Evolution of ACCase-inhibitor resistance in Chloris virgata is conferred by a Trp2027Cys mutation in the herbicide target site.

BACKGROUND: Chloris virgata is a troublesome weed in tropical regions. With the evolution of glyphosate resistance in key grass species, acetyl CoA carboxylase (ACCase) inhibitors have become a commonly used tool in soybean production areas in Brazil. We assessed if suspected resistant populations exhibited cross resistance to the different classes of ACCase inhibitors and investigated the resistance mechanisms in C. virgata. RESULTS: Dose-response experiments revealed resistance to haloxyfop-methyl and pinoxaden, with 432- and 3-fold resistance, respectively, compared to susceptible populations. Due to the lack of genetic resources for C. virgata, we sequenced, assembled, and annotated the genome using short-read Illumina technology. The k-mer analysis estimated a genome size of approximately 336 Mbp, with BUSCO completeness of 97%, and over 36 000 gene models were annotated. We examined if ACCase copy number variation and increased gene expression were involved in the resistance phenotype and found no difference when compared to a susceptible population. A mutation was detected in ACCase that encodes for amino acid position 2027, resulting in a tryptophan-to-cysteine (Trp2027Cys) substitution. We found the resistant population absorbed 11.4% less herbicide and retained 21% more herbicide on the treated leaf compared to the susceptible population. We developed a genotyping assay targeting the resistance-endowing Trp2027Cys substitution for quick resistance diagnosis. CONCLUSION: A Trp2027Cys amino acid substitution in ACCase confers resistance to haloxyfop and pinoxaden in C. virgata. We provide important insights into the evolutionary history of C. virgata and a draft genome as a useful resource to further our understanding of the biology in the genus Chloris. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Withdrawal period for seeding cotton after chemical control of cotton stalks

A very limited amount of information is available in relation both to the residual effect of herbicides destinated to the destruction of cotton stalks and to the time interval required to prevent that development and yield of the following crop be affected. This work aimed to identify the residual activity of herbicides intended to eliminate cotton stalks and to estimate the safety interval (SI) of time for the next cotton sowing. Two trails were simultaneously carried out, the first one for a single application and a second one for the two sequential applications of herbicide treatments, in a 15×5 factorial design organized in randomized complete blocks with four replications. Levels of first factor were constituted by herbicide treatments and the levels of the second factor were composed five periods of time for cotton sowing after herbicide application (0, 30, 60, 90, and 120 days). Herbicides were 2,4-D, glyphosate, saflufenacil, [imazapic + imazapyr], dicamba, fluroxypyr and sulfentrazone. Results provided an indication of residual activity of herbicide treatments in soil and indicated that a single application or two sequential applications of glyphosate + dicamba + saflufenacil have a considerable potential to affect cotton and a period exceeding 100 days for a single application and exceeding 120 days for two sequential applications was necessary. Treatments with 2,4-D and 2,4-D + glyphosate provided the shortest safe interval and may be used for cotton stalk destruction with no risks for the crop sowing after the withdrawal period.

Performance of RR soybean submitted to postemergence application of glyphosate with a foliar elicitor product / Desempenho da soja RR submetida a aplicação de glifosato associado a produto elicitor foliar em pós-emergência

With the advent of glyphosate-resistant soybean, postemergence applications of the herbicide have become routine. In this way, problems related to the selectivity of glyphosate have been shown to be increasingly intense, due to the use of increased dosages and applications of the herbicide at unrecommended moments. In order to evaluate the agronomic performance of soybean plants subjected to the postemergence application of glyphosate ­ both in isolation and together with Crop+ ­ at different stages and dosage levels, a randomized block design experiment was carried out with two adjacent checks and four repetitions. The treatments consisted of: glyphosate (1296 g·ha-1); glyphosate + Crop+ (1296 + 0.25 g or L·ha-1); glyphosate + Crop+ (1296 + 0.5 g or L·ha-1); glyphosate (2592 g·ha-1); glyphosate + Crop+ (2592 + 0.25 g or L·ha-1); glyphosate + Crop+ (2592 + 0.5 g or L·ha-1); 2 × glyphosate (2 × 1296 g·ha-1); 2 × glyphosate + Crop+ (2 × 1296 + 0.25 g or L·ha-1); 2 × glyphosate + Crop+ (2 × 1296 + 0.5 g or L·ha-1) and Crop+ (0.5 g·ha-1). The phytotoxicity, soil plant analysis development (SPAD) index, height, stand, mass of 100 grains, and yield of the soybean plants were evaluated. The use of Crop+ on soybean plants led to an increase in the SPAD index; the use of Crop+ in association with glyphosate made possible the attenuation of visible symptoms of damage, preventing reductions in crop yield.(AU)

Com o advento da soja resistente ao glifosato, aplicações em pós-emergência da cultura tornaram-se corriqueiras. Dessa forma, problemas relacionados à seletividade desse herbicida mostraram-se cada vez mais intensos, devido ao aumento da dose utilizada e à aplicação em momentos não recomendados. Para avaliar o desempenho agronômico da soja submetida à aplicação de glifosato isolado em pós-emergência e em associação ao Crop+ em diferentes estádios e doses, um experimento foi realizado em delineamento de blocos ao acaso, em esquema de testemunhas duplas adjacentes, adotando-se quatro repetições. Os tratamentos foram constituídos por: glifosato (1296 g·ha-1); glifosato + Crop+ (1296 + 0,25 g ou L·ha-1); glifosato + Crop+ (1296 + 0,5 g ou L·ha-1);glifosato (2592 g·ha-1); glifosato + Crop+ (2592 + 0,25 g ou L·ha-1);glifosato + Crop+ (2592 + 0,5 g ou L·ha-1); 2 × glifosato (2 × 1296 g·ha-1); 2 × glifosato + Crop+ (2 × 1296 + 0,25 g ou L·ha-1); 2 × glifosato + Crop+ (2 × 1296 + 0,5 g ou L·ha-1) e Crop+ (0,5 g·ha-1). Foram avaliados fitointoxicação das plantas de soja, índice SPAD (soil plant analysis development), altura, estande, massa de cem grãos e produtividade. Nos resultados, a utilização de Crop+ em plantas de soja proporcionou o aumento no índice SPAD e, quando o Crop+ foi associado ao glifosato, possibilitou a atenuação dos sintomas visuais de injúrias, prevenindo reduções na produtividade da cultura.(AU)

Effect of day time climatic conditions associated with different 2,4-D formulations on spray deposition and weed control.

The aim of this study was to evaluate the effect of time of the day and their associated climatic conditions on spray deposition of two 2,4-D formulations, as well as the influence on weed control. The experiment was installed in the field in complete randomized design. Treatments were arranged in factorial design 8 × 2, with 20 repetitions. First factor corresponded to different application time (1:00, 4:00, 7:00, 10:00, 13:00, 16:00, 19:00, and 22:00) with their respective climatic conditions. The second factor consisted of two formulations of 2,4-D applied at 776 g a.e. ha-1 (2,4-D amine and 2,4-D choline salt with Colex-D™ Technology) + glyphosate (816 g a.e. ha-1). There was more spray deposition when 2,4-D choline formulation was used, and such differences were more evident for applications performed under adverse climatic conditions. More spray deposition was found in applications performed at times of day with more favorable temperature and humidity of the air conditions. Only the initial control of the evaluated species was affected by the time of application.

Effects of nozzle types and 2,4-D formulations on spray deposition.

The objective of this study was to evaluate the effects of nozzle types and 2,4-D formulations on spray deposition on different targets. Two field experiments were carried out in a completely randomized design, and treatments were arranged in a factorial scheme. Species in experiment 1 were Sumatran fleabane (Conyza sumatrensis) and Brazil pusley (Richardia brasiliensis) and in experiment 2 were soybeans (Glycine max) and Benghal dayflower (Commelina benghalensis). For both experiments, the first factor corresponded to spray nozzles with different settings (AD 110.015 - 61 and 105 L ha-1; AD 015-D - 75 and 146 L ha-1; XR 110.0202 - 200 L ha-1; and ADIA-D 110.02 - 208 L ha-1) and the second factor consisted of two formulations of 2,4-D (amine and choline). The formulation of 2,4-D choline has contained Colex-D™ Technology. Similar or higher spray deposition was observed on the leaves and artificial targets when using 2,4-D choline as compared to the 2,4-D amine formulation, and these differences in deposition were more evident for nozzles applying lower spray volumes. Deposition was more affected by nozzle type when amine formulation was used, compared to choline formulation.

Seletividade de aplicações combinadas de herbicidas em pré e pós-emergência para a soja tolerante ao glyphosate / Selectivity of combined applications of herbicides in pre and post-emergence for the glyphosate tolerant soybean

Dentro de sistemas de manejo de plantas daninhas, a aplicação de herbicidas em pré-emergência é uma opção interessante, visto que eles são uma importante ferramenta no manejo de populações resistentes. Objetivou-se com este trabalho avaliar a seletividade de herbicidas aplicados em pré-emergência na cultura da soja, combinados ou não à aplicação de glyphosate em pós-emergência, em solo de textura argilosa. O delineamento experimental foi o de blocos ao acaso, com oito repetições, em esquema fatorial 10 x 2, com dez tratamentos de herbicidas, com ou sem a aplicação de glyphosate em pós-emergência. Os dez tratamentos de herbicidas foram chlorimuron-ethyl (10 e 15 g ha-1), diclosulam (16,8 e 25,2 g ha-1), sulfentrazone (200 e 300 g ha-1), flumetsulam (60, 78 e 140 g ha-1), além de uma testemunha sem herbicida mantida sem plantas daninhas. A aplicação dos herbicidas em pré-emergência ocorreu um dia após a semeadura da soja V-MAX RR (NK-7059). A aplicação de glyphosate a 1200 g ha-1 foi feita 21 dias após a emergência da soja (V3). Os resultados mostraram que os herbicidas aplicados em pré-emergência afetaram o desenvolvimento inicial da soja, ocorrendo redução no crescimento das plantas e sintomas de fitointoxicação. Porém, de modo geral, isto não refletiu na produtividade de grãos. Os únicos tratamentos de herbicidas considerados não seletivos para a soja foram aqueles nos quais se aplicou flumetsulam (78 e 140 g ha-1) em pré-emergência, seguidos da aplicação de glyphosate em pós. Com essas combinações, houve redução na produtividade de grãos.

In weed management systems, the application of pre-emergence herbicides is an interesting option,since they are an important tool in the management of resistant populations. This study aims to evaluate the selectivity of herbicides applied in pre-emergence soybean, combined or not with glyphosate post-emergence in clay soil. The experimental design was a randomized blocks with eight replicates in 10 x 2 factorial, ten herbicide treatments, with or without the application of glyphosate post-emergence. The herbicide treatments were chlorimuron-ethyl at 10 and 20 g ha-1; diclosulam at 16.8 and 25.2 g ha-1; sulfentrazone at 200 and 300 g ha-1; flumetsulam at 60, 78 and 140 g ha-1, and a check without herbicides kept free of weeds. The application of herbicides pre-emergence came a day after the planting of soybeans V-MAX RR (NK-7059), and the application of glyphosate at 1200 g ha-1 occurred 21 days after soybean emergence (V3). The results showed that herbicides applied pre-emergence affected the early development of soybeans, with reduction in plant height and visual symptoms of crop injury. But overall, this was not reflected in grain yield. The only herbicide treatments considered non-selective for soybeans were those in which flumetsulam (70 and 140 g ha-1) was applied in pre-emergence, followed by application of glyphosate post-emergence. With these combinations, there was a reduction in grain yield.

Alternativas para o controle de soja RR® voluntária na cultura do algodoeiro / Alternatives for the control of voluntary soybean RR® in cotton crop

Com o advento do cultivo de algodão em segunda safra, o controle de plantas voluntárias de soja RR® tornou-se uma operação indispensável na cotonicultura. Assim, o presente trabalho teve por objetivo avaliar a eficiência de diferentes alternativas de controle químico de plantas voluntárias de soja RR®, mediante a avaliação de herbicidas empregados no algodão. Foram instalados dois experimentos em casa de vegetação, sendo um com plantas de soja em estádio V1 e o outro em V2. Foram avaliados 21 tratamentos, sendo que estes compostos pela aplicação isolada e em mistura dos herbicidas pyrithiobac-sodium, amonio-glufosinate, glyphosate e trifloxysulfuron-sodium em diferentes doses. As variáveis analisadas foram: controle aos 7 e 28 dias após a aplicação dos herbicidas (DAA); matéria seca e altura das plantas aos 28 DAA. Os resultados demonstraram que nenhuma das misturas entre os herbicidas apresentaram antagonismo no controle de soja RR®. Diferentes níveis de supressão podem ser obtidos pela aplicação dos herbicidas avaliados, porém, apenas o amonio-glufosinate isolado ou associado ao pyrithiobac-sodium controlou todas as plantas voluntárias, independentemente do estádio de aplicação. Em geral, a soja apresentou maior tolerância aos herbicidas testados quando em estádio de crescimento mais avançado.

With the advent of cotton cultivation in the second harvest, the control of volunteer soybean GR® has become an indispensable operation on cotton. So, this study had to evaluate the efficiency of different alternatives to chemical control of volunteer plants RR® soybean, through an assessment of herbicides used in cotton. Two experiments were established in greenhouse, one with soybean plants in stage V1 and the other in V2. There were evaluated 21 treatments, compounds by alone and in mixture of herbicides pyrithiobac-sodium, amonio-glufosinate, glyphosate and trifloxysulfuron-sodium at different rates. The variables analyzed were: control at 7 and 28 days after herbicide application (DAA), dry weight and plant height at 28 DAA. The results showed that none of the mixtures showed antagonism between the herbicides in control of GR® soybeans. Different levels of suppression can be obtained by application of the herbicides evaluated, but, only the amonio-glufosinate, isolated and associated with pyrithiobac-sodium controlled all volunteer plants, regardless of the application stage. In general, soybean was more tolerant to herbicides while in more advanced growth stage.

Selectivity of preemergence herbicide treatments for cotton crop / Seletividade de herbicidas aplicados em pre-emergencia na cultura do algodoeiro

The use of preemergence herbicides in cotton crop is one of the main tools in weed control. However, little is known about the effects of different herbicide tank mixtures on this crop. Therefore, this work was aimed at evaluating the selectivity of herbicides applied isolated or in mixtures to cotton at preemergence. Herbicide treatments included alachlor, s-metolachlor, diuron, prometryn, trifluralin, oxyfluorfen, alachlor+diuron, alachlor+prometryn, s-metolachlor+diuron, s-metolachlor+prometryn, oxyfluorfen+diuron, oxyfluorfen+prometryn, trifluralin+diuron, trifluralin+prometryn, trifluralin+oxyfluorfen. Herbicide treatments did not affect cotton stand. Oxyfluorfen, isolated or in mixture with diuron, prometryn, and trifluralin caused more significant crop injuries than all the other herbicide treatments. However, only oxyfluorfen+diuron, and trifluralin+oxyfluorfen decreased crop yield, and are regarded as presenting lower selectivity to cotton, cv. Delta-Opal.

O uso de herbicidas em pré-emergência da cultura do algodoeiro é uma das principais ferramentas no controle de plantas daninhas. Entretanto, pouco se conhece sobre os efeitos de misturas em tanque de diferentes produtos nessa cultura. Dessa forma, este trabalho teve por objetivo avaliar a seletividade de herbicidas aplicados em préemergência, isolados ou em misturas, na cultura do algodão. Os tratamentos testados foram compostos dos seguintes herbicidas e suas respectivas doses (g a.i. ha-1): alachlor (1440), S-metolachlor (768), diuron (1500), prometryn (1500), trifluralin (1800), and oxyfluorfen (192) aplicados isoladamente, e em mistura formando os seguintes tratamentos: alachlor+diuron (1440+1500), alachlor+prometryn (1440+1500), S-metolachlor+diuron (768+1500), Smetolachlor+prometryn (768+1500), oxyfluorfen+diuron (192+1500), oxyfluorfen+prometryn (192+1500), trifluralin+diuron (1800+1500), trifluralin+prometryn (1800+1500), e trifluralin+oxyfluorfen (1800+192). O experimento foi conduzido por meio de testemunhas duplas. Foram realizadas avaliações relacionadas à fitointoxicação visual, altura de planta, número de maçãs e produção de algodão em caroço. Os tratamentos herbicidas não influenciaram o estande da cultura do algodoeiro. O herbicida oxyfluorfen isolado ou em mistura com diuron, prometryn e trifluralin proporcionaram maior fitointoxicação à cultura em relação aos demais tratamentos. Entretanto, somente oxyfluorfen + diuron e trifluralin + oxyfluorfen apresentaram rendimento inferior à testemunha, sendo considerados, portanto, de baixa seletividade para o cultivar Delta-Opal.

Sorption-desorption of indaziflam in selected agricultural soils.

Indaziflam, a new alkylazine herbicide that inhibits cellulose biosynthesis, is under current development for soil applications in perennial crops and nonagricultural areas. Sorption and desorption of indaziflam in six soils from Brazil and three soils from the United States, with different physical chemical properties, were investigated using the batch equilibration method. Sorption kinetics demonstrated that soil-solution equilibrium was attained in <24 h. The Freundlich equation described the sorption behavior of the herbicide for all soils (R(2) > 0.99). K(f) values of the Brazilian oxisols ranged from 4.66 to 29.3, and 1/n values were ≥ 0.95. Sorption was positively correlated to %OC and clay contents. U.S. mollisol K(f) values ranged from 6.62 to 14.3; 1/n values for sorption were ≥ 0.92. K(f) values from mollisols were also positively correlated with %OC. These results suggest that indaziflam potential mobility, based solely on its sorption coefficients, would range from moderate to low in soil. Desorption was hysteretic on all soils, further decreasing its potential mobility for offsite transport.

Qualidade fisiológica das sementes de soja rr em resposta ao uso de diferentes tratamentos contendo glyphosate em aplicação sequencial / Physiological quality of rr soybean seeds in response to the use of different treatments with sequential glyphosate application

O objetivo do presente trabalho foi avaliar a qualidade fisiológica das sementes da soja RR, sob efeito do manejo com glyphosate em pós-emergência, aplicado em misturas ou isolado, de forma sequencial. O trabalho foi constituído de três experimentos com distintos tratamentos, instalados no ano agrícola 2006/2007, no município de Floraí, PR. O delineamento experimental utilizado foi o de blocos ao acaso, com doze tratamentos e quatro repetições, para cada experimento. A qualidade fisiológica das sementes foi avaliada por meio dos testes de germinação e primeira contagem do teste de germinação. Os resultados demonstraram que a aplicação sequencial de glyphosate isolado e em altas doses influenciou mais a qualidade das sementes de soja RR, do que a aplicação sequencial em mistura com outros herbicidas, como o lactofen e o chlorimuron-ethyl. Não foi constatado efeito negativo sobre a qualidade fisiológicas das sementes, quando das misturas de glyposate com estes herbicidas em pós-emergência.

O objetivo do presente trabalho foi avaliar a qualidade fisiológica das sementes da soja RR, sob efeito do manejo com glyphosate em pós-emergência, aplicado em misturas ou isolado, de forma sequencial. O trabalho foi constituído de três experimentos com distintos tratamentos, instalados no ano agrícola 2006/2007, no município de Floraí, PR. O delineamento experimental utilizado foi o de blocos ao acaso, com doze tratamentos e quatro repetições, para cada experimento. A qualidade fisiológica das sementes foi avaliada por meio dos testes de germinação e primeira contagem do teste de germinação. Os resultados demonstraram que a aplicação sequencial de glyphosate isolado e em altas doses influenciou mais a qualidade das sementes de soja RR, do que a aplicação sequencial em mistura com outros herbicidas, como o lactofen e o chlorimuron-ethyl. Não foi constatado efeito negativo sobre a qualidade fisiológicas das sementes, quando das misturas de glyposate com estes herbicidas em pós-emergência

Sistemas de dessecação antecedendo a semeadura direta de milho e controle de plantas daninhas / Desiccation systems prior to no-till corn sowing and weed control

No sistema de plantio direto, a escolha do momento adequado para a dessecação da cobertura vegetal antecedente à semeadura é fundamental para o êxito da cultura do milho. O objetivo do trabalho foi avaliar os efeitos sobre a cultura do milho de três sistemas de dessecação de manejo antecedendo o plantio direto combinados com três métodos de controle de plantas daninhas, em áreas com alta densidade de infestação de ervas. Os tratamentos foram arranjados em esquema fatorial (3x3) + 1, em delineamento de blocos casualizados, com cinco repetições. Os três sistemas de dessecação avaliados foram: (1) dessecação de manejo realizada imediatamente antes da semeadura - sistema Aplique-Plante ("AP"); (2) dessecação de manejo realizada sete dias antes da semeadura direta (DAS) ("7 DAS"); e (3) manejo antecipado ("MA"), quando as dessecações foram realizadas aos 25 e 1 DAS do milho. Após a emergência da cultura, as opções de controle foram: (1) nenhum controle de plantas daninhas; (2) capina manual e (3) aplicação de mesotrione + atrazine + óleo mineral em pós-emergência, além de uma testemunha sem manejo e sem controle em pós-emergência. Verificou-se que, após a emergência da cultura, a utilização do MA proporcionou maior controle das plantas daninhas, em comparação com os sistemas AP e 7 DAS. Evidenciou-se um atraso de crescimento nas plantas de milho crescidas nas áreas onde foi utilizado o sistema AP. Observou ainda que, independentemente do método de controle de plantas daninhas utilizado em pós-emergência, os maiores rendimentos de grãos de milho ocorreram no MA com ganhos que variaram entre 593 a 1060 kg ha-1.

The adequate timing for cover crop management before sowing is fundamental for the success of no-till corn. This research aimed to evaluate the effects on corn growth and yield of three burndown systems before no-till sowing, combined with three weeds control methods after crop emergence, in areas with high density of weeds. Treatments were arranged in a factorial scheme (3x3) + 1, randomized block design and five replications. The three burndown methods evaluated were: (1) burndown right before crop sowing ("AP"); (2) burndown seven days before crop sowing ("7 DAS"); and (3) antecipated burndown ("MA"), composed of herbicide application, at 25 days and 1 day before crop sowing. After corn emergence, weed control treatments were: (1) no control; (2) manual weeding; and (3) mesotrione + atrazine + mineral oil applied at post-emergence, and an untreated check, with no burndown and no post-emergence weed control. The burndown system MA improved weed control after crop emergence compared to AP and 7 DAS. Delay of corn growth occured in areas where AP burndown was used. Regardless the method of post-emergence weed control, the highest grain yields were registered in MA, with gains from 593 to 1060 kg ha-1.

Bioavailability of diuron, imazapic and isoxaflutole in soils of contrasting textures.

This research was aimed at understanding the dynamics of the herbicides diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], imazapic [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-methylnicotinic acid] and isoxaflutole [5-cyclopropyl-4-(2-methanesulfonyl-4-trifluoromethyl benzoyl)isoxazole] in two soils of different physico-chemical properties. To accomplish such intent, several greenhouse experiments were run. The bioavailability of diuron (0; 1.6 and 3.2 kg ha(-1)), imazapic (0; 98 and 122.5 g ha(-1)) and isoxaflutole (0; 35 and 70 g ha(-1)) was measured in samples from a sandy loam soil and a clay soil, by sowing a bioindicator (Brachiaria decumbens), at 0, 25, 50, 75 and 100 days after herbicides application (DAA). Diuron was very stable in clay soil, providing control equal to or higher than 92% of bioindicator, up to 100 DAA, as assumed by biomass accumulation. No differential effect was observed in sandy loam soil, even when 2x labeled rate were applied. Imazapic provided a short bioavailability in relation to B. decumbens, independent of rates applied. The persistence of isoxaflutole was longer in clay soil (28 to 30 days).

Sorption-desorption of atrazine and diuron in soils from southern Brazil.

The objective of this study was to investigate the behavior of sorption and desorption of the herbicides atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and diuron [3-(3,4-dichlorophenyl)-1,1-dimethyleurea] in soil samples from a typical lithosequence located in the municipality of Mamborê (PR), southern Brazil. Five concentrations of 14C-atrazine and 14C-diuron were used for both herbicides (0.48, 0.96, 1.92, 3.84, and 7.69 mg L(-1)). Sorption of both herbicides correlated positively with the organic carbon and clay content of the soil samples. Sorption isotherms were well described by the Freundlich model. The slope values of the isotherm (N) ranged from 0.84 to 0.90 (atrazine) and from 0.75 to 0.79 (diuron) for the lithosequence samples. Sorption of diuron was high regardless of the soil texture or the concentration added. The desorption isotherms for atrazine and diuron showed good fit to the Freundlich equation (R2 >or= 0,87). Atrazine slope values for the desorption isotherms were similar for the different concentrations and were much lower than those observed for the sorption isotherms. Significant hysteresis was observed in the herbicide desorption. When the two herbicides were compared, it was found that diuron (N = 0.06-0.22) presented more pronounced hysteresis than atrazine. The results showed that, quantitatively, a greater atrazine fraction applied to these soils remains available to be leached in the soil profile, as compared to diuron.

Impact of sublethal doses of 2,4-D, simulating drift, on tomato yield.

Tomato is considered one of the most sensitive crops regarding 2,4-D drift. In many cases, such susceptibility has led to important restrictions in the use of 2,4-D based products. Field experiments were carried out for two consecutive years in tomato, by applying sublethal doses of 2,4-D (ranging from 0.42 to 13.44 g a.i. ha(-1)) directly to plants, at different stages of growth, as a simulation of eventual drifts to the crop. The range of rates was based on the assumption of a 0.0625-2.0% drift level of a 1 L ha(-1) of the most common formulated herbicides. For this crop, the range of rates between 0.42 and 13.44 g a.i ha(-1) applied at the beginning of flowering caused a linear crop reduction. On the other hand, rates < or = 13.44 g a.i. ha(-1) applied after full development of fourth truss stage or latter had no effect on crop yield or development. For tomato, tolerance to 2,4-D strongly increases with plant age.

Sorption kinetics of atrazine and diuron in soils from southern Brazil.

Sorption kinetics of atrazine and diuron was evaluated in soil samples from a typical landscape in Paraná. Samples were collected (0-20 cm) in a no-tillage area from Mamborê, PR, which has been cultivated under a crop rotation for the last six years. Six sampling points of the slope were selected to represent a wide range of soil chemical and physical properties found in this area. Radiolabeled tracers (14C-atrazine and 14C-diuron) were used and the radioactivity was detected by liquid scintillation counting (LSC). Sorption was accomplished for increasing equilibration periods (0.5, 1.5, 3, 6, 12, 24, and 48 h). Kinetics data fitted adequately well to Elovich equation, providing evidences that soil reaction occurs in two distinct stages: a fast, initial one followed by a slower one. During the fast phase, 34-42 and 71-79% of total atrazine and diuron applied were sorbed to soil samples. No important differences were found among combinations of soil and herbicide sorption during the slow phase. The unrealistic conditions under batch experiments should be overestimating sorption in the fast phase and underestimating diffusion in the slow phase. Sorption of both herbicides was positively correlated to organic carbon and clay contents of soils, but atrazine was much less sorbed than diuron, showing its higher potential to contaminate groundwater, specially in sandy, low organic carbon soils.

Rendimento de grãos e qualidade de sementes de soja após a aplicação de herbicidas dessecantes / Grain yield and seed quality of soybean after desiccants application

Aplicaçöes dos herbicidas diquat (0,3kg ha-1), paraquat (0,4kg ha-1), amônio-glufosinato (0,5kg ha-1) e carfentrazone-ethyl (30g ha-1) foram efetuadas em pré-colheita (estádio R7,5) na cultura da soja, com a finalidade de observar os efeitos na produtividade e na qualidade das sementes. Näo houve diferença significativa entre os tratamentos nos testes de germinaçäo, de classificaçäo do vigor de plântula e de sanidade, bem como na massa de cem sementes, no grau de umidade e no rendimento de sementes. No entanto, o glufosinato de amônio e a testemunha sem herbicida apresentaram maiores percentagens de plântulas normais no teste de envelhecimento acelerado, em relaçäo aos demais tratamentos