Use Of Selective Herbicides Research Articles

Dissipation Kinetics, Leaching, and Ecological Risk Assessment of S-Metolachlor and Benfluralin Residues in Soil

The use of selective herbicides is one of the best methods for weed management. However, the extensive use of herbicides can have adverse impacts on non-target organisms. The goals of this study were to assess the dissipation kinetics, leaching, and ecological risk assessment of S-metolachlor and benfluralin residues in silty loam soil planted with chickpea (Cicer arietinum L.). The experimental setup included four different layers with four replications corresponding to an experimental randomized complete block design consisting of 16 plots. The application doses of S-metolachlor and benfluralin were 1350 and 1920 g a.i./ha, respectively, according to manufacturer recommendations. Soil samples were split into four depths, 0 to 20 cm (Layer A), 20 to 40 cm (Layer B), 40 to 60 cm (Layer C), and 60 to 80 cm (Layer D), to determine the dissipation kinetics and the leaching behavior of the herbicides. Gas chromatography coupled with the electron capture detector (GC-ECD) method was developed and validated for the determination of S-metolachlor and benfluralin residues in soil. The analytes were extracted from the soil with distilled water and ethyl acetate followed by solid-phase extraction (SPE). The limit of quantification (LOQ) of the method was 0.1 μg/g, and the recoveries of S-metolachlor and benfluralin were in the ranges 81% to 97% and 88% to 101%, respectively, with relative standard deviations (RSD) of less than 9.7%. The dissipation kinetics of S-metolachlor and benfluralin in soil (0–20 cm) followed first-order kinetics with half-lives of 21.66 and 30.13 days, respectively. The results for samples obtained from the 20–80 cm soil profile showed that both benfluralin and S-metolachlor presented high leaching, following preferential flow. Also, a soil ecological risk assessment was conducted in the top 0–20 cm soil profile, estimating the toxicity–exposure ratio (TER) for four soil organisms and the risk quotient (RQ). The mean herbicide levels found at the studied soil profile at 0 days (2 h) and 60 days of the experiment were used for risk assessment. In the first case, the mean pesticide concentration (MPC) gives a worst-case scenario (ws); in the second case, a dissipation scenario (ds) is given using the respective MPC. In all cases, both TER and RQ values showed that benfluralin corresponds to a higher risk than S-metolachlor for soil organisms.

Flooding depths and burial effects on seedling emergence of five California weedy rice (Oryza sativa spontanea) accessions

AbstractWeedy rice (Oryza sativa f. spontanea Roshev.) has recently become a significant botanical pest in California rice (Oryza sativa L.) production systems. The conspecificity of this pest with cultivated rice negates the use of selective herbicides, rendering the development of nonchemical methods a necessary component of creating management strategies for this weed. Experiments were conducted to determine the emergence and early growth responses of O. sativa spontanea to flooding soil and burial conditions. Treatment combinations of four flooding depths (0, 5, 10, and 15 cm) and four burial depths (1.3, 2.5, 5, and 10 cm) were applied to test the emergence of five O. sativa spontanea accessions as well as ‘M-206’, a commonly used rice cultivar in California, for comparison. Results revealed that burial depth had a significant effect on seedling emergence. A 43% to 91% decrease in emergence between seedlings buried at 1.3 and 2.5 cm depending on the flooding depth and accession and an absence of emergence from seedlings buried at or below 5 cm were observed. Flooding depth did not affect emergence, but there was a significant interaction between burial and flooding treatments. There was no significant difference between total O. sativa spontanea emergence from the soil and water surfaces regardless of burial or flooding depths, implying that once the various accessions have emerged from the soil they will also emerge from the floodwater. Most accessions had similar total emergence compared with M-206 cultivated rice but produced more dry weight than M-206 when planted at 1.3 cm in the soil. The results of this experiment can be used to inform stakeholders of the flooding conditions necessary as well as soil burial depths that will promote or inhibit the emergence of California O. sativa spontanea accessions from the weed seedbank.

Impacts of herbicide sequences and vertical tuber distribution on the chemical control of yellow nutsedge (Cyperus esculentus L.)

AbstractCyperus esculentus is an invasive perennial sedge threatening agricultural production. In Belgium, best in‐crop control options involve, amongst other methods, growing maize in monoculture which allows the sequential use of selective herbicides with activity against C. esculentus. Two pot experiments were carried out to investigate the effect of genetically different clones and chemical control strategy on C. esculentus control. Additionally, the effect of two vertical tuber distributions (uniform in the 0–26 cm layer or non‐uniform with 60% of the tubers in the 6 cm top‐layer) was studied. Strategies were based on S‐metolachlor, dimethenamid‐P, mesotrione, bentazon, pyridate, nicosulfuron, glyphosate, halosulfuron‐methyl, foramsulfuron and thiencarbazon‐methyl used in mixture and/or sequence and applied at different crop stages. Control efficacy was measured by analysing tuber number, dry tuber biomass and above‐ground dry biomass. Tuber number of clones treated by chemical control strategies was up to 100% lower and up to 41% higher relative to the untreated control. Clones showed up to 74% percentage point difference in control of tuber number. In both experiments, strategies with pre‐plant incorporated dimethenamid‐P followed by two post‐emergence applications of mesotrione and pyridate, in 5–6 leaf and 8–9 leaf stage of maize, was most effective and consistent across C. esculentus clones. In general, C. esculentus control was up to 27% better in plots with high proportion of superficially buried mother tubers than in plots with more uniform vertical mother tuber distribution. Hence, the vertical tuber distribution may significantly affect the performance of C. esculentus herbicidal strategies. Overall, chemical control strategies should be complemented with alternative methods (e.g. competitive cropping systems and non‐inversion tillage) to achieve satisfactory control.

Herbicides glyphosate and glufosinate ammonium negatively affect human sperm mitochondria respiration efficiency

The widespread cultivation of genetically modified organisms (GMOs) led to a widespread use of selective herbicides to which GMOs are resistant, thus increasing the concern about human exposure to them. Glyphosate (GLY) and glufosinate ammonium (GA), the active principles of the main formulations, have been investigated for their effects on human health, mainly cancer and reproductive toxicity. However, little is known about their effects on the molecular mechanisms related to sperm quality.To investigate the effects of GLY and GA on mitochondrial respiration efficiency, we took advantage of our already established ex vivo human sperm mitochondria assay. Since spermatozoa are highly regulated by sex steroids, we tested at first testosterone (T), di-hydroxytestosterone (DHT), 17β-estradiol (E2) and progesterone (P4). Then, we tested the effects of GLY and GA and of the hormone-like flavonoid quercetin (QRC) in a dose-dependent manner. The 0.1−1000 nM concentration range has been considered because it covers both the sexual hormones physiologically relevant concentrations (10 nM), triggering endogenously hormone-dependent signaling pathways, and the estimated (nM range) QRC dietary intake. Subsequently, co-incubation experiments were carried out with the two herbicides in the presence of 10 nM of each sex steroid and QRC.We found that: i) DHT and QRC are able to significantly reduce mitochondrial functionality at concentrations ≥ 10 nM; ii) GLY and GA negatively affect mitochondrial respiration efficiency; iii) in the presence of 10 nM DHT, the negative effect of GLY was increased; iiii) DHT, QRC and GA target mitochondria by using a mechanism different from GLY.

Seeding is not always necessary to restore native early successional plant communities

Restoration of native early successional plant communities in the eastern United States is a conservation priority because of declining populations of associated plants and wildlife. Restoration typically involves seeding native species and is often fraught with problems including weedy competition, expensive seed, and slow establishment. Pairing seed bank response with strategic herbicide applications may be an alternative approach for restoring these plant communities. We compared early successional plant communities established by seeding (SD) paired with selective herbicide use to natural revegetation (NR) from the seed bank paired with selective herbicide use at 18 locations that were previously row‐crop or tall fescue (Schedonorus arundinaceus) fields in Tennessee, Alabama, and Kentucky, the United States. We did not detect differences in species diversity and richness, coverage of non‐native grasses and forbs, or number and coverage of native flowering forbs by season between NR and SD treatments at tall fescue or fallow crop sites. Species evenness was greatest in NR and coverage of native‐warm‐season grasses in SD. Species richness and coverage of native forbs were least in untreated tall fescue units (CNTL). More flexibility to use herbicides with NR reduced coverage of sericea lespedeza (Lespedeza cuneata) in NR units compared to SD units at tall fescue sites. NR was 3.7 times cheaper than seeding. Land managers should consider using an NR approach to establish native early successional plant communities.

Selectivity of Saflufenacil Applied Alone or Mixed to Glyphosate in Maize

The use of selective herbicides is important for weed management in agricultural crops. Selectivity studies of new molecules are really important to expand the control options of glyphosate-resistant and -tolerant eudicotyledons in corn. The objective of this work was to evaluate the selectivity of the herbicide saflufenacil applied alone in different doses in post-emergence of corn and in a mixture with glyphosate. The design used was randomized blocks, with four replications, with treatments consisting of five doses of saflufenacil, applied alone and in a mixture with a fixed dose of glyphosate, in addition to the weeded control and only glyphosate. At 7, 14, 21 and 28 days after application (DAT), the phytotoxicity of the herbicides to the crop was evaluated. The physiological variables were measured at 35 DAT. At harvest, yield components were determined, in addition to the mass of 1,000 grains and grain yield. The application of the mixture of glyphosate with saflufenacil increases phytotoxicity symptoms and yield losses. Doses of up to 70 g ha-1, applied alone, caused low phytotoxicity to corn and did not interfere in yield. The use of glyphosate + saflufenacil tank mixtures caused decreases in yield of 43.96 and 40.81% when compared, respectively, with the weeded control and the averages of the applications of the herbicides alone. Saflufenacil has the potential to be used in the management of eudicotyledonous weeds, as long as it is not mixed with glyphosate and the dose limit is respected.

Analysing the importance of glyphosate as part of agricultural strategies: A discrete choice experiment

The use of glyphosate plays an important role in farmers’ strategic decisions for reducing weed pressure and yield losses. In this paper, the use of glyphosate is analyzed as part of a complete agronomic strategy in which the farmer has to choose between the use of a combination of mechanical and chemical weed control. A special aim was to analyze the trade-off in the farmers’ preferences between a cultivation strategy with or without glyphosate. The empirical analysis is based on a discrete choice experiment with 328 German farmers. It was found that after the harvest of rapeseed, farmers have no clear preference for the use of glyphosate in a mulch seeding strategy. However, the preference for glyphosate use is affected by the weed pressure and the presence of specific weeds. While the farmers’ risk attitude has no influence on the decision to use glyphosate, we observed an increasing preference for its use on larger farms. Furthermore, our results reveal that farmers prefer mechanical weed control in pre-sowing instead of the use of selective herbicides in pre- or post-emergence. This preference increases if weed resistance is an issue on the farm. Potential yield impacts caused by glyphosate use show that yield losses have a higher impact on the farmers’ decision than yield gains. We conclude that farmers prefer the use of glyphosate to other alternatives as it is an important part of their agronomic strategy to prevent weed infestation and save work and labour costs, especially on large farms.

Assessing the efficacy and impact of management of an invasive species in a protected area: Poa annua on sub‐Antarctic Macquarie Island

SummaryPlant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub‐Antarctic temperatures and their off‐target impacts may increase eradication success. With interest in controlling non‐native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub‐Antarctic biotype) in sub‐Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub‐Antarctic Macquarie Island through field‐based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub‐Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one‐off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow‐up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site‐specific testing of control methods and understanding off‐target impacts of control when managing alien plant species in protected areas.

Mowing Effects on Woody Stem Density and Woody and Herbaceous Vegetation Heights Along Mississippi Highway Right-of-Ways

Abstract Roadside right-of-ways (ROWs) undergo regular disturbances such as mowing, maintenance, wrecks, and road developments, which affect soils, groundwater, surface hydrology, and the composition of vegetation. Roadsides can provide and support an environment for diverse plant communities, but management practices have reduced native grasses, wildflowers, and woody plants. Woody plants are not desirable for traffic safety, maintenance, and visibility along road ROWs. Therefore, the objectives of this study were to investigate effects of roadside mowing frequency on native and nonnative herbaceous and woody plant vertical height coverage and native and nonnative woody stem density within plant communities along highway ROWs. We subdivided 10 research plots, systematically situated along Highway 25 in Oktibbeha and Winston counties, Mississippi, to receive 1) four or more mowings annually, 2) one mowing during fall, and 3) one mowing during fall with supplemental native wildflower seeding. We differentiated upland plots on the basis of soil drainage in upward hills. Riparian (lowland) areas were influenced by overbank inundations from streams and drainages, and were typically spanned by bridges or box culverts. We used line transects to sample vegetation. We detected 277 plant species, including native and nonnative forbs, legumes, grasses, rushes, sedges, and woody perennials (vines, shrubs, and trees). Nonnative grasses exhibited the greatest percent coverage (>90%) in all treatments. Woody plants, including vines, trees, and shrubs, comprised <8% coverage throughout the study. Percent coverage of all vegetation in different height categories differed between upland and riparian elevations (F1,59 > 4.65, P ≤ 0.04), seasons (F1,59 > 12.78, P ≤ 0.01), and between years (F1,59 > 4.91, P ≤ 0.03), but did not differ in height categories among treatments. Of the <8% coverage of woody plants, woody vines comprised most (>68%) of the stem counts, whereas 24% were trees and <8% were shrubs. Woody stem density did not differ among treatments or seasons, but between elevations (F1,59 = 3.34, P = 0.07) and during the 2-y study (F1,59 = 3.21, P = 0.08) as the trend was in the predicted direction (α = 0.05). Thickets of woody vines and low-lying trees and shrubs along the roadside ROWs did not compromise height requirements needed for roadside visibility and safety. At least one mowing per year would be needed to control tree and shrub species for visibility along roadside ROWs. We concluded that a 2-y mowing regimen was no different from mowing once annually and/or more than three times annually in the plant communities in east-central Mississippi. However, one mowing/y retained agronomic plant coverage, which is useful for erosion control and soil stabilization during roadside maintenance. Proactive management implementations can include native plantings, selective herbicide use to decrease nonnatives, continual mowing from roadside edge to 10 m, and only one mowing in late fall with an extension of the boundary to reach beyond 10 m from the roadside edge to suppress invasion of woody plants. Adopting this less-frequent mowing regimen could reduce long-term maintenance costs for Mississippi highways.

Patterns of pre-crop glyphosate use and in-crop selective herbicide intensities in Northern Germany

Abstract We present a detailed analysis of glyphosate-based herbicide (GBH) use patterns with a dataset of herbicide use on arable farms in five districts of Northern Germany. Two aspects are focused: (1) The relationship between GBH and selective herbicides used on a specific field in the same cropping period and (2) the interplay of tillage, GBH and selective herbicide use in weed management. The most interesting result of our analysis is that the intensity of selective herbicide use for in-crop weed management was not related to GBH treatment prior to the crop (except maize). GBH treatments increased the total herbicide intensity on a field. Hence, using GBH pre-crop does not necessarily save herbicides in the following crop. GBH were additional treatments, not replacing selective herbicides. Our data was collected from different districts in Northern Germany extending from West to East. In the Eastern districts, a larger proportion of fields were treated with GBH. When a field was treated with GBH, it was applied with a similar intensity, regardless of the district. Hence, differences in GBH use patterns were caused only by the decision to treat pre-crop, while the intensity of these GBH treatments is hardly varied. In the Eastern districts, the higher proportion of fields treated with GBH is associated with larger proportion of fields with non-plough tillage. Non-plough fields were also treated more intensively with selective herbicides. Nevertheless, the use of both GBH and selective herbicides on the same field was more frequent and intensive in the Western districts of Northern Germany. We attribute the differences in pre-crop GBH use and in-crop selective herbicide use to regional production differences. Small to medium proportions of fields with both ploughing for primary tillage and pre-crop GBH use in all districts and most prominent in winter barley, winter wheat and maize indicate a luxurious, easy reducible use of GBH. We propose to promote farms with non- and low-use of GBH as an example of good practice.

Impacts of tillage and herbicide mixture on weed interference, agronomic productivity and profitability of a maize – Wheat system in the North-western Indo-Gangetic Plains

Weeds comprising of annual monocotyledons, dicotyledons and perennial Cyperus rotundus L. (hereafter referred to as nutsedge) are important constraints in maize-wheat production system in India. They can cause yield losses of 25–30% in maize and 10–25% in wheat. Recently, continuous use of selective herbicides has led to an increase of nutsedge and other annual weeds in maize. There is need for a broad-spectrum weed control strategy that includes control of nutsedge in maize. Herbicide mixtures, containing a nutsedge killer partner herbicide may prove to be more effective for this. Imazethapyr among herbicides available in India possesses nutsedge-killing action, but the tolerance of maize to this herbicide, which is usually recommended for application as post-emergence in soybean and groundnut, is variable. We observed dose-dependent selectivity/tolerance of maize to imazethapyr when applied as post-emergence in a previous trial. Imazethapyr’s pre-emergence application may prove more useful in offering selectivity to maize, but is hardly studied. In addition, its residual/carry-over effect may lead to weed control in following wheat crops grown in sequence with maize, economizing production costs of the maize-wheat system. Therefore, this experiment was designed to evaluate the efficacy of imazethapyr against weeds including nutsedge, and its selectivity in maize crops when applied as pre-emergence in tank-mixture with pendimethalin; to compare these tank-mixtures effects with that of the sequential applications of pendimethalin (pre-emergence) and imazethapyr (post-emergence) in maize; and to evaluate their residual actions combined with tillage and crop residue in wheat under a maize- wheat system. The application of pre-emergence tank-mixture of pendimethalin 0.75 kg a.i. ha−1 + imazethapyr 0.050 kg a.i. ha−1 caused significant reductions in densities of broad-leaved (30%), nutsedge (45.2%), grassy (79.7%) and total weeds (49.1%) compared with un-weeded control (UWC) in maize. It reduced total weed dry weight by 58.3% and gave 56.1% higher maize yields than UWC. Among the tillage treatments adopted in the wheat crop, zero tillage (ZT) + residue (R) resulted in 14.0% greater reductions in weed dry weight and 6.9% higher wheat yields than conventional tillage (CT). It increased maize-wheat system productivity by 5.4% and 7%, respectively over CT and ZT without residue. The application of a tank-mixture of pendimethalin + imazethapyr gave 2.9% lower system productivity, but 8.2% higher net returns than the weed-free control, reducing the weed seed bank by 65% at 0–15 cm soil layer in two years. The application of this tank-mixture (in maize), followed by ZT + residue (in wheat) was more remunerative and could lead to better weed control with 25% and 50% lower doses of pendimethalin and imazethapyr, respectively, and 50% reduction in application cost. This practice can be adopted in maize-wheat system under irrigated conditions in the North-western Indo-Gangetic Plains of India, and in similar agro-ecologies of the tropics and sub-tropics. This result can also be applicable to cropping systems like maize – mustard, maize – barley/oat, subject to further evaluation and refinement under field conditions.

Seletividade de herbicidas aplicados em pré e pós-emergência da cultura do cártamo

O cultivo do cártamo tem aumentado nos últimos anos, principalmente para a produção de biodiesel. O controle de plantas daninhas a fim de evitar perdas na produtividade da cultura faz se necessário. Desta forma, uma alternativa que surge é o uso de herbicidas seletivos para a cultura. Objetivou-se verificar a seletividade de herbicidas em pré e pós-emergência para a cultura do cártamo. Foram conduzidos dois experimentos adotando-se delineamento em blocos casualizados com quatro repetições. Para o primeiro experimento com aplicações em pré-emergência os tratamentos foram arranjados em esquema fatorial 6 x 2 + 1, enquanto que para o segundo experimento, com as aplicações em pós-emergência os tratamentos foram dispostos em esquema fatorial 7 x 2 + 1. Em ambos experimentos, o fator A correspondeu aos diferentes herbicidas e o fator B às doses utilizadas, e o tratamento adicional consistiu de testemunha sem aplicação de herbicidas. Foram realizadas avaliações visuais de fitointoxicação nas plantas aos 7, 14 e 21 dias após a aplicação, altura de plantas, estande e produtividade. Os herbicidas chlorimuron-ethyl (20 e 40 g i.a. ha-1), flumioxazin (50 e 100 g i.a. ha-1), imazaquin (161 e 322 g i.a. ha-1), s-metolachlor (1440 e 24000 g i.a. ha-1) e sulfentrazone (300 g i.a. ha-1), aplicados em pré-emergência, e os herbicidas sethoxydim (184 g i.a. ha-1), fluazifop-p-butyl (375 e 750 g i.a. ha-1) haloxyfop-methyl (60 e 120 g i.a. ha-1) e clethodim (108 g i.a. ha-1), aplicados em pós-emergência foram seletivos para a cultura do cártamo.

Evaluation of Mowing Frequency on Right-of-Way Plant Communities in Mississippi

AbstractNative grasses and native wildflowers are declining, especially along roadside right-of-ways because of intensive mowing and herbicide management practices. Roadside right-of-ways undergo regular disturbances such as mowing, maintenance, and road developments that affect soils, groundwater, surface hydrology, and vegetation composition. We investigated species richness and percent coverage within plant communities along highway right-of-ways to determine if reduced mowing increased native plant coverage. The study was conducted using 10 research plots situated along Highway 25 in Oktibbeha and Winston counties, Mississippi. Each research plot consisted of three different treatments as follows: one that included greater than four mowings per year, one mowing only in fall, and one mowing only in fall with a supplemental native wildflower seeding. Using line transect sampling, we detected 277 plant species, which included native and nonnative forbs, legumes, grasses, rushes, sedges, and woody perennials (vines, shrubs, and trees). Total percent coverage of native and nonnative plants within different growth form categories did not differ among treatments (F2,96 = 0.45, P = 0.83). However, coverage differed between uplands and lowlands (F1,96 = 18.22, P ≤ 0.001), between years (F1,96 = 14.54, P ≤ 0.001), between fall and spring seasons (F1,96 = 16.25, P ≤ 0.001), and interacted between years and seasons (F1,96 = 24.08, P ≤ 0.001) and seasons and elevations (F1,96 = 5.00, P ≤ 0.001). Nonnative agronomic grasses exhibited the greatest coverage (> 90%) in all treatments. Percent coverage of each plant growth form was greatest in lowlands. Our research showed an increase of native grasses and wildflower species along roadsides with a reduced mowing regimen. We concluded that the timing and intensity of mowing for the duration of our study had little effect on the species composition of plant communities. However, one mowing per year retained agronomic plant coverage for erosion control and soil stabilization during roadside maintenance. Specific proactive management implementations can include native plantings, selective herbicide use to decrease nonnative grasses, continual mowing from roadside edge to 10 m, and only one mowing in late fall, but with an extension of the boundary to reach beyond 10 m from the roadside edge to suppress the invasion of woody plants, which could lead to lower long-term maintenance costs.

PM 9/20 (1) Parthenium hysterophorus

PM 9/20 (1) <i>Parthenium hysterophorus</i>

Screening e dose-resposta de herbicidas à malva e juta

A produção de fibra de malva (Urena lobata) e de juta (Corchorus capsularis) é demandada pela indústria como matéria prima na produção de telas, cordas, capas de livro entre outras aplicações. O ciclo de produção desta fibra é uma atividade sustentável, pois usa recursos renováveis das várzeas do Rio Solimões no Amazonas. O manejo da cultura aliado ao controle de plantas daninhas são condições para as espécies expressarem o máximo potencial produtivo. O uso de herbicidas seletivos se constitui numa alternativa eficiente e economicamente viável a esta finalidade. O objetivo desta pesquisa foi avaliar a seletividade de herbicidas por meio de screening e a dose-resposta destes as duas espécies produtoras de fibras naturais. Dois experimentos foram conduzidos em casa de vegetação: o primeiro na forma de screening para avaliar herbicidas aplicados em pós-emergência como bentazon, clethodim, fluazifop-p-butil, fomesafen, linuron, oxyfluorfen e sulfentrazone nas doses recomendadas para outras culturas; e o segundo, os herbicidas clethodim e fluazifop-p-butil, que foram seletivos à juta e à malva, em 7 doses. Os herbicidas bentazon, linuron, fomesafen, oxyfluorfen e sulfentrazone causaram morte de todas as plantas, enquanto o clethodim e fluazifop-p-butil foram moderadamente fitotóxicos. As duas espécies foram mais tolerantes ao fluazifop-p-butil que ao clethodim.

Plant and Soil Consequences of Shrub Management in a Big Sagebrush-Dominated Rangeland Ecosystem

This study investigated plant and soil (organic carbon, SOC) responses to shrub management in western U.S. rangeland dominated by Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young). Plants and soils were sampled in 2009 from paired sets of treatments (mowing to 10 cm height, aerial herbicide application of Spike® 20P [tebuthiuron]) in Sandy and Loamy ecological sites. Plant responses to mowing were consistent for both ecological sites with 1) no effects on live, but three- to four-fold increases in dead, Wyoming big sagebrush plant density, 2) reduced height and cover of Wyoming big sagebrush, 3) increased cover of perennial grasses, and 4) no effects on bare ground. For soils, increased SOC did occur with herbicide application in the Loamy site for both the 0-5 cm (43% increase) and 5-15 cm (17% increase) soil depths, which corresponded to annual soil C sequestration rates of 0.16 and 0.14 Mg C ha-1 yr-1 for the 0-5 and 5-15 cm soil depths, respectively. Shrub management in Wyoming big sagebrush-dominated rangelands affects the plant component for two different ecological sites, whereas effects on SOC were observed only when density of live Wyoming big sagebrush plants was reduced through selective herbicide use.

Efeito da aplicação de herbicidas dessecantes na soja sobre as populações de nematoides no solo

The use of herbicides is the main method of weed control in soybeans. Desiccants are also being used routinely to anticipate the harvest and / or minimize the deterioration of seed quality. There is the possibility of direct or indirect contact with such pesticides, affect the community of nematodes in the soil. However, such effects and their magnitudes are yet to be clarified, especially in the case of selective herbicides. Thus, the objective of this study was to evaluate the use of selective herbicides in soybean on nematodes harmful to the crop. The experiment was conducted with transgenic soybean (‘M-SOY 7908RR’). The experimental design was a randomized block design with the following treatments: paraquat (400 g a.i ha-1), diquat (200 g a.i ha-1), a mixture of paraquat and diquat (300 + 150 g a.i ha-1), two doses of carfentrazone ethyl (20 g a.i ha-1 and 30 g a.i ha-1) and control (without desiccant application). The nematode community in the area was monitored in four periods. In none of those was found significant variation in the populations of nematodes harmful to soybeans, due to the application of any of desiccants. However, especially in the last sampling time, the desiccant application always resulted in increased populations of free-living nematodes and parasites those considered weak for soybean.

Efeito da aplicação de herbicidas dessecantes na soja sobre as populações de nematoides no solo

The use of herbicides is the main method of weed control in soybeans. Desiccants are also being used routinely to anticipate the harvest and / or minimize the deterioration of seed quality. There is the possibility of direct or indirect contact with such pesticides, affect the community of nematodes in the soil. However, such effects and their magnitudes are yet to be clarified, especially in the case of selective herbicides. Thus, the objective of this study was to evaluate the use of selective herbicides in soybean on nematodes harmful to the crop. The experiment was conducted with transgenic soybean (‘M-SOY 7908RR’). The experimental design was a randomized block design with the following treatments: paraquat (400 g a.i ha-1), diquat (200 g a.i ha-1), a mixture of paraquat and diquat (300 + 150 g a.i ha-1), two doses of carfentrazone ethyl (20 g a.i ha-1 and 30 g a.i ha-1) and control (without desiccant application). The nematode community in the area was monitored in four periods. In none of those was found significant variation in the populations of nematodes harmful to soybeans, due to the application of any of desiccants. However, especially in the last sampling time, the desiccant application always resulted in increased populations of free-living nematodes and parasites those considered weak for soybean.

Field sprayer for inter and intra-row weed control: performance and labor savings

Studies of new tools and methods for weed control have been motivated by increased consumer demand for organic produce, consumer and regulatory demands for a reduction in environmentally harmful herbicide use, and the decreased availability of farm workers willing to perform manual tasks, such as hand weeding. This study describes the performance of a new sprayer system for commercial production that integrates two herbicide applications in a single pass, selective herbicide (SH) application in narrow bands over the crop row, and a non-selective herbicide (NSH) application between crop rows. A real-time kinematic (RTK) global positioning system (GPS) was used for auto-guidance in seeding and spraying operations. Conventional broadcast SHs and experimental treatments were applied at a constant nominal speed of 5.5 km h-1 for comparison. Trials in commercial sugar beet fields demonstrated the following: (i) average hand-weeding time can be reduced by 53% (ii) the new sprayer system reduced SH use by 76%, and (iii) sugar beet density did not change significantly during treatment. These results demonstrate the feasibility of using the new RTK-GPS controller sprayer system for differential and efficient herbicide application in inter- and intra-row zones in row crop production.

Herbicides to control poisonous Pimelea species (Thymelaeaceae)

Pimelea poisoning is an ongoing, periodically serious problem for cattle producers in inland Australia. The annual native plants of the Thymelaeaceae family that cause the problem are widespread and animal management is currently the main means of minimizing poisoning. However, there are situations in the higher rainfall parts of the natural distribution area of these plants where farming and quite intensive property development do occur and here the use of selective herbicides may be an option. This research looked for herbicides that could be considered for registration for Pimelea control, bearing in mind the large potential costs involved if used over large areas. Group I hormone herbicides (for example 2,4-D) were quite effective as was metsulfuron-methyl and glyphosate at doses commonly registered for use on broad-leafed weeds. On the basis of minimizing costs and quickly suppressing seed-set, metsulfuron-methyl at 3.5–5 g a.i. ha −1 and 2,4-D at 375–500 g a.i. ha −1 were the most promising. Where medic ( Medicago spp.) persistence is vital, 2,4-DB at 240–300 g a.i. ha −1 could be used and glyphosate at 1 kg a.i. ha −1 would be effective on fallowed ground if cost was not an over-riding concern.