RESUMO O objetivo deste trabalho foi quantifi car o teor de pigmentos fotossintéticos em biótipos de azevém (Lolium

-The seed bank is characterized by the amount of seeds and other viable reproductive structures in the soil and it is changed by the input and output of seeds, being classified by its permanence in the soil as transient or permanent. The tillage and crops used decisively influence this dynamic and more disturbed areas tend to have richer seed banks. The purpose of this study was to test different soil tillage and crop systems, aiming to reduce or eliminate the ryegrass in the area. The experiment was conducted from 2010 to 2012. In the first year, the effect of chemical tillage was assessed, compared to the area without tillage. From the second year on, in the area that received chemical tillage, the second experiment was installed, where it was assessed the effect of soil tillage and crop rotation in the ryegrass seed yield. The soil tillage treatment was chisel plow and non-chisel plow. The crop rotation was: fallow/ soybean; wheat/soybean; black oat/maize. The samples of soil were taken three times a year and split in 0-5, 5-10, 10-15 and 15-20 cm. After sampling, the seeds were separated from the soil and sterilized. Afterwards, germination and tetrazolium test were conducted. In the same plots used for soil sampling, the emergence flow of ryegrass was assessed in the winter 2011 and 2012. In the first year it was observed that chemical tillage had considerably reduced the amount of ryegrass in the soil. The crop rotations used were more effective than soil tillage in reducing the seed banks in the soil. The rotation oat/maize and wheat/soybean, in only two years, practically zeroed the ryegrass seed banks in the area.Keywords: seed dormancy, chiseling, seeds viability, weeds. de culturas foram: pousio/soja, trigo/soja,[5][6][7][8][9][10][10][11][12][13][14][15] RESUMO -O banco de sementes é composto por sementes e estruturas de reprodução viáveis

-Ryegrass (Lolium multiflorum) is an annual grass, traditionally used as forage that has become weed in crops in the south of Brazil. It has been observed that there are ryegrass biotypes resistant to glyphosate that survive the application of herbicides that inhibit ALS and ACCase. Therefore, the objective was to evaluate the sensitivity of different ryegrass biotypes to glyphosate, iodosulfuron-methyl and clethodim herbicides. The experiment was carried out in a greenhouse, in randomized blocks, in a triple factorial arrangement with three repetitions. Four ryegrass biotypes were used, where: biotype 1 (B1), susceptible to glyphosate; biotype 2 (B2), resistant to glyphosate; biotype 3 (B3) and biotype 4 (B4), biotypes suspected to be resistant to iodosulfuron-methyl. The doses were standardized in 0; 0.25; 0.5; 1; 2; 4 and 8 times the commercial doses of glyphosate (1080 g ha -1 a.i.) and clethodim (96 g ha -1 a.i.). The variables evaluated were control, in a percentage scale, and dry shoot biomass (DSB) of the plants at 28 days after the application of treatments (DAT). With that data, we calculated the parameters of the equation, from which the necessary dose was determined to reduce the DSB in 50% comparing to the non-treated plants (GR50) and the resistance factor (F). Biotypes B2, B3 and B4 obtained Resistance factors (F) above 10 comparing to glyphosate and iodosulfuron-methyl herbicides, B3 being the highlighted biotype because, besides being resistant to those two herbicides, also showed an F value close to the clethodim threshold, which can characterize a low resistance level to this herbicide. All biotypes, except the control one, were resistant to the iodosulfuron-methyl and glyphosate herbicides, which characterizes multiple resistance to those herbicides. The clethodim herbicide can be an alternative for the control of biotypes resistant to glyphosate and iodosulfuron-methyl; however, attention should be paid to the chemical handling of these populations, because we identified biotypes with low resistance level to this herbicide. Keywords: multiple resistance; resistance fator; Lolium multiflorum Resumo -O azevém (Lolium multiflorum) é uma gramínea anual, tradicionalmente utilizada como forrageira que se tornou planta daninha em lavouras no sul do Brasil. Tem-se observado biótipos de azevém, resistentes ao glyphosate, sobrevivendo à aplicação de herbicidas inibidores de ALS e ACCase. Assim, objetivou-se avaliar a sensibilidade de diferentes biótipos de azevém aos herbicidas glyphosate, iodosulfurom-metílico e clethodim. O experimento foi conduzido em casa de vegetação, em blocos casualizados, arranjo fatorial triplo com três repetições. Foram utilizados quatro biótipos de azevém, sendo: B1, suscetível ao glyphosate; B2, resistente ao glyphosate; B3 e B4, biótipos suspeitos de resistência ao iodosulfurom-metílico. As doses foram padronizadas em 0; 0,25; 0,5; 1; 2; 4 e 8 vezes as doses comerciais dos herbicidas glyphosate (1080 g ha -1 e.a.), iodosulfurom-metílico (5 g ha -1 i.a.) e clethod...

Soybean cultivars without tolerance can suffer injury from exposure to tank herbicide residues. This study aimed at assessing the potential effects of the broad spectrum herbicide dicamba on sensitive soybean during its vegetative and reproductive stages. The trial was performed in a randomized complete block design with four replications. Six rates (1.4, 2.8, 5.6, 11.2, 16.8 and 28.0 g ae ha-1) of dicamba were applied at two soybean growth stages (V3 and R2). The soybeans were planted in Passo Fundo, Rio Grande do Sul state in 2015/16 agricultural year. The dicamba induced symptoms of soybean phytotoxicity showed a steady rise at all the assessment times. The soybean decreased in height as the subdose of the herbicide increased. Dicamba was observed to negatively affect the number of nodes alone, during the V3 and R2 stages. The grain yield was adversely affected at the 28.0 g ae ha-1 subdose, in the V3 application stage, and in response to the 16.8 and 28.0 g ae ha-1 subdoses in the R2 stage.

Residues of herbicide tanks may cause damage to sensitive crops. The objective of this study is to evaluate the potential effects of subdoses of the herbicide 2,4-D choline salt on the vegetative and reproductive stages of soybean. The experiment was randomized blocks with a subdivided plot design and four replications. The application times were at V3 and R2 in the main plot. The herbicide 2,4-D choline salt was applied at the subdoses 0, 2.28, 4.56, 9.12, 18.24, 27.36 and 45.60 g a.e. ha-1 in the subplots. Phytotoxicity was evaluated at 3, 7 and 14 days after application (DAT) of treatments, soybean height at 14 and 28 DAT and at ripening, yield components at ripening, and grain yield. The phytotoxicity evaluation of 2,4-D choline salt evidenced that symptoms were only observed up to 14 days after application (DAT) of treatments. The 2,4-D did not affect any of the variables tested. Grain yield was not influenced by application times or subdoses.

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