Dirceu Agostinetto

Ação de herbicidas sobre mecanismos de defesa das plantas aos patógenos

Plants are required to defend themselves continually against attack by biological agents and also from environmental stresses. Plant immobility and lack of an immunological system like occurs in animals, forced them to develop defence mechanisms, where each cell holds induced defence capacity as well as a pre-formed defence. Such mechanisms can be influenced by herbicide use. The present literature review aims to present the effects of herbicides in plant defence mechanisms to pathogens, as well as to analyse possible consequences of this knowledge on weed and crop management. Some herbicides influence disease severity, inducing or inhibiting phytoalexins synthesis. Herbicides belonging to the diphenylethers chemical group generates of reactive species of oxygen, which intervene in activation of defence genes responsible by the synthesis of phytoalexins and also in hypersensitive response. The use of sublethal glyphosate rates cause opposite effects, decreasing production of phytoalexins and increasing disease severity. Evidence of such effects requires adoption of management strategies in order to reduce their negative impacts or which may benefit from those effects, as can be the case with the use of mycoherbicides.

Monitoramento de agrotóxicos em dois mananciais hídricos no sul do Brasil

The objective of this study was to evaluate and to monitor the presence of pesticides in the waters of the Sao Goncalo channel and the Piratini river located in the southern region of the State of Rio Grande do Sul. During the rice growing season, water samples were collected five times, three samples from the river Piratini and four from the Sao Goncalo canal. The methodology used for the analysis of residues of quinclorac, carbofuran and clomazone was the High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD) and for residues of the pesticides fipronil and betacyfluthrin, the Gas Chromatography with Electron Capture Detection (GC-ECD) was used. Results show that from sowing to harvesting the quantity of pesticide residues in water decreased. It was also observed that, at the lowest point (Laranjal), a greater number of analyses contaminated with residues was detected (11 samples with some type of pesticide). Insecticide carbofuran and herbicide quinclorac were pesticides that presented residues more frequently (16 and 15 times, respectively). Clomazone and fipronil were present in each of the 7 samples with residues and betacyfluthrin was not detected at any site.

ARROZ VERMELHO: ECOFISIOLOGIA E ESTRATÉGIAS DE CONTROLE

Interference caused by red rice (Oryza sativa L.) on cultivated rice (O. sativa L.) is the main factor that limits increasing grain yield potential of the cereal in the state of Rio Grande do Sul, Brazil. This literature review has the objective of describing ecophysiological characteristics of red rice, as well as to discuss strategies that favour cultivated rice in the competition process for environmental resources or that limit its establishment. Due to morphophysiological similarities between both, red rice control cannot be accomplished through the use of selective herbicides alone, requiring the combination of several integrated actions, involving preventive, cultural, physical and chemical methods. The presence of a high red rice population makes rice production impracticable, especially when the field extension turns hand weeding impossible. In such a condition, the most effective methods of control have been: the usage of pre-germinated seeds, early soil preparation combined with no-till seeding, and adaptation of crop rotation.

Competição por recursos do solo entre ervas daninhas e culturas

Engenheiro Agronomo, Aluno do Programa de Pos-graduacao em Fitotecnia, UFRGS.RESUMOA competicao entre plantas e um processo impor-tante tanto em comunidades naturais quanto em ambientes agri-colas. O impacto vegetativo das ervas daninhas em agroecossis-temas e considerado competicao se houver reducao no montantede recursos disponiveis para a cultura e, neste contexto, o desen-volvimento das raizes influencia na competitividade e na sobrevi-vencia das plantas. Uma planta que apresenta sistema radicalbem desenvolvido em extensao e em comprimento tem sido asso-ciada com aumento na habilidade competitiva devido ao maiorpotencial de absorcao de agua e nutrientes. A competicao entreos sistemas radicais das ervas daninhas e das culturas interferetanto na disponibilidade de agua e nutrientes quanto nas intera-coes por luz, na parte aerea. Entretanto, somente ocorrera com-peticao quando a zona de deplecao das raizes da cultura e daservas daninhas se sobreporem. A intensidade de competicao entreraizes das ervas e da cultura pelos recursos abaixo da superficiedo solo dependera do tipo e da disponibilidade dos recursos e daespecie vegetal e de sua capacidade em desenvolver sistemaradical extenso, com diâmetro reduzido e com ampla area super-ficial.Palavras-chave: interferencia, agua, nutrientes, habilidadecompetitiva, sistema radical.SUMMARYCompetition between plants is an important processas much in natural communities as in agricultural environments.The impact of weeds in agroecossystems is refered as competitionif there is a reduction in the amount of resources available for thecrop and, in this context, root development influences plantcompetitivity and survival. A plant which presents a welldeveloped root system in extension and in length has beenassociated with increased competition hability due to a greaterabsorption capacity of water and nutrients. Competition betweenroot systems of weeds and crops interferes in water and nutrientsavailability, as well as in interactions for light in the aerialsystem. However, competition will only occur when depletionzone of crop and weed roots has surpassed themselves. Intensityof competition between roots of weeds and crops by undergroundresources will depend on type and availability of resource, and onplant species, and capacity to develop an extensive root system,with a reduced diameter and a high surface area.Key words: interference, water, nutrients, competitive hability,root system.

Efeitos do manejo mecânico e químico da aveia-preta no milho em sucessão e no controle do capim-papuã

n†The objective of this experiment was to evaluate the effects of mechanical and chemical management of oat straw and of sowing dates of maize after oat desiccation on maize grain yield and on alexandergrass (Brachiaria plantaginea Link) infestation. In 1997/98, treatments were composed by two mechanical management systems of oat (rolled or not) and bare area as the control, by two herbicides (glyphosate and paraquat) applied to desiccate oat straw and by two maize sowing dates after desiccation (one and 15 days). In the 1998/99†growing season, five management systems of oat straw (rolled, cleared and desiccated with glyphosate, glufosinate and paraquat) and a bare area used as check were tested. Delay of maize sowing date in 15 days after oat straw desiccation increased N accumulation, dry matter production per plant and grain yield of maize. Maize grain yield in succession to oat was not influenced by management system of oat straw. Rolling oat straw provided the best control of alexandergrass infestation.

Período crítico para controle de Brachiaria plantaginea em função de épocas de semeadura da soja após dessecação da cobertura vegetal

ABSTRACT - This study was conducted to evaluate the impact of soybean seeding time aftercover crop desiccation on the control of alexandergrass ( Brachiaria plantaginea ) and to quantifythe influence of weed control timing on soybean yield. The experimental design used was asplit-plot, in randomized blocks, with four replications. The treatments consisted of soybeanseeding times (1 and 10 days after desiccant application – DAD), arranged as main plots, andtimes of Alexandergrass control (11, 17, 24, 31, 38, and 45 days after soybean emergence –DAE – for seeding performed 1 DAD, and 8, 15, 22, 29, 36, and 42 DAE for seeding performed10 DAD), arranged as subplots. For each soybean seeding time, a check with Alexandergrasschemical control was included during all crop season. Grass weed control was attained throughapplication of the herbicide clethodim at 120 g ha -1 . Levels of Alexandergrass control, at soybeanharvesting time, varied between 90 and 99%, considering all treatments. There were reductions

Nível de dano econômico como critério para controle de picão-preto em soja

Adoption of the threshold level (TL) concept for weed management evaluates weed populations to implement control measures only when infestations overcome the TL. The objective of this research was to define TL for mixed infestations of Bidens pilosa and Bidens subalternans in the soybean crop. Field experiments were conducted in Passo Fundo and Eldorado do Sul, RS, Brazil. Treatments consisted of mixed densities of the beggartick species and soybean seeding at 3, 7, and 11 days after cover crop desiccation. TL variable values were obtained from 0.4 to 33 beggartick plants m-2. Different responses were obtained for crop-weed interference relations between the two locations evaluated. Delaying soybean seeding in relation to cover crop desiccation increases beggartick interference in this crop. Increases in yield loss per weed unit, in crop yield potential, harvested product value and herbicide efficiency were found to decrease TL values, making control potentially more economic. On the other hand, higher weed control cost increases TL values. It was also verified that seeds produced by non-controlled weeds below TL could compromise adoption of control decision based on this criterion.

Competitividade de cultivares de arroz irrigado com cultivar simuladora de arroz-vermelho

(2) Resumo - Caracteristicas morfologicas e fisiologicas de plantas cultivadas podem afetar sua habilidade competitiva com plantas daninhas. Este trabalho objetivou investigar a competitividade de cultivares de arroz irrigado (Oryza sativa L.) com cultivar simuladora de arroz-vermelho. Investigou-se na safra 2000/2001 o comportamento de oito genotipos de arroz, cultivados na presenca ou ausencia da cultivar de arroz EEA 406, que simulou infestacao de arroz-vermelho. Aos 45 e aos 60 dias apos a semeadura, avaliou-se a resposta da simuladora em relacao as cultivares de arroz. Na colheita, foram determinados estatura de planta, componentes do rendimento e produtividade das plantas. A cultivar tardia IR 841 suprimiu o crescimento da simuladora, apresentando com a cultivar superprecoce Ligeirinho as meno- res reducoes de produtividade quando em competicao. Por sua vez, as cultivares IAS 12-9 Formosa e Bluebelle permitiram maior crescimento e producao de sementes pela concorrente, tambem sofrendo as maiores reducoes de produtividade de graos na condicao de competicao. Termos para indexacao: Oryza sativa, competicao vegetal, planta daninha, manejo da cultura. Competitiveness of flooded rice cultivars with a red rice simulating cultivar Abstract - Morphologic and physiologic characteristics of crop plants can affect their competitive ability with weeds. This research aimed to investigate competitiveness of flooded rice (Oryza sativa L.) cultivars with a red rice simulating genotype. It was investigated, during the 2000/2001 warm season, the behavior of eight rice genotypes, grown in presence or absence of the rice cultivar EEA 406, simulating a red rice infestation. At 45 and 60 days after rice seeding, it was evaluated the response of red rice mimicker genotype in relation to rice cultivars. At harvest, it was determined plant height, yield components, and grain yield of the cultivars. The late season genotype IR 841 suppressed growth of the simulative cultivar, presenting, together with the very-early cultivar Ligeirinho, the lowest reductions in grain yield under competition. In opposite, IAS 12-9 Formosa and Bluebelle cultivars allowed the greatest growth and seed production by the concurrent rice, also presenting the largest decreases of grain yield under the competition condition.

Interferência de picão-preto e guanxuma com a soja: efeitos da densidade de plantas e época relativa de emergência

The objective of this research was to evaluate the effects of hairy beggarticks (Bidens pilosa L.) and arrowleaf sida (Sida rhombifolia L.) densities and relative emergence time, on the degree of interference they may cause on soybeans. There were studies carried out under two conditions in Porto Alegre, RS, Brazil, in 1998/99 and 1999/00. The factors tested were weed species, emergence times, and weed densities. Weedsoybean associations occurred during the vegetative period of the crop. In pot assays, five weed emergence times were evaluated (11, 7, and 2 days before, and 4 and 8 days after soybean emergence). In microplot assays, three weed emergence times were compared in relation to soybeans (4 days before, at the same day, and 4 days after) and six weed densities (0, 4, 8, 16, 32 and 64 plants m -2). It was found that weed relative emergence time, in relation to soybeans, modifies competitive relations between these species, and that beggarticks performs greater competition effects on soybean and is less affected by the crop than is sida. Delay in soybean emergence in relation to weeds increases the negative effects of these species on the crop, which are potentialized by increase in weed density, mainly in presence of beggarticks.

Nível de dano econômico como critério para tomada de decisão no controle de guanxuma em soja

O nivel de dano economico (NDE) e um conceito simples que integra fatores biologicos e economicos que se destina a tornar os resultados de uma tomada de decisao lucrativos para o controle das plantas daninhas. O objetivo deste trabalho foi determinar o NDE para infestacoes de guanxuma (Sida rhombifolia), calculado na base de um unico ano, que justifiquem aplicacao economica de medidas para seu controle na cultura da soja. Foram conduzidos experimentos em campo em Passo Fundo e Eldorado do Sul-RS. Os tratamentos constaram de densidades de guanxuma e de epocas de semeadura da soja em relacao a dessecacao da cobertura vegetal (3, 7 e 11; e 20, 24 e 28 dias apos). Os valores de NDE variaram de 2 a 50 plantas m-2, e os de NDE otimo, de 1 a 6 plantas m-2. Verificaram-se respostas diferentes nas relacoes de interferencia cultura-plantas daninhas entre os ambientes estudados. O atraso na semeadura da soja em relacao a dessecacao da cobertura vegetal incrementa o grau de interferencia de guanxuma na cultura. Constatou-se que as sementes produzidas pelas plantas daninhas nao-controladas, ocorrendo em densidades abaixo do NDE, comprometem a adocao da tomada de decisao de controle com base neste criterio.