M.M. Trezzi

Multiple resistance of acetolactate synthase and protoporphyrinogen oxidase inhibitors in Euphorbia heterophylla biotypes.

Abstract Resistance to acetolactate synthase (ALS)-inhibiting herbicides in Brazil has been documented for six species. The probability to select biotypes of Euphorbia heterophylla (EPPHL) with multiple resistance increases in the same order of magnitude as the use of other herbicides belonging to only one mechanism of action. The objectives of this work were to evaluate the distribution of resistant populations (R) in the states of the Paraná and Santa Catarina; to determine the existence of populations of EPHHL with multiple resistance to ALS and PROTOX inhibitors, and to confirm the occurrence of cross resistance to compounds of these mechanisms of action. Seeds of EPHHL of areas with suspected resistance had been sampled in 97 places during 2003. In the greenhouse experiment samples of each population were sprayed with imazethapyr or fomesafen, at only one rate. To identify the resistant ones they were sprayed with different levels of the herbicides imazethapyr and fomesafen. Later they were sprayed with diverse herbicides of the same mechanisms of action to confirm the multiple/cross resistance. There is widespread distribution in the region of populations with resistance to ALS inhibitors. Some biotypes demonstrated resistance to herbicides from the two mechanisms of action. The resistance factor (FR), or the relation of resistance between R and susceptible biotypes, confirms the existence of two biotypes of EPHHL with cross resistance to several herbicides inhibitors of ALS and PROTOX.Resistance to acetolactate synthase (ALS)-inhibiting herbicides in Brazil has been documented for six species. The probability to select biotypes of Euphorbia heterophylla (EPPHL) with multiple resistance increases in the same order of magnitude as the use of other herbicides belonging to only one mechanism of action. The objectives of this work were to evaluate the distribution of resistant populations (R) in the states of the Parana and Santa Catarina; to determine the existence of populations of EPHHL with multiple resistance to ALS and PROTOX inhibitors, and to confirm the occurrence of cross resistance to compounds of these mechanisms of action. Seeds of EPHHL of areas with suspected resistance had been sampled in 97 places during 2003. In the greenhouse experiment samples of each population were sprayed with imazethapyr or fomesafen, at only one rate. To identify the resistant ones they were sprayed with different levels of the herbicides imazethapyr and fomesafen. Later they were sprayed with diverse herbicides of the same mechanisms of action to confirm the multiple/cross resistance. There is widespread distribution in the region of populations with resistance to ALS inhibitors. Some biotypes demonstrated resistance to herbicides from the two mechanisms of action. The resistance factor (FR), or the relation of resistance between R and susceptible biotypes, confirms the existence of two biotypes of EPHHL with cross resistance to several herbicides inhibitors of ALS and PROTOX.

Estresse oxidativo em girassol (Helianthus annuus) indica sinergismo para a mistura dos herbicidas metribuzin e clomazone

Biochemical and physical-chemical determinations can help verify the type of herbicide interaction. Three experiments were conducted with two oxidative stress generating herbicides to demonstrate possible synergism in their association. Sunflower plants were grown in nutrient solution up to the stage of two pairs of leaves, followed by herbicide application. Treatments consisted of metribuzin at 0 and 0.28xa0µmolxa0L-1 and clomazone at 0 and 80xa0µmolxa0L-1, in four replicates, alone and in combination. In the material collected, three days after application, malondialdehyde content was determined by the TBARS method. In another experiment, the herbicides were tested over fortyxa0 4 mm sunflower leaf discs in 5xa0mL of MESNaOH pH 6.5 buffer. Treatments consisted of metribuzin at 0 and 12xa0µmolxa0L-1 and clomazone at 0 and 237xa0µmolxa0L-1, in four replicates, alone and in combination. The treated leaf discs were dark-incubated for 24 h at 24xa0°C and light-incubated for 36 h at the same temperature. Electrolyte leakage of the solution was then measured. Compared to application of metribuzin and clomazone alone the two herbicide combination increased the MDA equivalent in 217% and 166%, and electrolyte leakage in 37 and 41%, respectively. These results demonstrate the existence of synergism in the metribuzin/clomazone combination at the studied rates, at a biochemical and physical-chemical level.

Sinergismo potencial entre herbicidas inibidores do fotossistema II e da síntese de carotenóides

Herbicides that inhibit the electron transport on the photosystem II (PSII) generate oxidative stress. This stress normally is attenuated by carotenoids, which dissipate the electron energy as heat. Hence, we hypothesize that mixtures between PSII inhibitors and carotenoid inhibitors can result in synergism. The objective of this work was to verify the existence of synergism in mixtures of herbicides from both mechanisms of action. Two experiments were conducted in 1998-99 growing season, one with corn, in the USA, and another with soybean in Brazil. At the corn trial, the treatments consisted of isoxaflutole at 52.5g ha-1, atrazine at 840g ha-1, the mixture of both herbicides, and a weedy control. At the soybean trial, the treatments consisted of metribuzin at 280g ha-1, clomazone at 560g ha-1, the mixture of both herbicides, with additional isolated treatments of metribuzin at 560g ha-1, clomazone at 1,120g ha-1, a weed-free and a weedy control. At the corn crop, assessment included the densities of Abutilon theophrasti (ABUTH), Ipomoea hederacea (IPOHE) and Amaranthus retroflexus (AMARE) at 52 days after the treatments (DAT); and the corn grain yield. At the soybean crop, assessment included Bidens pilosa (BIDPI) density, at 30 and 55 DAT; BIDPI cover, control, dry matter and leaf area, at 55 DAT; and soybean grain yield. Apparent herbicide antagonism occurred at the ABUTH, AMARE and IPOHE control, however, herbicide synergism was observed in the corn grain yield. BIDPI results demonstrated synergism for weed cover and control. Despite the complexity to demonstrate herbicide synergism in the field, the results indicate, at least to one species, the occurrence of synergism in the mixture between PSII inhibitors and carotenoid inhibitors.

Sorptive Behavior of Sorgoleone in Ultisol in Two Solvent Systems and Determination of Its Lipophilicity

Sorgoleone (SGL) exuded by sorghum roots inhibits the development of some weeds. Due to its high hydrophobicity, it is expected that SGL presents low soil mobility and limited allelopathic activity in the field. This work aims to evaluate the sorptivity of sorgoleone in octanol-water and in soil under two solvent systems. The two solvent systems were methanol:water (60:40) (MeOH:H2O) and pure methanol (MeOH). These two solvent systems promote different conditions for SGL solubility. Treatments were arranged in a 2 × 6 factorial (solvent systems × equilibrium concentrations in the solution (EC)). For each solvent, the sorption was achieved by shaking 500 mg of soil with 10 ml of 0, 5, 10, 15, 25, 40, and 60 mg L−1 of SGL solution, during 24 h. After centrifugation, the supernatant was filtered and the SGL concentration was determined by high performance liquid chromatography (HPLC). Data of sorbed amount of SGL were submitted to variance analysis, using a hierarchic factorial model. The data of sorbed amount (x/m) and equilibrium concentration (C) were fitted to the linear (x/m = a + K d C) and to the Freundlich (x/m = K f C 1/n ) models. The isotherm obtained for the MeOH:H2O system presented linear shape, whereas for the MeOH system a two subsequent linear isotherm was fitted. Sorgoleone is a highly hydrophobic compound, presenting a log K ow of 6.1. The sorption of sorgoleone to the soil was very high. The organic environment stimulated the sorgoleone sorption to the soil.

Resistência ao glyphosate em biótipos de buva (Conyza spp.) das regiões oeste e sudoeste do Paraná

A resistencia ao glyphosate em biotipos de Conyza spp. em areas de lavoura das regioes oeste e sudoeste do Parana causa grandes dificuldades ao manejo e, consequentemente, problemas economicos e ambientais. Este experimento objetivou determinar a existencia de resistencia ao herbicida glyphosate em biotipos de buva (Conyza spp.) suspeitos, coletados em lavouras das regioes oeste e sudoeste do Parana, comparando-os com biotipos suscetiveis. O delineamento experimental utilizado foi inteiramente casualizado, em esquema fatorial 12 x 8 x 3. Os fatores consistiram de 12 biotipos de buva, doses de glyphosate (0, 100, 180, 324, 583, 1.050, 1.888 e 3.345 g ha-1) e epocas de avaliacao para a variavel controle (7, 14 e 21 dias apos a aplicacao). Para as variaveis materia verde e materia seca, o esquema fatorial utilizado foi o 12 x 8. As variaveis avaliadas foram controle visual, materia verde, materia seca, C50, GR50 e fator de resistencia. A dose de 3.345 g glyphosate ha-1 foi a que apresentou maior nivel de controle dos biotipos, porem o controle dos biotipos suspeitos nao foi efetivo, necessitando de doses mais altas. Todos os biotipos de buva suspeitos de resistencia ao glyphosate tiveram essa caracteristica confirmada. Entretanto, constatou-se grande amplitude de fatores de resistencia, o que caracteriza a variabilidade entre os biotipos resistentes. Essas informacoes poderao ser utilizadas no planejamento de estrategias de manejo das populacoes resistentes e na prevencao da ocorrencia de novas areas com buva resistente ao glyphosate.

Manejo químico de plantas daninhas na cultura do milho em função de características morfofisiológicas e redução de espaçamento da cultura

This work was carried out to evaluate the effect of integrating morphophysiological characteristics of hybrids, row spacing reduction and chemical weed management in corn. The experiment was carried out under field conditions, in a randomized complete block design, in a 2xa0xxa02xa0xxa05 factorial scheme, with four replications, with the first factor consisting of corn hybrids (Sprint, too early-maturing and more erect leaves and Penta, early-maturing and more plane leaves),and the second consisting of row spacing (0.45 and 0.90xa0m) and the third, of the weed control treatments: 1.atrazinexa0+xa0simazine (1.500xa0+xa01.500xa0g.a.i.xa0ha-1 ) at early post-emergence; 2.atrazinexa0+xa0simazine (1.500xa0+xa01.500xa0gxa0a.i.xa0ha-1), in early post-emergence, complemented by nicosulfuron+atrazine (20xa0+xa0750xa0gxa0a.i.xa0ha-1 ), at late post-emergence; 3.atrazine+simazine (750xa0+xa0750xa0gxa0a.i.xa0ha-1 ), at early post-emergence; 4.control with weeding; 5.xa0only nicosulfuron+ atrazine (20xa0+xa0750xa0gxa0a.i.xa0ha-1 ), in late post-emergence. The 45xa0cm spacing favored weeds in the row while in the 90xa0cm spacing, the greatest weed infestations occurred in the interrows. Complementary applications of atrazinexa0+xa0nicosulfuron were needed to control weeds in the Spring hybrid and conventional row systems, but not to control Penta at the row width used. For the Penta hybrid, reduced spacing decreased corn grain yield, while for the Sprint hybrid, no corn grain yield reduction was observed.

Eficácia de controle de plantas daninhas e toxicidade ao milho da mistura de foramsulfuron e Iodosulfuron isoladamente ou em associação com atrazine e/ou clorpirifós

Two trials evaluated corn toxicity and weed control efficacy of the herbicides atrazine, foramsulfuron, and iodosulfuron and the insecticide chlorpyriphos applied at postemergence alone or in mixture. A randomized complete block design was used with four replications. In the first trial, the treatments (weed free throughout cultivation) were: atrazine (3000g ha-1 of a.i.); atrazine + clorpyriphos (3000 + 225g ha-1 of a.i.), atrazine + foramsulfuron + iodosulfuron + chlorpyriphos (2,250 + 15 + 1+ 225; 1,500 + 22.5 + 1.5 + 225 and 750 + 30 + 2 + 225 g ha-1 of a.i.); foramsulfuron+ iodosulfuron (45 + 3 g ha-1 of a.i.); foramsulfuron + iodosulfuron + chlorpyriphos (45 + 3 + 225 g ha1 of a.i.), and a check without herbicides. In the second trial, the same treatments were used, except for atrazine + foramsulfuron + iodosulfuron + chlorpyriphos (750 + 30 + 2 + 225 g ha-1 of a.i.), besides the same treatments above without weed cultivation. AG 3010 cultivar, a short-cycle double hybrid, tolerant to ALS herbicides, was used. During the 2002/2003 agricultural season, corn toxicity and grain yield were evaluated, while during 2003/2004 ,weed control efficacy was also evaluated. Atrazine alone or mixed with chlorpyriphos did not cause any toxicity to the corn plants. Chlorpiryphos + foramsulfuron and iodosulfuron association can increase corn plant injury. The inclusion of atrazine concomitant to foramsulfuron and iodosulfuron reduction allowed partial reduction of corn plant injury, maintaining BRAPL control and enhancing the level of EPHHL control.

Prospección de las combinaciones de herbicidas para prevenir malezas tolerantes y resistentes al glifosato

The intense use of glyphosate in Argentina has increased the spread of weeds with tolerance to this herbicide, like Ipomoeaxa0nil. Cases of weed resistance to ALS inhibitors were documented in Argentina with Amaranthus quitensis. Likewise, in Brazil, it has increased weed resistance to glyphosate in weeds such as Lolium multiflorum and Euphorbiaxa0heterophylla. The objective of this research was to assess antagonism or synergism to control of the mentioned weeds for all possible combinations between two of the following herbicides: glyphosate, imazethapyr, clomazone, and lactofen. Biotypes susceptible to all herbicides were used in the research. Seedlings of A.xa0hybridus with two cm and of the others with seven cm, were treated with the herbicides glyphosate, imazethapyr, clomazone and lactofen at 108, 10, 160 y 30xa0g ha-1xa0a.i. respectively, applied alone. Six additional treatments were included in all possible combinations between two of the herbicides and doses as described above. An untreated control was also used. A non-ionic adjuvant at a ratio of 0.2% was added to all treatments, except for the treatment of glyphosate alone and the untreated. The effect of the herbicide mixtures depended on the species tested and also on the herbicides used. Synergism was obtained only in the mixture glyphosate + imazethapyr. Clomazone resulted predominantly in antagonism, and lactofen had a neutral effect in most of the evaluated herbicide mixtures. Herbicide combinations are considered potentially useful in controlling weeds resistant or tolerant to glyphosate.

Antagonismo das associações de clodinafop-propargyl com metsulfuron-methyl e 2,4-D no controle de azevém (Lolium multiflorum)

The efficacy of ACCase inhibitors is usually reduced when tank-mixed with broad leaf herbicides. A greenhouse and a field experiments were carried out to determine the existence of antagonistic effects of clodinafop-propargyl associated with metsulfuron methyl or 2,4-D to control Italian ryegrass (Lolium multiflorum). In the greenhouse experiment, 21 treatments were tested, composed by clodynafop(0, 3, 6, 12, 24, 48 and 96 g ha-1) alone or tank-mixed with metsulfuron (2 and 4 g ha-1) or 2,4-D (470 g ha-1). In the field experiment, twelve treatments were set up in a factorial 6 x 2, composed by clodinafop (0, 3, 6, 12, 24, 48 and 96 g ha-1) alone or tank-mixed with metsulfuron (2 g ha-1). In the greenhouse experiment, the control (visual evaluation), I50 from the mixtures with metsulfuron (2 and 4 g ha-1) or 2,4-D (470 g ha-1) were 33, 84 and 151% higher than clodinafop applied alone. The I50 from the rye live matter from the mixtures cited above were, respectively, 119, 244 and 72% higher than clodinafop applied alone. In the field experiment, rye live matter reduction was observed with increase of the levels of clodinafop applied alone, but rye live matter did not decrease, changing the levels of clodinafop tank-mixed with metsulfuron. The results reveal the antagonistic effect of tank-mixtures of clodinafop and metsulfuron or 2,4-D. We did make some considerations on the advantages of applying herbicides in more than one control operation, in comparison to graminicide and latifolicide mixtures.

Eletrolite leakage as a technique to diagnose euphorbia heterophylla biotypes resistant to ppo-inhibitors herbicides

A acao de herbicidas que afetam a integridade das membranas celulares e causam extravasamento, como os inibidores da Protox, pode ser detectada atraves da medicao da condutividade eletrica (CE) de uma solucao em que tecidos da planta-alvo sao incubados na presenca de herbicida. Os objetivos deste trabalho foram confirmar a resistencia a inibidores da Protox em um novo biotipo de Euphorbia heterophylla (EPHHL) do Brasil, e comparar o extravasamento eletrolitico em biotipos R e S a inibidores da Protox, utilizando dois metodos diferentes de incubacao em solucao contendo herbicidas. Um experimento foi conduzido em casa de vegetacao, e tres em laboratorio, em delineamento inteiramente casualizado. No experimento em casa de vegetacao, quatro biotipos de EPHHL foram pulverizados com sete niveis de fomesafen, para confirmar a resistencia em biotipos suspeitos. No segundo e terceiro experimentos, discos foliares de biotipos de EPHHL R e S e, no quarto experimento, a folha inteira, foram incubados em solucao contendo inibidores da Protox, para depois determinar a CE da solucao. O estudo confirmou a resistencia aos inibidores da Protox em dois novos biotipos de EPHHL suspeitos. Em experimentos com incubacao de discos foliares nao houve diferencas significativas entre os biotipos R e S. Mas, na incubacao de folhas inteiras de EPHHL com fomesafen, o biotipo S apresentou maior CE, em comparacao ao biotipo R. Os resultados deste trabalho sao uma evidencia indireta de que a resistencia aos inibidores da enzima Protox esta relacionada a menor absorcao de herbicidas pela parte aerea e tambem a algum mecanismo para fazer frente ao estresse oxidativo.