Variação do tamanho de sementes de plantas daninhas e sua influência nos padrões de emergência das plântulas

Estudos relacionados ao tamanho de sementes e sua influência no processo germinativo de plantas daninhas são necessários devido à grande importância das espécies e à escassez de informações relacionadas à produção de sementes dessas plantas. Dessa forma, este trabalho objetivou estudar a variação do tamanho de sementes de 12 espécies de plantas daninhas e a emergência de duas dessas espécies semeadas em diferentes profundidades. Foi mensurado o peso unitário de 200 sementes por espécie de planta daninha selecionada e estabelecidas curvas de distribuição das frequências não acumuladas para o peso das sementes das espécies, utilizando-se o modelo de Gompertz. Após a classificação por tamanho (pequenas, médias e grandes), sementes de Ipomoea purpurea e Brachiaria decumbens foram semeadas em campo, em canteiros de 1,2 m², em diferentes profundidades no solo (2, 4, 6, 8 e 10 cm) de cada tratamento (profundidade); efetuaram-se quatro repetições. De maneira geral, no primeiro estudo, os resultados indicaram que não há como se referir ao peso de sementes das espécies de plantas daninhas estudadas considerando-se apenas a média dessa característica, devido à variação que pode ser encontrada. Essa grande variação no tamanho das sementes pode estar associada, também, a variações nos padrões de emergência, o que foi verificado no segundo estudo para a espécie I. purpurea. O índice de velocidade de emergência para I. purpurea foi maior para 4 cm de profundidade nas sementes pequenas, 8 cm nas sementes médias e de 6 a 10 cm de profundidade nas sementes grandes.

Suscetibilidade diferencial de espécies convolvuláceas ao flumioxazin determinada através de curvas de dose-resposta

As plantas daninhas denominadas vulgarmente como corda-de-viola, pertencentes aos gêneros Ipomoea e Merremia, estão entre as mais importantes do Brasil. A identificação das espécies em campo, bem como o conhecimento da suscetibilidade específica a herbicidas, notadamente a flumioxazin, cuja tolerância específica é variável, são informações essenciais para uma recomendação racional de manejo. Com o intuito de determinar a suscetibilidade diferencial das convolvuláceas Ipomoea purpurea, Ipomoea hederifolia, Ipomoea triloba, Merremia cissoides e Merremia aegyptia, foram construídas curvas de dose-resposta com o flumioxazin, para obtenção dos controles percentuais de 50, 80, 95 e 99. Para isso, foram conduzidos dois experimentos em casa de vegetação; para cada espécie de planta daninha, os tratamentos herbicidas foram: 0, 7,81, 15,63, 31,25, 62,5, 125, 250, e 500 g de flumioxazin ha-1, aplicados em condições de pré-emergência. A partir dos resultados, conclui-se que a suscetibilidade ao flumioxazin, em ordem decrescente, é: Merremia aegyptia < Ipomoea hederifolia < Ipomoea triloba < Ipomoea purpurea < Merremia cissoides. As doses que proporcionam 80% de controle são, respectivamente pela ordem de espécies, de 238,6; 173,1; 84,7; 43,8; e 16,8 g de flumioxazin ha-1. Merremia aegyptia não é satisfatoriamente controlada pelo flumioxazin.

Efeito da chuva na eficiência de herbicidas aplicados em pós-emergência sobre corda-de-viola

O objetivo deste trabalho foi avaliar a influência da chuva na eficiência de herbicidas aplicados em pós-emergência em plantas de Ipomoea grandifolia. As plantas de I. grandifolia foram cultivadas em vasos plásticos com capacidade de 2,5 L, em casa de vegetação, com uma planta por vaso. O delineamento experimental utilizado foi o inteiramente casualizado, com quatro repetições, com os tratamentos dispostos em um esquema fatorial 7x8 (sete tratamentos químicos e oito períodos para ocorrência de chuva após a aplicação dos tratamentos). Os tratamentos químicos constaram da aplicação de glyphosate em cinco formulações comerciais (Roundup Original, Roundup WG, Roundup Transorb, Roundup Transorb R e Roundup Ultra) a 1.080 g e.a. ha-1, amônio-glufosinate (Finale) a 400 g i.a. ha-1 e 2,4-D (DMA 806) a 1.000 g e.a. ha-1 e de oito intervalos de tempo para simulação de uma chuva de 15 mm, com duração de cinco minutos: 15', 30', 1h, 2h, 4h, 6h, 8h após a aplicação dos tratamentos e uma testemunha sem chuva, Foram realizadas avaliações visuais de controle das plantas aos 7, 14, 21, 28 e 35 dias após a aplicação e, por ocasião da última avaliação, determinou-se a massa seca das plantas. A ocorrência de chuvas após a aplicação de 2,4-D não alterou a sua eficiência no controle das plantas de I. grandifolia; já os herbicidas amônio-glufosinate e glyphosate, em todas suas formulações testadas, apresentaram redução na eficiência de controle quando da ocorrência de chuvas em até oito horas após a aplicação dos tratamentos.

Glyphosate translocation in herbicide tolerant plants

The objective of this study was to evaluate glyphosate translocation in glyphosate-tolerant weed species (I. nil, T. procumbens and S. latifolia) compared to glyphosate-susceptible species (B. pilosa). The evaluations of 14C-glyphosate absorption and translocation were performed at 6, 12, 36 and 72 hours after treatment (HAT) in I. nil and B. pilosa, and only at 72 HAT in the species T. procumbens and S. latifolia. The plants were collected and fractionated into application leaf, other leaves, stems, and roots. In S. latifolia, approximately 88% of the glyphosate remained in the application leaf and a small amount was translocated to roots at 72 HAT. However, 75% of the herbicide applied on T. procumbens remained in the leaf that had received the treatment, with greater glyphosate translocation to the floral bud. It was concluded that the smaller amount of glyphosate observed in S. latifolia and T. procumbens may partly account for their higher tolerance to glyphosate. However, I. nil tolerance to glyphosate may be associated with other factors such as metabolization, root exudation or compartmentalization, because a large amount of the herbicide reached the roots of this species.

Residual herbicides in weed management for glyphosate-resistant soybean in Brazil

In agricultural production systems where the glyphosate-resistant soybean crop (Glycine max) is grown and the practice of crop rotation with alternative herbicides is not adopted, the exclusive and continuous use of glyphosate has led to the occurrence of resistant weed populations that may limit or compromise the benefits of this technology. Thus, the efficacy of weed management programs, including the use of residual herbicides (sulfentrazone, flumioxazin, imazethapyr, diclosulan, chlorimuron and s-metolachlor) applied in preemergence and followed by in-crop postemergence applications of glyphosate (PRE-POST) were compared to glyphosate postemergence only programs - POST. The study was conducted across nine locations during the 2009/2010 and 2010/2011 growing seasons. PRE-POST programs were efficient in the control of Amaranthus viridis, Brachiaria plantaginea, Bidens pilosa, Commelina benghalensis, Eleusine indica, Euphorbia heterophylla and Raphanus raphanistrum, with the level of control being similar when comparing the program with two applications of glyphosate POST. Some PRE-POST programs were not efficient in controlling Cenchrus echinatus, Ipomoea hederifolia and Ipomoea triloba. Sulfentrazone and diclosulam PRE-POST programs improved the control of Ipomoea triloba compared to sequential applications of glyphosate alone. No significant differences in soybean yield were observed between any of the herbicide treatments or study locations. The use of residual herbicides in preemergence followed by glyphosate in-crop postemergence provides consistent weed control and reducing early season weed competition. Furthermore, these programs utilize at least two herbicide modes of action for herbicide use diversity, which will be needed to stay ahead of resistance build-up, regardless of when weeds may appear.

Chemical control of morning glory as a function of water restriction levels

Among the herbicides recommended for the dry season and registered to sugarcane crop, amicarbazone, isoxaflutole and the association diuron + hexazinone + sulfomethuron-methyl can be highlighted. These are pre-emergence herbicides efficient against broad-leaved weeds. Morning glory causes large losses in infested sugarcane fields by bending the stalks and interfering in harvesting. In this study the effectiveness of pre-emergence herbicides for two species of morning glory (Ipomoea hederifolia and Ipomoea grandifolia) was evaluated. Treatments were arranged in completely randomized factorial design (4 x 7). There were four periods of water restriction (0, 30, 60 and 90 days), seven chemical treatments [diuron + hexazinone + sulfometuron-methyl (1387 + 391 + 33.35 g a.i. ha-1), diuron + hexazinone + sulfometuron-methyl (1507.5 + 425 + 36.25 g a.i. ha-1), diuron + hexazinone + sulfometuron-methyl (1658.25 + 467.5 + 39.87 g a.i. ha-1), diuron + hexazinone + sulfometuron­methyl (1809 + 510 + 43.5 g a.i. ha-1), amicarbazone (1190 g a.i. ha-1), amicarbazone + isoxaflutole (840 + 82.5 g a.i. ha-1)] and a control with no application. At 7, 14, 21 and 28 days after the restoration of moisture, control was visually evaluated. After the final evaluation, the dry mass of morning glories was measured. At 90 days of water restriction, diuron + hexazinone + sulfometuron-methyl was more effective to control I. hederifolia than the amicarbazone + isoxaflutole tank mixture. The four diuron + hexazinone + sulfometuron­methyl doses have reduced morning glory dry mass to zero; whereas treatments with amicarbazone have not. The most effective treatment for morning glory control was diuron + hexazinone + sulfometuron-methyl. This result may be due to a possible synergistic interaction.

Weed interference on growth and yield of transgenic maize

Plants kept under competition tend to modify their morphology to optimize the use of production factors. This study aimed to evaluate the effects of competition between transgenic maize and five weed species on the growth and yield of transgenic maize hybrid. The experiment used a randomized block design with four replicates in a factorial 5 x 2 + 6 scheme consisting of a combination of maize under competition with five weed species (Bidens pilosa, Commelina benghalensis, Brachiaria brizantha, Sorghum arundinaceum and Ipomoea triloba) in two weed densities (15 or 30 plants m-2) plus six treatments corresponding to maize and weed species without competition. All the means for dry matter accumulated by maize plants in the stem and leaf in the density of 15 plants m ² were higher than the means for plants in coexistence with 30 plants m-². Number of kernels, diameter and length of cob were not affected by competition with weeds. The weeds that most interfered with maize biomass production were S.arundinaceum and B.brizantha. Leaf dry mass accumulation was more sensitive than the production of stem. It was observed that maize was usually very competitive with weeds, and there was a strong decrease in dry matter accumulation of all the weeds in the study when in coexistence with the crop.

Controle de plantas daninhas pelo indaziflam em solos com diferentes características físico-químicas

No solo, os herbicidas estão sujeitos a processos de degradação e sorção, que regulam seu destino e sua disponibilidade. Objetivou-se com este trabalho avaliar a eficiência do indaziflam no controle de cinco espécies de plantas daninhas em três solos com características físico-químicas contrastantes. O experimento foi conduzido em casa de vegetação, no delineamento de blocos ao acaso, arranjado em esquema fatorial 6 x 3 x 5, com quatro repetições. Os tratamentos constaram de seis doses de indaziflam (0, 30, 60, 90, 120 e 150 g i.a. ha-1), três solos (texturas areia, argila e franco-argiloarenosa) e cinco espécies daninhas (Rottboellia cochinchinensis, Panicum maximum, Digitaria horizontalis, Euphorbia heterophylla e Ipomoea grandifolia). O solo foi peneirado e colocado em bandejas perfuradas, e as espécies, semeadas a 0,015 m de profundidade. O herbicida foi aplicado sobre solo úmido, e as bandejas, colocadas sob irrigação diária de 5 mm, aproximadamente. Avaliou-se a emergência, sete dias após a emergência, e o controle das espécies, 40 dias depois da aplicação. O indaziflam foi mais eficiente no controle das espécies D. horizontalis, P. maximum e R. cochinchinensis. As duas primeiras foram muito sensíveis ao herbicida, com controle total dessas espécies em todas as doses e solos testados. No solo argiloso, R. cochincinensis só foi eficientemente controlada a partir da dose de 50 g ha-1 de indaziflam. O controle de E. heterophylla e I. grandifolia pelo indaziflam foi mais eficiente no solo franco-argiloarenoso.

Effects of straw decomposition degree on leaching and weed control efficacy of tebuthiuron and hexazinone in green sugarcane harvesting

Green sugarcane harvesting may promote great changes in the dynamics of herbicides in the environment. Our goal was to evaluate the influence of straw decomposition degree on leaching and weed (Ipomoea grandifolia) control efficacy by (14C) tebuthiuron and hexazinone. The presence of straw on the soil surface affected leaching, mainly for hexazinone (leaching reduced from 37 to 5% of the applied amount in the presence of straw). Overall, tebuthiuron showed more efficient control of Ipomoea than hexazinone. The straw decomposition degree affected only hexazinone efficacy that was lowest for the least decomposed straw. Further studies are needed to evaluate the effects of sugarcane straw on herbicides dissipation, particularly on volatilization and photolysis, to better predict their efficacy and environmental fate.

Weed mapping using techniques of precision agriculture

The aim of this study was to identify and map the weed population in a no-tillage area. Geostatistical techniques were used in the mapping in order to assess this information as a tool for the localized application of herbicides. The area of study is 58.08 hectares wide and was sampled in a fixed square grid (which point spaced 50 m, 232 points) using a GPS receiver. In each point the weeds species and population were analyzed in a square with a 0.25 m2 fixed area. The species Ipomoea grandifolia, Gnaphalium spicatum, Richardia spp. and Emilia sonchifolia have presented no spatial dependence. However, the species Conyza spp., C. echinatus and E. indica have shown a spatial correlation. Among the models tested, the spherical model has shown had a better fit for Conyza spp. and Eleusine indica and the Gaussian model for Cenchrus echinatus. The three species have a clumped spatial distribution. The mapping of weeds can be a tool for localized control, making herbicide use more rational, effective and economical.

INFLUENCE OF PRECIPITATION AND SUGARCANE STRAW IN AMINOCYCLOPYRACHLOR AND INDAZIFLAM CONTROL EFFICIENCY

ABSTRACTThe raw sugarcane harvesting system has changed the dynamics of weed tillage for this crop, changing the predominant weed species and providing a barrier between the herbicide and the soil. Thus, this study has aimed to assess the influence of precipitation and sugarcane straw in the aminocyclopyrachlor and indaziflam herbicides control efficiency for the species Ipomoea trilobaand Euphorbia heterophylla. There were two trials, one for aminocyclopyrachlor and one for the indaziflam, both in the greenhouse at the campus of Faculdade Integrado in the Brazilian city of Campo Mourão, PR. Each experiment consisted of eight treatments with four replications. The treatments consisted of the combination of the presence of straw (10 t ha-1), capillary irrigation and rainfall simulation (20 mm). Assessments of control percentage of I.triloba and E.heterophylla were carried out, as well as the number of plants per pot. The aminocyclopyrachlor and indaziflam herbicides applied directly to the soil were efficient in controlling these species. The 20 mm rainfall simulation or daily irrigation on the straw are indispensable to promote the removal of aminocyclopyrachlor and indaziflam from the straw and provide satisfactory control of I.triloba and E.heterophylla.

Soybeans Competitiveness with Morning Glory

Weeds interfere negatively on development, yield and quality of soybeans (Glycine max). Inadequate weed control by herbicide use can select for resistant or tolerant biotypes, leading to a shift in the weed flora. An example is the increase of incidence of morning glory (Ipomoea spp.) in soybeans growing areas in South Brazil. The aim of this study was to determine the competitiveness of soybeans intercropped with I. triloba, I. indivisa and I. purpurea through a replacement experiments series. Greenhouse experiments were conducted in a completely randomized design with four replications. The first experiment was carried out aiming to get the plant population while total plant dry mass remained constant. Other experiments were done under replacement series experiments with soybeans and morning glory ratios of 100:0, 75:25, 50:50, 25:75 and 100:0 using the 250 plant m-2 defined by the preliminary experiment. Leaf area, root and shoots dry mass were assessed. Diagrams along with index interpretation were used to performed a competitiveness analysis. Soybeans showed greater competitiveness as I. triloba, I. purpurea and I. indivisa species for the leaf area, root and shoots dry mass variables. Intraspecific competition prevails between soybean plants whilst interspecific competition prevails for morning glory.

Efeitos alelopáticos de extratos aquosos de Crinum americanum L.

Investigamos a ação de extratos aquosos de Crinum americanum L. sobre a germinação e crescimento inicial de Lactuca sativa L., Sesamum indicum L. e Raphanus sativus L. e das espécies invasoras: Echinochloa crusgalli (L.) P. Beauv., Ipomoea grandifolia (Dammer) O'Donell e Bidens pilosa L. Preparamos os extratos aquosos a partir de exemplares de um estuário cego em Caraguatatuba, São Paulo. Montamos controles osmóticos com PEG 6000. Analisamos os dados de germinação com Kruskal-Wallis e pós-teste de Dunn, e os dados de crescimento inicial com ANOVA e pós-teste de Tukey. Para todas as espécies testadas obtivemos diminuição na porcentagem e no crescimento inicial e aumento do tempo médio da germinação. O controle osmótico indicou pouca influência da osmolaridade na germinação. Concluímos que C. americanum possui potencial alelopático sobre as espécies testadas.

Studies on ATP-diphosphohydrolase nucleotide-binding sites by intrinsic fluorescence

Potato apyrase, a soluble ATP-diphosphohydrolase, was purified to homogeneity from several clonal varieties of Solanum tuberosum. Depending on the source of the enzyme, differences in kinetic and physicochemical properties have been described, which cannot be explained by the amino acid residues present in the active site. In order to understand the different kinetic behavior of the Pimpernel (ATPase/ADPase = 10) and Desirée (ATPase/ADPase = 1) isoenzymes, the nucleotide-binding site of these apyrases was explored using the intrinsic fluorescence of tryptophan. The intrinsic fluorescence of the two apyrases was slightly different. The maximum emission wavelengths of the Desirée and Pimpernel enzymes were 336 and 340 nm, respectively, suggesting small differences in the microenvironment of Trp residues. The Pimpernel enzyme emitted more fluorescence than the Desirée apyrase at the same concentration although both enzymes have the same number of Trp residues. The binding of the nonhydrolyzable substrate analogs decreased the fluorescence emission of both apyrases, indicating the presence of conformational changes in the neighborhood of Trp residues. Experiments with quenchers of different polarities, such as acrylamide, Cs+ and I- indicated the existence of differences in the nucleotide-binding site, as further shown by quenching experiments in the presence of nonhydrolyzable substrate analogs. Differences in the nucleotide-binding site may explain, at least in part, the kinetic differences of the Pimpernel and Desirée isoapyrases.

Mycoflora and aflatoxigenic species in derivatives of milled rice

Thirty samples of rough rice stored for 6, 12 and 24 months in government authorized warehouses of the state of Rio Grande do Sul, Brazil, were simultaneously collected. After milling of the product, 90 samples (30 of polished rice, 30 of rice bran and 30 of rice hull) were evaluated for their mycoflora, aflatoxigenic species and aflatoxin contamination. The following fungi, listed in decreasing order of frequency, were isolated on Potato-Dextrose Agar: Aspergillus spp., Nigrospora spp., Penicillium spp.; Fusarium spp.; Mucor spp.; Cladosporium spp.; Trichosporon spp. and non-sporulated fungi. The degree of fungal contamination (colony forming units per gram of product) was lowest in polished rice, increasing progressively in samples of rice bran and rice hull. Among the Aspergillus species, A. flavus and A. candidus were isolated most frequently. Of the A. flavus isolates, 52.6% strains were found to be toxigenic and produced only Group B aflatoxins. Analysis of the 90 samples did not reveal the presence of aflatoxins in the rice derivatives.