Hormetic Effect of Glyphosate on the Morphology, Physiology and Metabolism of Coffee Plants.

Glyphosate is a nonselective herbicide of systemic action that inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, thus compromising amino acid production and consequently the growth and development of susceptible plants. The objective of this study was to evaluate the hormetic effect of glyphosate on the morphology, physiology, and biochemistry of coffee plants. Coffee seedlings (Coffea arabica cv Catuaí Vermelho IAC-144) were transplanted into pots filled with a mixture of soil and substrate and subjected to ten doses of glyphosate: 0, 11.25, 22.5, 45, 90, 180, 360, 720, 1440, and 2880 g acid equivalent (ae) ha-1. Evaluations were performed using the morphological, physiological, and biochemical variables. Data analysis for the confirmation of hormesis occurred with the application of mathematical models. The hormetic effect of glyphosate on coffee plant morphology was determined by the variables plant height, number of leaves, leaf area, and leaf, stem, and total dry mass. Doses from 14.5 to 30 g ae ha-1 caused the highest stimulation. In the physiological analyses, the highest stimulation was observed upon CO2 assimilation, transpiration, stomatal conductance, carboxylation efficiency, intrinsic water use efficiency, electron transport rate, and photochemical efficiency of photosystem II at doses ranging from 4.4 to 55 g ae ha-1. The biochemical analyses revealed significant increases in the concentrations of quinic acid, salicylic acid, caffeic acid, and coumaric acid, with maximum stimulation at doses between 3 and 140 g ae ha-1. Thus, the application of low doses of glyphosate has positive effects on the morphology, physiology, and biochemistry of coffee plants.

Low doses of glyphosate do not damage the secondary metabolism of common bean.

Glyphosate application, even in low doses, changes the metabolism of crops. This research aimed to evaluate the effects of glyphosate low doses and sowing season on metabolic changes of early-cycle common beans. Two experiments were conducted in the field, one in the winter season and one in the wet season. The experimental design was a randomized complete block design consisting of the application of glyphosate low doses [0.0, 1.8, 7.2, 12.0, 36.0, 54.0, and 108.0 g acid equivalent (a.e.) ha-1] in the phenological stage V4 with four replications. In the winter season, glyphosate and shikimic acid were increased five days after the application of treatments. In contrast, the same compounds increased only at doses of 36 g a.e. ha-1 and above in the wet season. The dose of 7.2 g a.e. ha-1 increased phenylalanine ammonia-lyase and benzoic acid in the winter season. The doses of 54 and 108 g a.e. ha-1 increased benzoic acid, caffeic acid, and salicylic acid. Our study indicated that glyphosate low doses increase the concentration of shikimic, benzoic, salicylic and caffeic acid, PAL and tyrosine. There was no reduction in aromatic amino acids and in secondary compounds from the shikimic acid pathway.

Dynamics and weed control effectiveness of dicamba herbicide when applied directly on the soil and corn straw in Brazil.

Dicamba is a post-emergence herbicide commonly used to control broadleaves in cereal crops. However, a portion of the herbicide might reach soil surface, and many factors could affect its dynamics and effects. The objective of this research was to evaluate the dynamics of dicamba applied to the soil, to the soil and covered with straw and over the straw, in addition, to evaluate the weed control in pre-emergence. Two field experiments at different locations were conducted with dicamba. To quantify dicamba in the soil a LC-MS/MS system was used. In both experiments, rainfall and straw played a key role in dicamba soil dynamics and weed control. Dicamba in the soil was affected by presence of straw and accumulated rainfall after the application. Higher concentrations (254-432 ng g soil-1) in the soil 0-10 cm layers and greater leaching potential were found for the application in the soil compared to over the straw. The maximum concentration of dicamba (101.6-226 ng g soil-1) was found after 10 mm of rainfall for dicamba application over the straw. Around 60-70% of weeds were controlled with concentrations greater than 20 ng/g soil-1, in the presence or absence of straw.

Dynamics of 2,4-D and Dicamba Applied to Corn Straw and Their Residual Action in Weeds.

2,4-D and dicamba are used in the postemergence management of eudicotyledonous weeds in different crops, most of which are grown under no-tillage systems. Due to the application methods for these products, their dynamics in straw and their residual action in soil have rarely been explored. Thus, the objective of this study was to evaluate the dynamics of 2,4-D and dicamba that have been applied to corn straw and to verify their relationship with residual control action in weeds. In the dynamics experiments, the herbicides were applied to 5 t ha-1 of straw, and rainfall simulations were performed with variable amounts and at different periods after application to evaluate herbicide movement in the straw. In the residual action experiments, the species Digitaria insularis, Conyza spp., Bidens pilosa, Amaranthus hybridus, Euphorbia heterophylla, and Eleusine indica were sown in trays, and 2,4-D and dicamba were applied directly to the soil, to the soil with the subsequent addition of the straw, and to the straw; all of these applications were followed by a simulation of 10 mm of rain. The physical effect of the straw and the efficacy of the herbicides in terms of pre-emergence control of the weed species were evaluated. The leaching of 2,4-D and dicamba from the corn straw increased with a higher volume of rainfall, and the longer the drought period was, the lower the final amount of herbicide that leached. The presence of the corn straw on the soil exerted a physical control effect on Conyza spp.; significantly reduced the infestation of D. insularis, B. pilosa, A. hybridus, and E. indica; and broadened the control spectrum of 2,4-D and dicamba, assisting in its residual action and ensuring high levels of control of the evaluated weeds. In the absence of the straw, 2,4-D effectively controlled the pre-emergence of D. insularis, Conyza spp., and A. hybridus, and dicamba effectively controlled D. insularis, Conyza spp., B. pilosa, A. hybridus, E. heterophylla, and E. indica.

Glyphosate hormesis attenuates water deficit stress in safflower (Carthamus tinctorius L.) by modulating physiological and biochemical mediators.

Changes in photosynthetic machinery can induce physiological and biochemical damage in plants. Low doses of glyphosate have been shown to exert a positive effect in mitigating the deleterious effects of water deficit in plants. Here, the physiological and biochemical mechanisms of safflower plants (Carthamus tinctorius L.) were studied under conditions of water deficit mediated by the attenuating effect of low-dose glyphosate. The plants were divided into two groups of water regimes in soil, without water deficit (-10 kPa) and with water deficit (-70 kPa), and were exposed to different concentrations of glyphosate (0, 1.8, 3.6, 7.2, 18, 36, 72, 180, 360, and 720 g a.e. ha-1). Evident protective responses at the physiological and biochemical levels were obtained after applying low doses of glyphosate to plants under water deficit, with a limiting dose for the occurrence of hormesis (LDS) = 72 g a.e. ha-1. The water deficit in plants resulted in hydrogen peroxide (H2O2) accumulation and consequently lipid peroxidation (LPO) associated with the accumulation of shikimic acid and glyphosate in plants, which triggered an increase in the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) that act by dismuting the levels of reactive oxygen species (ROS), maintaining, and/or increasing the maximum quantum efficiency of photosystem II (Fv/Fm), effective quantum yield of photosystem II (ΦPSII), electron transport rate (ETR), photochemical extinction coefficient (qP), and non-photochemical extinction coefficient (NPQ). APX appears to be the main enzyme involved in eliminating H2O2. Low doses of glyphosate act as water deficit ameliorators, allowing the plant to maintain/increase metabolism at physiological and biochemical levels by activating antioxidant enzymes in the dismutation of ROS in safflower plants.

Detection of herbicides in water bodies of the Samambaia River sub-basin in the Federal District and eastern Goiás.

The objective of this study was to identify and quantify herbicide residues in water samples of rain, cisterns, streams, ponds, springs, semi-artesian wells, dams and a river in the Rio Samambaia sub-basin in the Federal District and eastern Goiás. A total of 287 samples were collected from 20 farms in the sub-basin in the rainy (February, summer) and dry (August, winter) seasons in 2016. Aminomethylphosphonic acid (AMPA, a glyphosate metabolite), clethodim, chlorimuron-ethyl, diuron, fluazifop acid (a fluazifop-p-butyl metabolite and the active ingredient), haloxyfop acid (a haloxyfop-methyl metabolite and the active ingredient), imazamox, mesotrione, metsulfuron, nicosulfuron and pendimethalin were not identified in any water sample. In the rainy season, approximately 99% of the samples contained residues at least one of the evaluated herbicides; in the dry season (, 100% of the samples contained residues of at least one of the evaluated herbicides. When considering only detection frequency, metribuzin, atrazine, clomazone and haloxyfop-methyl were the main herbicides found in the water of the Samambaia River sub-basin. In turn, based on levels higher than the limit of quantification, the main compounds detected were atrazine, clomazone, haloxyfop-methyl and glyphosate. In both seasons, the highest relative concentrations of herbicides for the rainy and dry seasons were found in spring water, 25% and 56%, respectively, and dam water, 23% and 16%, respectively.

Performance of herbicides in sugarcane straw / Dinâmica de herbicidas em palha de cana-de-açúcar

The process of mechanical harvesting of sugarcane generates a large deposition of straw on the soil surface, providing a coverage that several studies have found important for reducing the weed population. Although such coverage reduces weed infestations, additional management, including chemical control, is still needed. Thus, this study aimed to evaluate the leaching of atrazine, pendimethalin, metribuzin, clomazone, diuron and hexazinone in sugarcane straw. The experiment was conducted at the School of Agronomic Engineering at UNESP (Sao Paulo State University) - Botucatu/SP. The sugarcane straw was collected in the field, cut and placed in quantities of 10t ha-1 in the capsules used as experimental units. The experimental design was completely randomized, using six herbicide treatments and four replications. Within 24 hours after the herbicides were applied in capsules with straw, five different rainfalls (5, 10, 20, 50 and 100mm) were simulated. The leached water was collected for chromatographic analysis. The herbicide percentages that crossed the straw layer were statistically correlated with the rainfall amount by the Mitscherlich model that compares the facility of herbicide removal from sugarcane straw. In summary, pendimethalin did not present quantified transposition of the product by sugarcane straw even with a rain simulation of 100 mm. Furthermore, two different profiles of facility to transpose the herbicides in straw were found: one for metribuzin and hexazinone that crossed quickly through the straw layer and another for atrazine, diuron and clomazone that required more rainfall to be leached from coverage to the soil according to the maximum removable amount of each herbicide.

O processo de colheita mecanizada de cana-de-açúcar gera uma grande quantidade de palhada depositada na superfície do solo e vários trabalhos destacam a importância da manutenção dessas coberturas em sistemas de cana crua, com destaque na redução da população de plantas daninhas. Mas, apesar de a cobertura vegetal reduzir a infestação das plantas daninhas, medidas complementares, como o controle químico, ainda são necessárias. Dessa forma, o objetivo deste estudo foi avaliar a transposição dos herbicidas atrazine, pendimethalin, metribuzin, clomazone, diuron e hexazinone em palha de cana-de-açúcar. O experimento foi desenvolvido na Faculdade de Ciências Agronômicas da UNESP - Botucatu/SP. A palha da cana-de-açúcar foi coletada em campo, cortada e colocada em quantidades de 10t ha-1 em recipientes plásticos utilizados como unidades experimentais. O delineamento experimental foi inteiramente casualisado, e foram testados seis tratamentos (atrazine, pendimethalin, metribuzin, clomazone, diuron e hexazinone) e quatro repetições. Nas cápsulas com palha e pulverizadas, foi realizado, no período de 24 horas após a aplicação, a simulação de diferentes lâminas de chuva (5, 10, 20, 50 e 100mm) e coletada a água lixiviada para posterior quantificação cromatográfica. Como análise estatística, os herbicidas foram correlacionados com as lâminas de chuva e foi usado o modelo de Mitscherlich para ajuste dos dados, que permitiu comparar a facilidade de remoção dos herbicidas pela palha. Em síntese, para o pendimethalin, não se observou transposição quantificada do produto pela palha de cana-de-açúcar, mesmo com uma lâmina de 100mm de chuva. Foram encontrados dois perfis diferentes de facilidade de transposição dos herbicidas em palha: um para o metribuzin e hexazinone, que passaram rapidamente pela camada de palha, e outro para atrazine, clomazone e diuron, que precisaram de uma quantidade superior de chuva para serem lixiviados da cobertura vegetal, em função da quantidade máxima removível dos herbicidas.

Detecção da tolerância de diferentes espécies de capim-colchão a herbicidas inibidores do fotossistema II utilizando a técnica da fluorescência / Detection of crabgrass species tolerance to photosystem II inhibitor herbicides using fluorescence technique

Este estudo teve como objetivo investigar a tolerância ou susceptibilidade das espécies de capim-colchão (Digitaria ciliaris, D. horizontalis e D. nuda) a herbicidas inibidores do fotossistema II (FSII), por meio da técnica da fluorescência, utilizando a taxa de transferência de elétrons do FSII como indicador. Para isso, foi conduzido um experimento em esquema fatorial 3x6, com três espécies de capim-colchão e seis tratamentos (ametryn, hexazinone, diuron+hexazinone, amicarbazone, diuron, tebuthiuron e testemunha) aplicados em pós-emergência. Foi monitorada a taxa de transporte de elétrons (ETR) do FSII em intervalos de tempo crescente e aferida a massa seca das plantas aos 21 dias após a aplicação. A partir dos dados da ETR, calculou-se um valor numérico representativo da taxa de inativação da ETR. Os resultados demonstraram que todas as espécies de capim-colchão estudadas são susceptíveis aos herbicidas ametryn e hexazinone (valores da taxa de inativação da ETR superiores a 10.000). Os herbicidas diuron e tebuthiuron apresentaram menores taxas de inativação da ETR para a D. nuda (3.585 e 3.497, respectivamente) e maiores para as espécies D. ciliaris e D. horizontalis (acima de 10.000), enquanto que o herbicida amicarbazone apresentou valor intermediário para D. nuda (7.967). O monitoramento da ETR foi eficiente para verificar a atuação dos herbicidas nas diferentes espécies estudadas.

This study aimed to investigate the tolerance or susceptibility of crabgrass species (Digitaria ciliaris, D. horizontalis and D. nuda) to herbicides that target photosystem II (PSII), by fluorescence technique using the electron transport rate (ETR) through PSII as an indicator. An experiment was conducted under a factorial arrange (3x6), with three species of crabgrass and six treatments (ametryn, hexazinone, diuron+hexazinone, amicarbazone, diuron, tebuthiuron and control) applied in post-emergence. The ETR through PSII was monitored over time and the plants dry weight measured at 21 days after application. A numerical value of the ETR inactivation was calculated from the data collected. The results showed that the three crabgrass species studied are susceptible to ametryn and hexazinone (ETR inactivation value higher than 10,000). Moreover, diuron and tebuthiuron provided lower ETR inactivation for D. nuda (3,585 and 3,497, respectively) and higher rates for D. horizontalis and D. ciliaris (more than 10,000), whereas amicarbazone showed intermediate inactivation rate for D. nuda (7,967). Monitoring the ETR showed to be an efficient form to verify the herbicides performance in the different species studied here.

Aplicação em subdose do haloxyfop-methyl na aveia-preta / Low doses of haloxyfop-methyl in black oat

Uma das limitações para sustentabilidade do sistema de cultivo em plantio direto é a rápida decomposição da matéria seca. Um dos mecanismos conhecidos para minimizar este processo e potencializar a permanência da palhada no solo é alterar as vias metabólicas dos polímeros de lignina com aplicação de subdoses de herbicida, interferindo diretamente na resistência à degradação dos restos vegetais pelos microrganismos. Com este objetivo, o herbicida Verdict*R (haloxyfop-methyl) foi aplicado em subdoses nas plantas de aveia-preta e o efeito correlacionado com a altura das plantas, produtividade da matéria seca e metabolismo de lignina. Ensaios preliminares em casa de vegetação foram realizados para determinar as faixas de subdoses a serem aplicadas no experimento definitivo em campo. Os resultados obtidos demonstraram aumento de 24% na produtividade de matéria seca dos experimentos conduzidos em casa de vegetação com a aplicação de 3,125g do ingrediente ativo de haloxyfop-methyl por hectare (i.a. ha-1) nesta subdose, não foram observadas alterações na altura e no metabolismo de lignina nas plantas de aveia-preta. No campo, a concentração de 2,5g i. a. ha-1 do haloxyfop-methyl já foi suficiente para reduzir em 9% a taxa de lignificação sem interferir na altura e produtividade das plantas, sendo este resultado favorável à velocidade de degradação da palhada no plantio direto.

One of the major constraints to sustainable of the tillage is the rapid decomposition of dry the matter. One of the mechanisms known to facilitate this process is the interference in pathways of polymers of lignin from tests of application of low doses of herbicide based on the relation that higher the content of the lignin greater the resistance to degradation. With this purpose, the herbicide Verdict * R (haloxyfop-methyl) was used to verify the effect of low doses at the height of the plants, productivity of dry matter and in the metabolism of the lignin in plants of black oat. Preliminary tests in the greenhouse were realized for adjustments ​​to the best low doses to be applied in the definitive experiment in the production area. The results obtained were 24% of increase in productivity in the experiments conducted in greenhouse, from the application of 3.125g of the active ingredient of the haloxyfop-methyl per hectare, in this subdose no changes was observed in growth and content of lignin in plants of black oat. In the field, the concentration of 2.5g i. a. ha-1 of haloxyfop-methyl decreased in 9% the lignification rate without interfering with the height and productivity of the plants, this being favorable to the degradation rate of stubble tillage on outcome.

Effects of hand weeding strip and nitrogen fertilizer on corn plants.

The objective of the present research was to evaluate effects of different strip weed control associated with nitrogen fertilizer on corn applied after planting. The experiment was set and conducted in Botucatu, São Paulo State, Brazil, and the hybrid planted was Dekalb 333-B. A completely randomized block design with four replications was used. Experimental plots were disposed as a factorial scheme 2 x 2 x 4, constituted by two types of weeding on row (with or without manual hoeing), two types of weeding on inter-row (with or without manual hoeing), and four nitrogen levels applied after planting (00, 60, 90, and 120 kg ha(-1)). Plots were composed by six rows with 5 m length. Nitrogen fertilizer was applied at 35 days after emergence (d.a.e). For weed community it was evaluated: weed density, dominancy, frequency, and relative importance. The main weed species were: Brachiaria plantiginea, Amaranthus retroflexus, Bidens pilosa, Cyperus rotunds, Brachiaria decumbens, Euphorbia heterofila, Oxalis latifolia, Acanthospermum hispidum, Commelina benghalensis. It was evaluated corn height at 40 and 100 d.a.e., first ear insertion height at 100 d.a.e., and final grain yield at harvesting. Plants and first ear insertion height were affected when nitrogen fertilizer was not applied. Treatments without weed control showed that weed interfered negatively with plants height. There were no correlation between weeds and nitrogen fertilizer for all parameters evaluated. Parcels without weed showed the highest ear weights and final grain production. Treatments that received nitrogen fertilizer, independently of studied arrangement, provided higher yields.