TL;DR: Unique long-term historical emergence records were used to assess the association between weed seedling emergence and various elements of meteorological data, indicating that temperature was the dominant factor in predicting emergence.
Abstract: Unique long-term historical emergence records were used to assess the association between weed seedling emergence and various elements of meteorological data. These elements included both temperature-based and rainfall-related variables in the 7-d periods before and during which emergence occurred. Five weed species (Stellaria media, Chenopodium album, Capsella bursa-pastoris, Matricaria perforata, and Veronica hederifolia) with contrasting emergence patterns were studied in disturbed soil. Logistic regression analysis was used to identify meteorological variables of interest and allowed their relative importance to be assessed and ranked. Logistic regression was further used to associate probabilities of emergence with observed levels of important individual meteorological elements. This approach enabled prediction of the probability of emergence following given meteorological conditions and hence an assessment of the risk of omitting weed control measures. Predictions were made based on single ...
TL;DR: Sesbania exaltata seed production and seedling emergence of three broadleaf weed species were evaluated following glyphosate application at initial seed set, mid seed fill, and physiological maturity, with results indicating inconsistency in response in the field.
Abstract: Seed production and seedling emergence of three broadleaf weed species were evaluated following glyphosate application at initial seed set, mid seed fill, and physiological maturity. In greenhouse experiments averaged across glyphosate rates of 0.42, 0.63, and 0.84 kg ae ha−1, Xanthium strumarium 100-bur weight and burs per plant were reduced at least 69 and 70%, respectively, for application at initial fruit set compared with later applications, and seedling emergence was 3% of the nontreated check. Glyphosate application at initial seed set reduced Sesbania exaltata 100-seed weight 73%, seed per plant 86%, and seedling emergence 94%. Senna obtusifolia 100-seed weight, seed per plant, and seedling emergence were reduced 46, 83, and 66%, respectively, when glyphosate was applied at initial seed set. In field experiments, X. strumarium and S. exaltata seed production were reduced only when glyphosate was applied at initial seed set. Compared with the nontreated check, seedling emergence following ...
TL;DR: It was hypothesized that management practices strongly interacted with site properties to create the observed associations with weed populations, and hypothesized mechanisms for weed patchiness include patchiness in available soil moisture that would influence weed seed germination, emergence, and seedling growth.
Abstract: Identification of associations between site properties and weed species abundance led to the generation of hypotheses as to why weed populations occur where they do, or do not, in agricultural fields. The objective of this research was to use a multivariate statistical technique, canonical correlation analysis, to identify the associations. Two continuous Zea mays production fields under center-pivot irrigation in the central Platte River Valley of Nebraska were grid-sampled between 1994 and 1997 for nine site properties and six to seven weed species. Weed species were identified and counted just prior to postemergence weed control in two adjacent quadrats (1 by 0.38 m) at each grid sampling point. These quadrats represented untreated weed populations emerging between crop rows and treated populations that survived preemergence herbicide banded within the crop row. Canonical correlation analysis identified one to five significant correlations between linear combinations of site properties and wee...
TL;DR: It is suggested that AMS can increase the efficacy of glufosinate on A. theophrasti and S. faberi by increasing foliar absorption and subsequent translocation of glUFosinate.
Abstract: The effect of ammonium sulfate (AMS) on efficacy, absorption, and translocation of glufosinate in various weed species was investigated in greenhouse and field experiments. Adding ammonium sulfate at 20 g L−1 increased the efficacy of glufosinate on Echinochloa crus-galli, Setaria faberi, and Abutilon theophrasti, but not on Amaranthus rudis or Chenopodium album. AMS increased foliar absorption of 14C from 14C-glufosinate to the greatest extent in A. theophrasti and S. faberi and to the least extent in C. album. AMS increased the translocation of 14C out of the treated leaf 24 h after treatment in A. theophrasti and S. faberi, but not in C. album. These results suggest that AMS can increase the efficacy of glufosinate on A. theophrasti and S. faberi by increasing foliar absorption and subsequent translocation of glufosinate. Nomenclature: Glufosinate, Echinochloa crus-galli (L.) Beauv. ECHCG, barnyardgrass; Chenopodium album L. CHEAL, common lambsquarters; Amaranthus rudis Sauer AMATA, common wat...
TL;DR: A Avena fatua seeds remaining on the plant at harvest and taken into the combine harvester may be dispersed over large areas and the proportion of seed remaining on A. fatua at harvest could be managed by changing the timing of crop harvest.
Abstract: Avena fatua seeds remaining on the plant at harvest and taken into the combine harvester may be dispersed over large areas. The objective of this study was to characterize the development of A. fatua in comparison to spring Triticum aestivum. As part of this objective, the rate of seed shed in A. fatua relative to development of T. aestivum was determined. Avena fatua and T. aestivum had similar phyllochron intervals within locations but differed between locations. Plant development as measured by the Zadoks plant development scale was consistent within plant species between locations. Seed shed in A. fatua was also consistent between locations. Most of the seed shed occurred within 2 wk, and the cumulative seed shed followed a sigmoidal pattern. The seed shed occurred as T. aestivum was ripening, and the percentage of seed shed appears to be related to the water content of the T. aestivum spike. Because of this relationship, the proportion of seed remaining on A. fatua at harvest could be manage...
TL;DR: Because rate of spread is more dependent on dispersal than on demographic factors, greater attention needs to be given to describing dispersal frequency distributions and especially to analysis of their shapes.
Abstract: A model is presented of the spread of a weed from a point source, with dispersal being both unaided and aided by a combine harvester. Four “type” weeds were modeled, chosen to represent species of differing population and dispersal ecologies and based broadly on Avena spp. (wild oats), Raphanus raphanistrum (wild radish), Bromus spp. (bromegrass), and Fumaria spp. (fumitory). Wind-adapted species were excluded. The greatest rate of spread was predicted to be for R. raphanistrum and the least for Fumaria, regardless of whether dispersal by combine harvester was included. Rate of spread was more sensitive to dispersal parameters than to demographic parameters and increased up to 16-fold as soon as any seeds were dispersed by the harvester. Given that uptake by the harvester is a function of phenology of seed production and dispersal, better data on such processes is required for weeds. Because rate of spread is more dependent on dispersal than on demographic factors, greater attention needs to be g...
TL;DR: Differences in the depth of weed seedling recruitment due to agronomic management practices, such as reduced tillage, have implications for weed competitive ability and management strategies and should be specific to tillage and sampling time.
Abstract: Differences in the depth of weed seedling recruitment due to agronomic management practices, such as reduced tillage, have implications for weed competitive ability and management strategies. Depth of seedling recruitment of Avena fatua, Triticum aestivum, Setaria viridis, Polygonum convolvulus, and Echinochloa crus-galli was measured in situ in 1997 and 1998 prior to seeding (preseeding) and before in-crop spraying (prespray) in a total of 44 zero-tillage and 44 conventional-tillage fields located across approximately 3 million ha of southern Manitoba, Canada. For the monocot species, depth of recruitment was measured from the soil surface to the intact seed coats, which marked the point of germination. For P. convolvulus, a dicot, greenhouse studies were conducted prior to sampling in the field to identify a reliable morphological marker indicating the point of germination. For all species, mean recruitment depth was found to be significantly shallower in zero- vs. conventional-tillage fields a...
TL;DR: In this paper, the authors discuss the issue and offer suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement.
Abstract: Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement. Nomenclature: Readers are referred to the WSSA Herbicide Handbook...
TL;DR: It is demonstrated for the first time that a fungal protein can cause extensive necrosis when applied to weed species as a foliar spray.
Abstract: A small assortment of microbial proteins have the ability to activate defense responses and induce necrosis in plant cells through cell signaling pathways. These proteins are of interest because of their potential use as bioherbicides and inducers of plant resistance in agriculture. A 24-kDa protein (Nep1) was purified from culture filtrates of Fusarium oxysporum, and the effects of this protein on weed leaves were investigated. This protein induced necrosis in detached leaves of Papaver somniferum, Lycopersicon esculentum, Malva neglecta, and Acroptilon repens when taken up through the petiole. The pattern and level of necrosis were dependent on the plant species. Treatment with Nep1 induced the production of ethylene in isolated leaves of various species, and the level of ethylene response was shown to be correlated to the concentration of the protein. Pretreating leaves of P. somniferum, L. esculentum, M. neglecta, and Cardaria draba with 100 µl L-1 ethylene enhanced the protein induction of e...