Application Of Clethodim Research Articles

Assessing clethodim spot spraying applications for control of problematic weedy rice and other grasses in California rice fields

AbstractSpot spraying applications offer the opportunity to target specific weeds in a field, while simultaneously reducing herbicide usage and increasing the long‐term efficacy of chemical control options. The study is focused on controlling California weedy rice accessions (Oryza spp.) and problematic grass weeds with a spot spray application of clethodim in a flooded rice system. The efficacy of incorporating nonionic surfactant to clethodim applications was also assessed. Dose‐response experiments were carried out in a greenhouse on five weedy rice accessions, common grass rice weeds, and cultivated rice varieties L207, M105, M206, M209, M211, and S102 to determine the dose needed to affect these populations. Clethodim was applied in a field setting to assess spot spraying efficacy, the possibility of herbicide dispersion in the water, and crop injury. Clethodim successfully controlled weedy rice and grasses in the greenhouse. The effective rates to control 90% of the five test populations (ED90) were between 51 and 74 g ai ha−1 clethodim for weedy rice accessions. Adding nonionic surfactant to clethodim increased its efficacy by 1.6‐ to 1.9‐fold. Cultivated rice varieties did not exhibit any tolerance to clethodim, however, spot spraying applications at 150 g ai ha−1 clethodim did not cause any dispersion in the field. Clethodim spot spray application was effective both at the three‐ to four‐leaf growth stage and tillering growth stage for weedy rice.

Reduction in the Use of Some Herbicides Favors Nitrogen Fixation Efficiency in Phaseolus vulgaris and Medicago sativa.

In recent decades, the quality of agricultural soils has been seriously affected by the excessive application of pesticides, with herbicides being one of the most abundant. Continuous use of herbicides alters the soil microbial community and beneficial interactions between plants and bacteria such as legume-rhizobia spp. symbiosis, causing a decrease in the biological nitrogen fixation, which is essential for soil fertility. Therefore, the aim of this work was to study the effect of two commonly used herbicides (pendimethalin and clethodim) on the legume-rhizobia spp. symbiosis to improve the effectiveness of this process. Phaseolus vulgaris plants grown in pots with a mixture of soil:perlite (3:1 v/v), showed a 44% inhibition of nitrogen fixation rate with pendimethalin. However, clethodim, specifically used against monocots, did not induce significant differences. Additionally, we analyzed the effect of herbicides on root exudate composition, detecting alterations that might be interfering with the symbiosis establishment. In order to assess the effect of the herbicides at the early nodulation steps, nodulation kinetics in Medicago sativa plants inoculated with Sinorhizobium meliloti were performed. Clethodim caused a 30% reduction in nodulation while pendimethalin totally inhibited nodulation, producing a reduction in bacterial growth and motility as well. In conclusion, pendimethalin and clethodim application reduced the capacity of Phaseolus vulgaris and Medicago sativa to fix nitrogen by inhibiting root growth and modifying root exudate composition as well as bacterial fitness. Thus, a reduction in the use of these herbicides in these crops should be addressed to favor a state of natural fertilization of the soil through greater efficiency of leguminous crops.

ACCase inhibitor fractionation and glyphosate addition improve perennial sourgrass control

Glyphosate-resistant sourgrass is difficult to control, particularly when perennial, and strategies that improve the control efficiency against this grass and preserve the useful life of graminicides are warranted. Therefore, the present study aimed to answer the following questions: (i) Does fractionating the doses of ACCase inhibitors improve the control of perennial sourgrass? (ii) Does alternating the chemical groups cyclohexanediones (DIMs) and aryloxyphenoxypropanoates (FOPs) improve the control of perennial sourgrass, and does the order of their application affect sourgrass control efficiency? (iii) Does the addition of glyphosate to ACCase inhibitors improve to the control of perennial sourgrass resistant to 5-enol-pyruvyl-shiquime-3-phosphate synthase inhibitors? Two field experiments (I and II) were performed in 2018 and repeated in 2019. In experiment I, the treatments included a single or fractional application clethodim + quizalofop-P-ethyl (216 + 108 g a.i. ha-1), clethodim (216 g a.i. ha-1), and quizalofop-P-tefuryl (108 g a.i. ha-1), applied in the order of clethodim followed by quizalofop-P-tefuryl and vice versa, as well as a control treatment. In experiment II, the treatments included a single or fractional application of clethodim + quizalofop-P-ethyl (216 + 108 g a.i. ha-1) and clethodim (108 g a.i. ha-1), isolated or associated with glyphosate, as well as a control treatment. In both experiments, the interval between the fractional applications was 7 days. Percentage of control, number of tillers per plant, and height of sourgrass plants were determined. Compared with the unfractionated application, the fractionation of clethodim + quizalofop-P-ethyl and clethodim increased control by respectively 20-24 and 25-30%. Fractionated clethodim has greater

Efficacy of Burndown with Sequential Applications for Junglerice (Echinochloa colona) Control

Junglerice has continued to expand its range as a serious weed pest in Tennessee cotton. Both glyphosate resistance and herbicide antagonism have been documented as possible causes for poor control. Approximately 15% of junglerice populations in Tennessee have been found to be glyphosate resistant. In addition, dicamba tank mixtures with glyphosate and/or clethodim have been reported to reduce junglerice control. Due to poor in-crop control, starting clean has taken on added importance when trying to control junglerice. Therefore, research was conducted to determine the best herbicide burndown methods utilizing clethodim, dicamba, glufosinate, glyphosate, or paraquat. Paraquat alone or in tank-mixtures with glyphosate or clethodim provided poor control (< 50%). Likewise, glufosinate alone or in tank-mixture with glyphosate or clethodim provided poor control (< 35%). A dicamba + glyphosate, glufosinate + clethodim, or paraquat + clethodim application provided poor junglerice control. Regardless of which herbicides were initially applied, making a follow-up application of glyphosate or glyphosate + clethodim two weeks later provided optimal control of junglerice. In Tennessee, a glyphosate + clethodim application at 14 days before planting is recommended to control junglerice, other grasses and some broadleaf weeds, followed by paraquat at-planting to control remaining weed species.

Differences in biological efficiency of one- and two-component graminicide on sugar beet crops in Tula region

One of the most urgent tasks in sugar beet production for Russia today is irregularities in cultivation technology and a low-efficiency crop protection. It leads to a high level of weed infestation of agricultural fields. Developing and identifying the most efficient, selective and accessible herbicides, which have low phytotoxicity, do not have a negative effect on soil chemical characteristics and can be used in sugar beet cultivation is relevant today. The aim of this study was to examine and compare biological efficiency of various doses and concentrations of one- and two-component graminicides on sugar beet crops against the following weeds: Cockspur grass Echinochloa crusgalli (L.) Beauv., Wild millet Setaria glauca (L.) Beauv. and Couch Grass Elytrigia repens (L.) Nevski. The experiment was conducted on the territory of the Tula region in 2020. The total field experiment area was 480 m2. Application of clethodim + quizalofop-P-ethyl (0.5 l/ha) resulted in reducing the number and weight of annual weeds by 6471 %, reducing the number and weight of perennial weeds by 5458 %, which had the same efficiency as clethodim (0.6 l/ha). The efficiency of clethodim + quizalofop-P-ethyl (1.0 l/ha) was higher than Clethodim (0.6 l/ha) and amounted to 7387 % of reduction in the number of weeds compared to the control, but was lower than Clethodim (1.8 l/ha), which resulted in 8995 % reduction in the number of weeds compared to the control. The highest sugar beet yields were obtained in the variants with clethodim (1.8 l/ha) and two-component herbicide (1 l/ha), which amounted to 28 and 25 % yield increase, in comparison with the control.

Efeito residual de clethodim aplicado em pré-semeadura do milho

O Brasil é um dos poucos países onde é possível realizar mais de uma safra no mesmo ano agrícola, sendo a sucessão soja-milho praticada por grande parte dos produtores. Este sistema cultural proporcionou a seleção de plantas daninhas resistentes à herbicidas, principalmente pela utilização de herbicidas com mesmo mecanismo de ação em sucessivos cultivos. Neste cenário, novas estratégias de manejo devem ser adotadas, como aplicações de herbicidas em pré-semeadura do milho. O objetivo deste trabalho foi avaliar a influência de períodos de aplicação de clethodim em pré-semeadura, sobre a emergência e desenvolvimento inicial de híbridos de milho. Para tal, avaliou-se o efeito residual de clethodim sobre híbridos 2B810 Power Core, Status Viptera 3, Dekalb 340 VT PRO2 com aplicação de clethodim 196,80 g L-1 i.a. aos 15, 10, 5, 3 e 1 dias antecedendo a semeadura (DAS) do milho e uma testemunha sem aplicação. As variáveis analisadas foram: emergência, altura de plantas, índice de clorofila falker, diâmetro de colmo, acúmulo de matéria fresca e seca. A aplicação de clethodim 1 dia antecedendo a semeadura afetou negativamente a emergência e o desenvolvimento inicial dos híbridos de milho avaliados. Os híbridos apresentaram suscetibilidade diferencial ao residual de clethodim para as variáveis emergência, acúmulo de matéria fresca e acúmulo de matéria seca.

Impact of Late‐Season Herbicide Applications on Winter Canola Yield and Seed Quality

Core Ideas The application of glyphosate during early reproductive growth resulted in significant declines in yield. Decreased yields with late‐season herbicides were associated with an increased number of aborted pods; however, this may not be the only factor contributing to the yield decline. Seed oil content followed the same general trend as grain yield, with decreased oil yields when glyphosate was applied during early reproductive growth. In canola (Brassica napus L.), control of grassy weeds can typically be achieved in the fall or spring with timely herbicide applications. However, environmental conditions can delay these applications into canola reproductive growth stages, which have an unknown effect on canola productivity. Therefore, a study was conducted to determine the impact of late‐season herbicide applications on canola grain yields and seed quality. The impact of three herbicides (glyphosate [N‐(phosphonomethyl)glycine], clethodim [(E)‐2‐[1‐[[3‐chloro‐2‐propenyl)oxy]imino]propyl]5=[2‐(ethylthio)propyl]‐2‐hydroxy‐2‐cyclohexen‐1‐one], and quizalofop‐P‐ethyl [Ethyl(R)‐2‐[4‐(6‐chloroquinoxalin‐2‐yloxy)‐phenoxy]propionate]) and three applications timings (bolting, early flower, and mid‐flower) were investigated on winter canola from 2015 through 2018 in Perkins and Stillwater, OK. Grain yields and pod abortion were collected at maturity. Subsamples of harvested seed were collected from each plot and used for oil analysis. When averaged across years, the application of glyphosate at bolting and early flower resulted in yield decreases of 531 and 488 kg ha–1 compared with the nontreated control. Yield following the application of clethodim at early flower resulted in a 185 kg ha–1 (2017) and 280 (2018) kg ha–1 decrease in yields compared with the control. Although yield decreases were observed following a few treatments, a significant increase in pod abortion was noted following many herbicide treatments, indicating that pod abortion was not the only factor contributing to yield declines. Decreases in oil content were only found following glyphosate applications at bolting and early flower. These results indicate that late‐season herbicide applications, especially glyphosate, should be avoided in winter canola.

Off-Target Impacts of Graminoid-Specific Herbicide on Common Camas (Camassia quamash) Growth, Abundance, Reproduction, and Palatability to Herbivores

Invasive grass removal with herbicide is an important component of the restoration process in many prairie and grassland ecosystems. Management of invasive grasses in areas with high concentrations of native plants necessitates investigation of off-target herbicide effects on sensitive native species. Two graminoid-specific herbicides, Fusilade (active ingredient fluazifop-P-butyl) and Envoy Plus (active ingredient clethodim), are frequently used to control invading broadleaf pasture grasses in Pacific Northwest prairies with little knowledge of how these chemicals impact native plants. One such native plant, common camas (Camassia quamash), is a characteristic forb of these prairies that often grows in areas treated with these herbicides. Because camas is a critical resource for native pollinators and holds ethnoecological significance to native peoples, it is important that management methods do not negatively impact this plant. The objective of this study was to understand if and how various seasonal applications of clethodim and fluazifop may impact camas. We implemented a factorial design testing the effects of herbicide type (fluazifop, clethodim, control) and application season-frequency (combinations of mid-spring, late-spring, fall) on camas growth, foliar cover, reproduction, and palatability to herbivores. Our results show that herbicide treatments may reduce leaf length and increase flower and seed production, but do not influence seed viability or palatability to herbivores. The observed effects are not likely to be ecologically detrimental, suggesting that repeat applications of either fluazifop or clethodim can be safely used in areas with high concentrations of this iconic prairie species.

Frost Reduces Clethodim Efficacy in Clethodim-Resistant Rigid Ryegrass (Lolium rigidum) Populations

Rigid ryegrass, an important annual weed species in cropping regions of southern Australia, has evolved resistance to 11 major groups of herbicides. Dose–response studies were conducted to determine response of three clethodim-resistant populations and one clethodim-susceptible population of rigid ryegrass to three different frost treatments (−2 C). Clethodim-resistant and -susceptible plants were exposed to frost in a frost chamber from 4:00 P.M. to 8:00 A.M. for three nights before or after clethodim application and were compared with plants not exposed to frost. A reduction in the level of clethodim efficacy was observed in resistant populations when plants were exposed to frost for three nights before or after clethodim application. In the highly resistant populations, the survival percentage and LD50were higher when plants were exposed to frost before clethodim application compared with frost after clethodim application. However, frost treatment did not influence clethodim efficacy of the susceptible population. Sequencing of the acetyl coenzyme A carboxylase (ACCase) gene of the three resistant populations identified three known mutations at positions 1781, 2041, and 2078. However, most individuals in the highly resistant populations did not contain any known mutation in ACCase, suggesting the resistance mechanism was a nontarget site. The effect of frost on clethodim efficacy in resistant plants may be an outcome of the interaction between frost and the clethodim resistance mechanism(s) present.

Geographic Distribution of Ryegrass Resistent to the Clethodim Herbicide in Rio Grande do Sul1

ABSTRACT Ryegrass is a weed of annual cycle that is present in winter crops, in orchards and vineyards of the South region of Brazil. The species is normally controlled by the glyphosate herbicide, but the continuous use of this product caused the selection of resistant biotypes. The use of ACCase inhibitor herbicides is the main alternative for the control of this species, but it has not been satisfactory in some places, thus causing suspicion of resistance to this action mechanism. Thus, the objective of this paper was to evaluate the occurrence and geographic distribution of ryegrass biotypes that are resistant to the clethodim herbicide in the state of Rio Grande do Sul. For that, seeds of ryegrass plants that survived the application of clethodim were collected in crops from the north region of RS, summing up to a total of 152 samples from 72 cities. The biotypes were submitted to the application of 120 g i.a. ha-1 (maximum registered dose) and 60 g i.a. ha-1 de clethodim (half the maximum registered dose). According to the results, among the samples of ryegrass seeds collected, there were no biotypes resistant to the clethodim herbicide when the maximum registered dose was applied and in the stage of three to four leaves. However, there were biotypes with lower susceptibility that survived half the maximum registered dose.

Interferência e controle de milho voluntário tolerante ao glifosato na cultura da soja

Resumo: O objetivo deste trabalho foi estimar o efeito da infestação de milho voluntário tolerante ao glifosato na produtividade da cultura da soja, bem como avaliar o controle dessas plantas com o herbicida cletodim. Seis experimentos foram desenvolvidos, na safra de 2013/2014, nos estados da Bahia, de Minas Gerais, de Mato Grosso, do Paraná, do Rio Grande do Sul e de São Paulo. Espigas de milho sem palha, segmentadas ao meio, foram uniformemente distribuídas nas parcelas, à densidade de 1, 2 ou 4 segmentos por metro quadrado. Como tratamento herbicida, utilizou-se cletodim, nas seguintes doses: aplicação única, 108 g ha-1, sobre a soja com três trifólios (3T); aplicação única, 108 g ha-1, sobre soja com seis trifólios (6T); e duas aplicações, 108 e 84 g ha-1, sobre soja nos estágios 3T e 6T. Adicionou-se, ainda, um tratamento com a soja plenamente capinada. O aumento de densidade dos segmentos de espiga reduziu a produtividade da soja em até 69,9%. A produtividade da soja foi assegurada com o controle eficaz das plantas voluntárias de milho tolerante ao glifosato, oriundas de espigas, em aplicação única de cletodim (108 g ha-1) no estádio 6T; ou por meio de duas aplicações sequenciais do graminicida, com a soja em 3T e 6T.

Impact of glyphosate-resistant volunteer corn (Zea mays L.) density, control timing, and late-season emergence on yield of glyphosate-resistant soybean (Glycine max L.)

Glyphosate-resistant (GR) volunteer corn is a troublesome weed in soybean fields in a corn-soybean rotation as well as in corn fields in a continuous corn production system. The objectives of this study were to evaluate the impact of (1) different densities of GR volunteer corn on soybean yields, present as individual plants or clumps, controlled at fourth trifoliate (V4), sixth trifoliate (V6), or full flowering (R2) soybean growth stages, and (2) late-season volunteer corn emergence on soybean yields, after being controlled at different soybean growth stages. Field experiments were conducted in 2013 and 2014 under irrigated conditions in Clay County, Nebraska, and under rain-fed conditions in Lancaster County, Nebraska, USA. To maintain the desired number of isolated volunteer corn plants (1250, 2500, 5000, and 10,000 plants ha−1) and clumps (63, 125, 250, and 500 clumps ha−1), individual seeds and/or corn ears were hand-planted in each plot based on their respective target densities. Volunteer corn was controlled with applications of clethodim at V4, V6, or R2 soybean growth stages. Late-season volunteer corn emergence had no effect on soybean yield with volunteer corn densities and control timings at both locations in 2013 and 2014. During the first year of study at Clay County, volunteer corn densities and control timings had no effect on soybean yield. When volunteer corn was left uncontrolled or controlled at the R2 soybean growth stage, yield was the lowest at highest isolated volunteer corn plants (10,000 plants ha−1) plus clump density (500 clumps ha−1) during the second year of study in Clay County (≤5068 kg ha−1) and during both years of study in Lancaster County (≤1968 kg ha−1).

Establishing Legumes in a Tall Fescue Sward

Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] is a common grass species in the eastern half of the USA, but legumes grown with it could provide benefits. Obstacles to legume establishment in fescue pastures include disease, insect damage, and grass competition. Experiments were performed in 2010 and 2011 at Site 1 to test the efficacy of insect control, disease control, and two methods of grass suppression on seedling establishment of three legumes. The highest seedling density of red clover (Trifolium pretense L.) was obtained with glyphosate treatment regardless of pest control and for clipping without pest control. No overall or consistent benefit was found for white clover (Trifolium pretense L.) or trefoil (Lotus corniculatus L.) from seed and foliar insecticides or fungicides, or for grass suppression by either clipping or glyphosate application. Experiments were performed in 2012 and 2013 at Site 2 to test the efficacy of grass suppression by grazing cattle or by clethodim application. Seedling density of red clover was not significantly improved by either treatment, but the density of birdsfoot trefoil was increased by clethodim, and the density of white clover was increased in 2013 by both methods of grass suppression. Overall, red clover was least sensitive to grass competition. Birdsfoot trefoil was better served by the immediate effect of chemical suppression, whereas white clover benefitted most from the lengthier grass suppression provided by grazing.

Influence of Clethodim Application Timing on Control of Volunteer Corn in Soybean

Herbicide options for management of volunteer corn in soybean include a variety of acetyl CoA carboxylase-inhibiting herbicides, yet often, applications of acetyl CoA carboxylase herbicides are delayed until the weed is visible above the soybean canopy. Volunteer corn growing above the soybean canopy is a highly competitive weed, and herbicides applied at this point can kill the weed, yet soybean yield loss is still a concern. Our objective was to compare the effect of controlling various densities of volunteer corn growing in soybean EARLY (≤ 30 cm) versus LATE (≈ 90 cm) on percent control and soybean yield. Seven volunteer corn densities (0, 0.5, 2, 4, 8, 12, and 16 plants m−2) were hand planted into 19-cm row soybean. Clethodim 79 g ai ha−1was tank-mixed with glyphosate at 840 g ae ha−1and applied to the volunteer corn EARLY and LATE. The EARLY application provided higher and less variable control of volunteer corn 14 d after treatment (DAT) compared to LATE applications at all volunteer corn densities. There was no difference in control at 28 DAT for both the EARLY and LATE applications. Soybean yield was not affected by either application timing. Although no yield reduction was seen with the LATE treatments, later-season applications of clethodim to control volunteer corn may offer more variable control and could allow for additional Bt selection pressure on targeted insect pests.

Estratégias para o controle de capim-amargoso (Digitaria insularis) resistente ao glyphosate na cultura milho safrinha

As características de agressividade do capim-amargoso (Digitaria insularis) e a existência de biótipos resistentes ao glyphosate colocam esta planta daninha em evidência no cenário agrícola brasileiro. Neste sentido, o trabalho teve como objetivo a avaliação de estratégias para o manejo de capim-amargoso (Digitaria insularis) resistente ao glyphosate na cultura do milho safrinha. A utilização paraquat na dessecação pré-colheita da soja seguida da aplicação de clethodim dois dias após a colheita da proporcionou a maior flexibilidade para a escolha dos herbicidas utilizados em pós-emergência do milho.

Herbicide Treatment and Timing for Controlling Kentucky Bluegrass (Poa pratensis) and Tall Fescue (Festuca arundinacea) in Cool Season Grasslands of Central Kentucky, USA

The goal of this study was to evaluate the efficacy of four herbicides for controlling invasive Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) in idle grasslands by monitoring post-treatment plant communities. Experiments were conducted in two remnant savannas in central Kentucky. With the exception of domestic grazing, these sites were chosen because they were undisturbed by agriculture and development. Single treatments of 0.2 kg ai/ha imazapic, 0.2 kg ai/ha clethodim, 0.2 kg ai/ha imazapic 1.1 kg ai/ha glyphosate, 0.03 kg ai/ha sulfosulfuron, and an untreated control were implemented in fall 2004 and spring and summer 2005 at each site in a randomized complete block design. Plant communities were monitored 3, 10, 12, 14, and 15 months after the final treatments were implemented. At 15 months post-treatment, tall fescue cover was reduced in all treatment plots relative to the untreated control, with the greatest reduction in tall fescue cover occurring in the summer treatment plots. Spring applications of each herbicide were more effective for Kentucky bluegrass control than summer or fall treatments. All herbicide treatments reduced Kentucky bluegrass compared to untreated plots. The most effective herbicide treatment was imazapic glyphosate, which reduced Kentucky bluegrass cover to less than 7%. However, the resulting bare ground facilitated invasions by other aggressive exotic species, notably musk thistle (Carduus nutans L.). Spring applications of clethodim reduced Kentucky bluegrass cover relative to the untreated plots, and resulted in the highest number of native plant species compared to all other plots. This conservation of forb cover provided by clethodim may be of importance in managing areas impaired by this aggressive, invasive grass.Nomenclature: Carduus nutans L., Clethodim, glyphosate, imazapic, Kentucky bluegrass, musk thistle, Poa pratensis L., sulfosulfuron, tall fescue

The negative effects of clethodim in photosynthesis and gas-exchange status of maize plants are ameliorated by salicylic acid pretreatment

In this work, the injuries caused by clethodim herbicide application as well as the use of exogenous salicylic acid (SA) as a protective agent against clethodim in Zea mays leaves were examined. Although the target for clethodim is the inhibition of acetyl coenzyme A carboxylase (ACCase) which is the key enzyme for fatty acid biosynthesis, it can indirectly affect the photosynthetic machinery, gaseous exchange and some biochemical parameters. Clethodim application caused chlorosis and yellowing of leaf-tip parts. Higher doses caused browning or reddening of leaves and sometimes dead parts of the leaf margins were observed. The rate of photosynthesis was significantly lowered and the pigments content was highly reduced as a response to clethodim spraying. Moreover, other gas-exchange properties were altered. Furthermore, accumulation of high amounts of carbohydrates, proteins and proline were detected. SA spraying three days prior clethodim application caused partially or totally disappearance of clethodim injuries and kept the leaves similar to those of control. Improved photosynthesis and enhanced pigments content were observed in leaves treated with SA. Other analyzed parameters showed values similar to those of the corresponding control. From the experimental work, an evidenced role of SA working against clethodim effects was suggested and discussed in this paper.

Salicylic acid induced alleviation of oxidative stress caused by clethodim in maize (Zea mays L.) leaves

Salicylic acid is used for regulation of oxidative stress in plants subjected to unfavorable environmental conditions. Application of herbicides for the purpose of weed killing can affect not only the weeds but also the main crop as well. Many herbicides have the ability to cause oxidative stress and further degradation of cell components. In this work, SA was used to alleviate the oxidative stress caused in response to clethodim herbicide in maize leaves. The results demonstrated that, spraying of clethodim caused yellowing of leaves and sometimes browning or drying of leaf tips with high clethodim doses. Contrary, leaves showed no injuries when treated with 1mM SA 3days prior clethodim application. Elevated amounts of H2O2 and MDA were detected in clethodim treated leaves compared with control indicating ROS formation and lipid peroxidation. Excessive ROS formation led to oxidative stress which followed by degradation of membranous structures. In SA treated leaves, the contents of H2O2 and MDA were more or less similar to the corresponding controls. A change in the antioxidant enzymes activities due to clethodim and SA treatment was noticed. For example, the activities of POD and APX were induced while SOD and CAT were more or less reduced in response to clethodim. SA treatment prior clethodim application could induce POD but inhibit CAT. Moreover, SOD and APX activities were adjusted to be similar to those of the control. Another mechanism of SA regulation of the oxidative stress occurred through the formation of antioxidants in the form of phenolic compounds. For that, spraying SA with or without clethodim could accumulate phenolic compounds greatly. The DPPH free radical scavenging assay for leaf extracts had confirmed a change in antioxidant status. Furthermore, SA could enhance accumulation of total proteins and free amino acids in clethodim and SA treated leaves compared with the control. This work was to provide evidence for the ability of SA to regulate clethodim herbicide detoxification through regulation of the antioxidant status of maize leaf cells.

Herbicides and Mowing to Control Barb Goatgrass (Aegilops triuncialis) and Restore Native Plants in Serpentine Grasslands

AbstractSerpentine grasslands are relatively free of the invasive species that typify other California grasslands, but recently are threatened by the spread of barb goatgrass, a Eurasian annual that is unique in its tolerance of serpentine soils. We evaluated two graminicides (clethodim and fluazifop), one broad-spectrum herbicide (glyphosate), mowing, and hand pulling for their effectiveness in controlling barb goatgrass and for restoring native species cover and diversity. We also evaluated application timing for the graminicides: before goatgrass flowering (early season), at flower initiation (midseason), and at early seed development (late season). Glyphosate was applied at early seed development. The 10 treatment combinations were applied to 10 blocks of 4-m2 (43-ft2) experimental plots in an inner Coast Range serpentine grassland with high cover of barb goatgrass but few other nonnative species. After 2 yr of treatment, all treatments except glyphosate reduced goatgrass frequency. Hand pulling, fluazifop, and mowing were most effective at controlling goatgrass, reducing frequency by 60, 51, and 48%, respectively (compared to a 30% increase on control plots). Midseason applications of clethodim and fluazifop were more effective than those applied early or late. Hand pulling, fluazifop, and clethodim increased native forb frequency by 31, 46, and 74%, respectively, with the benefit of the graminicides decreasing with later applications. Native grasses were at least partially resistant to the graminicides. Cover of one sided blue grass (Poa secunda), the most widespread native grass, might have been reduced slightly by early-season applications but was increased by late-season applications. Cover of soft brome (Bromus hordeaceus), the only other widespread nonnative species in the study, was reduced by early-season applications of the graminicides. Clethodim and fluazifop show great potential to selectively remove barb goatgrass and other nonnative annual grasses in grasslands that are otherwise dominated by native grasses and forbs. Mowing is a less selective, but viable alternative.

Natural Grassland Response to Herbicides and Application Timing for Selective Control of Tall Fescue, an Invasive Cool-Season Grass

AbstractNatural grasslands are one of the most threatened ecosystems in North America. Conservation efforts are often hampered by exotic plant invasions in existing remnant natural grasslands. Tall fescue [Schedonorus phoenix(Scop.) Holub.] is an introduced cool-season (C3) forage/turf grass which readily invades natural grasslands in Kentucky and neighboring states. Our study objectives were to (1) compare the efficacy and application timing effect of clethodim to that of imazapic to selectively remove tall fescue from natural grasslands and (2) evaluate the response of the nontarget grassland plant community (i.e., native grass and forb canopy cover) following herbicide treatments. Clethodim and imazapic treatments consisted of early (April 4, 2001) and late (April 20, 2001) applications, and these were applied at 0.23 and 0.21 kg ai ha−1, respectively. Both herbicides reduced tall fescue cover (P ≤ 0.05); herbicide application timing had no effect on herbicide efficacy to control tall fescue. Native grass cover was higher (P ≤ 0.05) in all herbicide-treated plots compared to the untreated controls, except for the late clethodim-treated plots. All herbicide treatments increased forb abundance compared to controls. Spring applications of clethodim were equally effective to those of imazapic at controlling tall fescue in natural grasslands. Imazapic released native grasses better than clethodim, whereas clethodim was better at increasing forb abundance. Furthermore, early clethodim treatments had fewer nontarget effects on native C4grasses compared to late clethodim treatments. Overall, clethodim shows promise as a beneficial management tool for tall fescue control in C4-dominated natural grasslands.