A. M. Brighenti

Resistência de amendoim - bravo aos herbicidas inibidores da enzima ALS

One of the most efficient methods of weed control in agriculture is the use of selective herbicides. However, repetitive use of the same herbicide or herbicides having the same mechanism of action, has led to the appearance of weed biotypes which have developed resistance. Thus, an experiment was carried out at Embrapa Soja, in Londrina, Parana State, Brazil, in order to confirm whether or not there has been resistance of the weed E. heterophylla to the ALS inhibitor herbicides which had been sprayed for several years in a soybean field where the grower has observed failure of the weed control by the ALS inhibitor herbicides. The suspected resistant plants (E-298) from Cafelândia county, Parana, Brazil, were treated with various doses of several herbicides, compared to a known susceptible biotype. The herbicides and its doses were cloransulan 0,0; 0,015; 0,03; 0,06; 0,12; 0,24 kg a.i./ha, plus Agral 0,2% v/v, imazetaphapyr 0,0; 0,05; 0,1; 0,2; 0,4 e 0,8 kg a.i./ha, imazaquin 0,0; 0,075; 0,15; 0,3; 0,6; 1,2 kg a.i./ha, plus Assist 0,3% v/v, sulfentrazone 0,0; 0,3; 0,6; 1,2; 2,4; 4,8 kg a.i./ha, plus Assist 0,3% v/v and lactofen 0,0; 0,082; 0,165; 0,33; 0,664; 1,329 kg a.i./ha.The results indicated different patterns of cross resistance to cloransulan, imazethapyr and imazaquin; and the GR50 ratios were 97.74; 11.90 and 10.86, respectively. The dose response curves of the resistant biotype presented lower values than the susceptible biotype in all the studied rates for the herbicides cloransulan, imazethapyr and imazaquin. On the other hand, there was no difference in the control between the resistant and susceptible biotypes when sulfentrazone and lactofen were sprayed. It was observed efficient control, mainly with the highest rates of both herbicides, proving that there is no multiple herbicide resistance of the wild poinsettia studied.

Períodos de interferência de plantas daninhas na cultura do girassol

Two experiments were carried out at Embrapa Soybean, Londrina, Paraná Brazil, to evaluate the effect of different periods of control or coexistence of weeds on sunflower crop, considering oil yield and seed yield. The experimental design was completly arranged in randomized blocks, with four replicates. The treatments for both experiments were maintaining the crop either with or without weeds for 7, 14, 21, 28, 42, 49, 56, 70, 84 and 118 days after crop emergence (DAE), during the entire cycle. The weed comunity was composed by hairy beggarticks (Bidens subalternans) and volunteer wheat. Weed densities and dry matter weight were determined, as well as oil yield and grain yield. Weed presence caused a yield daily loss of 1.1 and 2.5 kg ha-1 of oil yield and seed yield, respectively, whereas weed absence provided a daily gain of 6.5 kg ha-1 for oil yield and 14.4 kg ha-1 for seed yield. Weed crop coexistence for up to 21 DAE did not cause any negative effect on oil and seed yields, and the maximum length of time in which the weeds had to be controlled to prevent crop yield losses was 30 days after emergence. The critical period of interference was from 21 to 30 DAE.

Competição relativa de espécies de plantas daninhas com dois cultivares de soja.

An experiment was carried out to evaluate the relative weed species competition with two soybean cultivars of different maturation times, Embrapa-48 (precocious) and Embrapa-62 (median cycle), in Londrina, Parana, Brazil in 1998/99. Four weed species were compared: wild poinsettia (Euphorbia heterophylla), alexander grass (Brachiaria plantaginea), morning glory (Ipomoea grandifolia) and sicklepod (Senna obtusifolia), adjusted to the weed densities of zero, 15, and 30 plants m-2. The experiment was a randomized block design, in sub plots in a 4x3x2 factorial, with four replications. Soybeans and weeds emerged almost simultaneously. Both cultivars responded similarly to competition regarding yield. Productivity of Embrapa-48 was 2,819 kg ha-1 and of Embrapa-62 was 2,565 kg ha-1, with no weed competition. Relative intensity of competition between weed species and soybeans were: B. plantaginea (0.35) < I. grandifolia (0.59) < E. heterophylla (0.61) < S. obtusifolia (1.00). The estimated soybean yield losses (Y%) were accomplished by linear regression/cultivar per plant m-2: B. plantaginea (YE48 = -1,47; YE62 = -1,58; I. grandifolia (YE48 = -2,51; YE62 = -2,67), E. heterophylla (YE48= 2,47; YE62 = -2,83) and S. obtusifolia (YE48 = -4,52; YE62 = -4,21). Soybean yield loss equation adjustments to weeds are discussed.

Weed seedbank dynamics under different soil management systems

Um experimento foi conduzido em campo no periodo de 1982 a 1998, em Londrina-PR, com o objetivo de avaliar o efeito de diferentes sistemas de manejo de solo nas reducoes anuais de um banco de sementes de plantas daninhas e seus periodos de sobrevivencia, sendo as plantas daninhas manejadas atraves de herbicidas, e a sequencia anual de cultivo soja apos trigo. Os tratamentos de manejo de solos foram: 1) semeadura direta; 2) arado de discos e grade niveladora; 3) grade aradora e grade niveladora; 4) escarificacao e grade niveladora. O delineamento experimental foi o de blocos ao acaso, com quatro repeticoes. A identificacao e contagem das sementes presentes no solo foram feitas em 1990, 1995 e 1998. As estimativas de sobrevivencia (a 1% da populacao inicial) das gramineas capim-marmelada (Brachiaria plantaginea) e capim-colchao (Digitaria horizontalis ), nos quatro sistemas de manejo, foram de 5 a 10 anos e 5 a 7 anos, respectivamente; as das especies de folhas largas, como caruru (Amaranthus spp.), de 5 a 9 anos, carrapicho-de-carneiro (Acanthospermum hispidum ), de 7 a 9 anos, de 10 a 20 anos, e picao-preto (Bidens pilosa), de 3 a 4 anos, e a comelinacea trapoeraba (Commelina benghalensis) de 10 a 20 anos. As sementes de especies de plantas daninhas apresentaram caracteristicas distintas de sobrevivencia, em funcao do manejo do solo, do controle ao longo dos anos e das caracteristicas morfologicas e fisiologicas das sementes.

Biologia e manejo do Cardiospermum halicacabum

Biology studies and balloonvine (Cardiospermum halicacabum) management were carried out at Embrapa Soybean, Londrina, Parana, Brazil. Four experiments were conducted under field and greenhouse conditions. The first experiment evaluated growth, development and nutrient demands of the balloonvine plants. The second was conducted under field conditions with balloonvine seeds sowed at several depths to evaluate the capacity of plant emergence. The two other experiments were carried out under greenhouse conditions to evalaute herbicide effectiveness in controlling this species. The highest dry matter accumulation was, in decreasing order, in the stem, leaf and root. Balloonvine presented the following decreasing sequence of nutrient recruitment: N, K, Ca, Mg, S and P. The emergence of balloonvine seedlings occurred from several depths of sowing, including seeds on soil surface up to 12 cm. The treatments 2,4-D (1005 g a.e. ha-1), paraquat (400 g a.i. ha-1), glufosinate-ammonium (300 g a.i. ha-1), lactofen (144 g a.i. ha-1), carfentrazone-ethyl (12 g a.i. ha1), sulfentrazone (600 g a.i. ha-1) and glyphosate (960 g a.i. ha-1) were efficient in controlling balloonvine up to four leaves.

Chemical Interactions of Brachiaria plantaginea with Commelina bengalensis and Acanthospermum hispidum in Soybean Cropping Systems

Previous results obtained in soybean–wheat rotations under no-tillage conditions showed reductions in the seedbank of the weed species Commelina benghalensis, but no alteration in the seedbank of Acanthospermum hispidum in areas infested with Brachiaria plantaginea. Analyses of the soluble fraction of B. plantaginea indicated the predominance of aconitic acid (AA) among the aliphatic acids and ferulic acid (FA) among the phenolic acids. Laboratory bioassays using C. benghalensis and A. hispidum were carried out to evaluate phytotoxic effects of pure organic acid solutions and dilute extracts of B. plantaginea on seed germination, root development, and fungal germination. Solutions of AA and FA were prepared at 0.25, 0.50, and 1.0 mM. Extracts of B. plantaginea were diluted to obtain concentrations of AA similar to those in the prepared solutions. Seeds were sown on 0.5% agar (containing AA, FA, or diluted extract) in plastic-covered receptacles and maintained in a germination chamber for 10 days. AA and FA solutions and the B. plantaginea extract reduced germination and root length, mainly of C. benghalensis. AA also stimulated the development of endophytic fungi (Fusarium solani), which had complementary adverse effects on C. benghalensis germination. FA and AA may play important roles in reducing the seedbank of some weed species, acting directly on germination and development and, indirectly, by stimulating endophytic fungi that alter germination.

Amostragem do banco de semente e flora emergente de plantas daninhas

O objetivo desta pesquisa foi determinar o numero de amostras necessarias para estimar com precisao aceitavel a quantidade de sementes no solo e a flora de plantas daninhas emergentes, em areas experimentais e de lavoura, para auxiliar na tomada de decisao das estrategias de manejo das plantas daninhas. A amostragem do solo para quantificacao do banco de sementes foi feita com trado tubular de 5,0 cm de diâmetro, na profundidade de 0 a 10 cm. A flora emergente foi contada por meio de um gabarito de ferro nas dimensoes de 0,5x0,5 m, de forma aleatoria na area. O numero de amostras necessario foi estimado em razao da media de sementes da amostra, para uma determinada precisao (CV = 20% ou 40%). Foi estimado que, nas areas experimentais, para medias de 10 a 20 sementes/amostra de solo (500 a 1.000 sementes/m2) e coeficiente de variacao de 20%, sao necessarias entre 40 e 90 amostras, respectivamente; com 40% (menor precisao), entre 10 e 20 amostras. Considerando o mesmo intervalo em areas de lavoura, representativas de glebas homogeneas, o tamanho de amostragem necessaria e cerca de tres vezes maior. Levantamentos da flora daninha emergente apresentam menor associacao dos dados (media e variância) entre si, portanto, sao menos apropriados para decisoes de manejo.

Relações entre germinação de sementes de espécies de plantas daninhas e uso da condutividade elétrica

Experiments were carried out under laboratory conditions to determine relationships between weed seed germination and electrical conductivity (EC). Recently-picked seeds of Euphorbia heterophylla, Acanthospermum hispidum, Ipomoea grandifolia, Sida rhombifolia, Bidens pilosa and Commelina benghalensis were used. The seeds were soaked in water for periods of six up to 48 hours, at 20 oC, to determine EC and water absorption levels and placed to germinate. The highest germination levels, for seeds soaked in water for 24 h, were obtained for B. pilosa(88%), E. heterophylla and S. rhombifolia (30%) and the lowest levels were obtained for I. grandifolia (5%), A. hispidum (4%) and C. benghalensis (3%). The weeds tested tend to germinate totally with a soaking periods > six hours, while water absorption tends to increase with CE tending not to accompany absorption levels at the end of longer periods. Further studies must be conducted on the use of electrical conductivity, what may provide an effective and faster evaluation of the dynamics of weed seed banks under a farming system.

Resistência cruzada da losna-branca (Parthenium hysterophorus) aos herbicidas inibidores da enzima acetolactato sintase

Weed control using herbicide application is a common agricultural practice. However, the application of the same herbicide or herbicides with the same mechanism of action, for consecutive years, in the same area, can result in the selection of herbicide resistant biotypes. The aim of this work was to confirm the resistance of a ragweed (Parthenium hysterophorus) biotype to acetolactate synthase (ALS) inhibiting herbicides. The plants were collected on a farm in Mandaguari, north of Parana State, Brazil. Plants with suspicious resistance were treated with several herbicides and rates and compared with those of a susceptible population. The herbicide treatments were established considering the recommended rates, double and four times higher than the recommended rate as follows: cloransulam-methyl 0.0, 33.6, 67.2 and 134.4 g a.i. ha-1 plus adjuvant 0.2% v/v, chlorimuron-ethyl 0.0, 20.0, 40.0 and 80.0 g a.i., imazethapyr 0.0, 100.0, 200.0 and 400.0 g a.i. ha-1, iodosulfuron-methyl-sodium plus foramsulfuron 0.0, 3.0 + 45.0 ga.i. ha-1 (150.0 g c.p. ha-1), 6.0 + 90.0 g a.i. ha-1 (300.0 g c.p. ha-1) and 12.0 + 180.0 g a.i. ha1 (600.0 g c.p. ha-1). In addition, a treatment with 2,4-D (536.0 g a.e. ha1) was applied. Resistant plant dose-response curves presented lower values when compared to the susceptible population, in all rates and herbicides studied. The ragweed biotype was confirmed as resistant to the ALS inhibiting herbicides. Cross-resistance was observed with herbicides belonging to the chemical groups of imidazolinones (imazethapyr), triazolopyrimidines (cloransulam-methyl), sulfonylureas (chlorimuron-ethyl and iodosulfuron-methyl-sodium plus foramsulfuron). 2,4-D has a different mechanism of action, presenting high values of control, and thus being a management alternative in areas with ragweed resistant population.

Variabilidade no grau de resistência de capim-marmelada (Brachiaria plantaginea) aos herbicidas clethodim, tepraloxydim e sethoxydim

O uso continuado de herbicidas pertencentes a um unico mecanismo de acao resulta em pressao de selecao de biotipos resistentes de plantas daninhas. No Brasil, as primeiras manifestacoes de resistencia foram relatadas com as especies de capim-marmelada (Brachiaria plantaginea), picao-preto (Bidens spp.) e amendoim-bravo (Euphorbia heterophylla). Tem-se verificado que, quando da ocorrencia da resistencia de uma planta daninha a um determinado produto, o problema se estende aos demais produtos que possuem o mesmo mecanismo de acao. Sabe-se, porem, que o grau de resistencia podera variar entre os produtos e, eventualmente, ocorrer resistencia para uns e nao para outros. Com o objetivo de avaliar possiveis diferencas na eficiencia de produtos inibidores da enzima ACCase em biotipos resistentes de capim-marmelada, foram conduzidos dois experimentos em casa de vegetacao em Londrina-PR. Os tratamentos incluiram os herbicidas sethoxydim, clethodim e tepraloxydim, em diferentes doses. No primeiro, as aplicacoes foram realizadas com as plantas no estadio de um a dois afilhos e, no segundo, no estadio de dois a tres afilhos. Embora os tres compostos quimicos atuem na inibicao da enzima ACCase, foi evidenciada elevada diferenca no grau de resistencia do capim-marmelada a esses produtos. Os resultados indicaram que o biotipo considerado resistente ao herbicida sethoxydim foi suscetivel aos produtos clethodim e tepraloxydim.