Spontaneous poisoning by Ricinus communis (Euphorbiaceae) in cattle

The aim of this study is to report cases of spontaneous poisoning of cattle by Ricinus communis (castor beans) in Paraíba, a semiarid region of northeastern Brazil. The cases were observed in 2 herds on neighboring properties in 2013. Clinical signs developed within 6-24 h and consisted of weakness, tachycardia, dyspnea, profuse watery diarrhea, dehydration, depression, instability, cramps, permanent lateral recumbency and death within 48-72 h. Of the 60 cattle at risk, 19 were affected and 14 died. Five fully recovered after the course of 12 days. Three animals were necropsied. The main gross lesions were hemopericardium, hemothorax, pulmonary edema, petechial hemorrhages in the epicardium and endocardium, ecchymoses at the papillary muscles and suffusions on the intercostal muscles. Hemorrhages were also observed in the abdominal cavity, spleen and mucosa of the abomasum and small intestine. The rumen content was liquid with a large amount of castor bean seeds. There were circular, whitish and focally diffuse areas in the liver parenchyma. The main microscopic lesions consisted of multifocal coagulative myocardial necrosis with the presence of mononuclear cell infiltration and varying degrees of bleeding between cardiac muscle fibers. The abomasum and small intestine mucosae and submucosa had mild edema and mononuclear and polymorphonuclear inflammatory cell infiltration. The diagnosis of R. communis was based on the history of plant consumption, clinical signs, pathology of the disease and the presence of large amounts of castor bean seeds in the forestomachs.

Viabilidade do uso de herbicidas em mistura com vinhaça para o controle de plantas daninhas em soqueiras de cana-de-açucar

No presente estudo comparou-se a aplicação de herbicidas em mistura com vinhaça, com aplicação pelo sistema convencional, em soqueira de cana-de-açúcar. Os herbicidas usados foram oryzalin, diuron, 2,4 -D, ametryne e tebuthiuron. A aplicação em mistura com vinhaça foi feita com caminhão-tanque com capacidade para 7000 litros, provido com uma barra de distribuição de vazão controlada. A dose de aplicação foi de 25.000 1/ha. A distribuição dos herbicidas com equipamento convencional foi feita com pulverizador John Bean», provido com 16 bicos «Teeject» 110.04, trabalhando com pressão de 1,4 kg/cm². Usou-se delineamento experimental de blocos casualizados com parcelas subdivididas, com quatro repetições. Pelos resultados obtidos constatou-se que, à exceção do diuron, os demais herbicidas não foram prejudicados quando aplicados com vinhaça. O 2,4-D e a ametryne melhoraram a sua ação no controle de plantas daninhas e seu efeito residual aumentou, quando aplicados em mistura com vinhaça. O tebuthiuron e o oryzalin apresentaram comportamento semelhante no controle das plantas daninhas, nos dois sistemas de aplicação. O diuron aplicado em mistura com vinhaça apresentou resultados altamente negativos no controle das planta daninhas.

Assimilate partitioning and phytotoxicity in soybean plants treated with herbicides

To investigate the effects of trifluralin, chlorimuron and clomazone on morphology and assimilate partitioning during soybean development, plants were grown in a greenhouse and sampled at 14-day intervals. Clomazone reduced stem and leaf dry matter accumulation at 14 days after emergence (DAE), while trifluralin and chlorimuron reduced plant part dry matter accumulation up to 28 DAE. The number of leaves, plant height, mass and number of pods and seeds, and the shoot/root ratio were not influenced by the herbicides. Roots, stems and leaves were the preferred sinks up to the R2 growth stage, while pods and developing seeds became the preferred sinks later. This order was not altered by the herbicides.

Root exudation of imazapyr by eucalypt, cultivated in soil

Imazapyr has been used to control stump sprouting in stand of Eucalyptus plantations, where herbicide is applied to the tree trunk before cutting. The herbicide is applied exclusively on the stump to be killed, but little is known about the final fate of the molecule. Imazapyr exudation via roots of eucalypt grown in soil as the substrate was evaluated under greenhouse conditions. Different herbicide doses (0.000, 0.375, 0.750, 1.125, 1.500, and 3.000 kg ha-1 a.i.) were applied on the aerial parts of 8-month-old Eucalyptus grandis clonal seedlings, cultivated in pots with 18.0 dm³ of soil. Forty days after this treatment, the eucalypt plants were cut and a lateral opening in the containers was made and the plants inclined 90º, with plants sensitive to herbicide presence (sorghum and cucumber) sown into the openings along the exposed soil surface. After 15-day sowing, toxicity symptoms on the shoots as well as the shoot and root system dry biomass of the bio-indicators were evaluated. The results suggest that eucalypt roots do exude imazapyr, and/or its metabolites, at concentrations high enough to cause toxicity to the bio-indicators. Toxicity effects were observed in all plants sown along the exposed soil profile of the container, with higher intensity at higher doses.

Weed control in young coffee plantations through post emergence herbicide application onto total area

This study was carried out to investigate the efficiency of several herbicides under field conditions, by post-emergence application onto the entire area, their effect on the control of weeds in young coffee plantations and commercial coffee and bean intercropping system, as well as on both crops. Seedlings of Coffea arabica cv. Red Catuaí with four to six leaf pairs were transplanted to the field and treated according to conventional agronomic practices. A bean and coffee intercropping system was established by sowing three lines of beans in the coffee inter-rows. At the time the herbicides were sprayed, the coffee plants had six to ten leaf pairs; the bean plants, three leaflets; and the weeds were at an early development stage. Fluazifop-p-butyl and clethodim were selective for coffee plants and controlled only Brachiaria plantaginea and Digitaria horizontalis efficiently. Broad-leaved weeds (Amaranthus retroflexus, Bidens pilosa, Coronopus didymus, Emilia sonchifolia, Galinsoga parviflora, Ipomoea grandifolia, Lepidium virginicum, and Raphanus raphanistrum) were controlled with high efficiency by sole applications of fomesafen, flazasulfuron, and oxyfluorfen, except B. pilosa, C. didymus, and R. raphanistrum for oxyfluorfen. Sequential applications in seven-day intervals of fomesafen + fluazifop-p-butyl, or clethodim, and two commercial mixtures of fomesafen + fluazifop-p-butyl simultaneously controlled both types of weed. Cyperus rotundus was only controlled by flazasulfuron. Except for fluazifop-p-butyl and clethodim, all herbicide treatments caused only slight injuries on younger coffee leaves. However, further plant growth was not impaired and coffee plant height and stem diameter were therefore similar in the treatments, as evaluated four months later. Fomesafen, fluazifop-p-butyl, and clethodim, at sole or sequential application, and the commercial mixtures of fomesafen + fluazifop-p-butyl were also highly selective for bean crop; thus at doses recommended for bean crop, these herbicides may be applied to control weeds in coffee and bean intercropping systems by spraying the entire area.

Effects of weed species competition on the growth of young coffee plants

The effects of competition of seven weed species on the growth of coffee plants were evaluated under greenhouse conditions. Thirty days after coffee seedling transplantation into 12 L pots with soil level area of 6.5 dm², weeds were transplanted into or sown in those pots, at densities of 0, 1, 2, 3, 4 and 5 plants per pot. Competition or weedy periods from weed transplantation or emergence to plant harvesting, at weed pre-flowering stage, were: 77 days - Bidens pilosa, 98 days - Brachiaria decumbens, 180 days - Commelina diffusa, 82 days - Leonurus sibiricus, 68 days - Nicandra physaloides, 148 days - Richardia brasiliensis and 133 days - Sida rhombifolia. Coffee plant height, stem diameter, leaf number and shoot dry matter were determined. Effects of competition by N. physaloides and S. rhombifolia against coffee plants were among the lowest, since only a slight decrease in all the characteristics evaluated in coffee plants was observed. The other weed species caused severe decrease in growth, mainly with increasing weed plant densities. Competition degree was found to depend on weed species and density.

Growth, nodulation, and yield of soybean and associated weeds as affected by weed management

Two field experiments were conducted at the experimental farm of the National Research Centre at Shalakan, Kalubia Governorate, Egypt, during 2006 and 2007 seasons, to study the effect of three pre-emergence herbicides, prometryn [at the rate of 0.75, 1.5 and 2.25 kg ha-1], oxadiargyl [at the rate of 240, 480 and 720 g ha-1] and butralin [at the rate of 1.20, 2.40 and 3.36 kg ha-1], two hand hoeing treatments and a nonweeded check, on weed infestation, nodulation, growth, yield and yield attributes of soybean plants. Two hand hoeing treatments resulted in the highest weed depression expressed as the lowest fresh and dry weights of broadleaved, grassy and total weeds. The reduction percentage in weed dry matter compared to the nonweeded treatment was 98.3, 92.64 and 96.9% in broadleaved, grassy and total weeds, respectively. Application of the three herbicides at higher or recommended doses significantly reduced fresh and dry weight of the weeds compared to the nonweeded treatment. The results indicated that all the three herbicides at rates higher than the recommended markedly decreased the number, fresh and dry weight of nodules as well as root, shoot and total dry weight plant-1, while application of two hand hoeing treatments significantly increased these traits. Two hand hoeing treatments and pre-emergence herbicides at the recommended rates markedly increased soybean yield and its attributes. Two hand hoeing treatments gave the highest values of number of pods per plant-1, weight of pods per plant-1 and number of seeds per plant-1 by 140.7, 150.0 and 59.8%, respectively, compared to the nonweeded treatment. On the other hand, oxadiargyl at the recommended rate (480 g ha-1) was the best treatment for promoting seed yield (g plant-1), seed yield (kg ha-1) and biological yield (g plant-1) compared to the nonweeded treatment by 87.3, 85.0 and 88.2%, respectively. Prometryn at the rate of 1.50 kg ha-1, followed by two hand hoeing treatments, produced the highest shoot and seed protein percentage as well as seed oil percentage, compared to the other weed control treatments.

Perspectives for using light quality knowledge as an advanced ecophysiological weed management tool

The current knowledge of light quality effects on plant morphogenesis and development represents a new era of understanding on how plant communities perceive and adjust to available resources. The most important consequences of light quality cues, often mediated by decreasing in red far-red ratios with respect to the spectral composition of incident sunlight radiation, affecting weed-crop interaction are the increased plant height and shoot to root ratio in anticipation of competition by light quantity, water or nutrients. Although the concepts related to light quality have been extensively studied and several basic process of this phenomenon are well known, little applications of photomorphogenic signaling currently are related to agricultural problems or weed management. The objectives of this review are to describe how light quality change can be a triggering factor of interspecific interference responses, to analyze how this phenomenon can be used to predict weed interference, to reevaluate the critical periods of interference concept, and to discuss its potential contribution towards developing more weed competitive crop varieties. Knowledge on light quality responses involved in plant sensing of interspecific competition could be used to identify red/far-red threshold values, indicating when weed control should be started. Light quality alterations by weeds can affect grain crop development mainly in high yielding fields. Unlike the traditional concept or the critical period of competition, light quality mediated interference implies that the critical period for weed control could start before the effects of direct resource (water, nutrients and available light) limitation actually occur. The variability in light quality responses among crop genotypes and the identification of mutants insensitive to light quality effects indicate that this characteristic can be selected or modified to develop cultivars with enhanced interspecific interference ability. Knowledge on light quality-elicited responses represents a new possibility to understand the underlying biology of interspecific interference, and could be used in the development of new weed management technologies.

Effect of dose and application site on quinclorac absorption by barnyardgrass biotypes

This work aimed to evaluate the uptake and translocation of quinclorac in function of application sites (shoot or roots) by Echinochloa crusgalli biotypes resistant and susceptible to this herbicide. The treatments consisted of quinclorac doses (0; 0.5; 1; 2; 4; 16 and 64 ppm), applied on the shoot or roots of seedlings of barnyardgrass biotypes. The experimental units consisted of plastic cups containing 250 cm³ of sand. The treatments were applied 10 days after emergence, when barnyardgrass plants reached a 2- to 3- leaf growth stage. The barnyardgrass biotypes were irrigated with nutritive solution weekly and maintained for 40 days after emergence, when length, fresh and dry matter of shoot and roots were evaluated. Variance analysis was carried out using the F test at 5% probability, and in case of significance, a non-linear regression analysis was also carried out using a three-parameter logistic model. In the susceptible biotype, quinclorac was more absorbed by the roots than by the shoot. Comparing dry mass production of the different plant parts of the susceptible biotype per application site, it was verified that quinclorac action is higher when applied to the plant roots. However, for the resistant biotype, it was not possible to determine the dose causing 50% reduction in dry mass accumulation (GR50) and in the resistance index (RI) between both biotypes, due to its high resistance to quinclorac (128 times the recommended dosage). The results showed that quinclorac resistance by the evaluated biotype is not due to differences in the absorption site, strongly suggesting that the resistance acquired by the biotype may result from alteration in the target site.

Allelopathic effects of Eucalyptus citriodora on amaryllis and associated grassy weed

A Petri dish assay was carried out for screening different concentrations of aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on germination and seedling growth of wild oat weed (Avena fatua). Seed germination, root and shoot length of wild oat exhibited different degrees of inhibition according to the concentration of the aqueous extract. Maximum inhibitions of germination percentage, root and shoot length were recorded when using 25% fresh leaf extract. Based on this preliminary work (Petri dish assay), studies were conducted under greenhouse conditions at the National Research Center, Egypt, in the two winter seasons of 2006/2007 and 2007/2008 to evaluate the effects of foliar and soil treatments of aqueous extracts of Eucalyptus citriodora fresh and dry leaves on wild oat weed as well as on the growth and flowering of amaryllis (Hippeastrum hybridum), compared with the recommended dose of the herbicide tralkoxydim. Amaryllis fresh and dry weights as well as flowering increased significantly when treated with the previous extracts, especially the fresh leaf extract. However, the fresh and dry weights of wild oat were significantly reduced by the aqueous extracts, either fresh or dry, indicating phytotoxic effects. Tralkoxydim caused complete inhibition of wild oat as compared with the control. The studies involved estimation of the endogenous contents of total phenols in weed. With all the treatments, the inhibitory effects on weeds were correlated with accumulation of the internal contents of total phenols, compared to their respective controls. The amount of phenols correlated well with the weed's growth performance. This study establishes the effect of the aqueous extracts on the weed wild oat, associated with amaryllis, which may serve as a tool in establishing their herbicidal potential.

Competitiveness of alexandergrass or Bengal dayflower with soybean

Weeds compete with field crops mainly for water, light and nutrients, and the degree of competition is affected by the weed density and the intrinsic competitive ability of each plant species in coexistence. The objective of this research was to compare the competitiveness of alexandergrass (Brachiaria plantaginea) or Bengal dayflower (Commelina benghalensis) in coexistence with soybean, cv. M-Soy 8045. A factorial experiment (2 x 5) with two weed species and five competition proportions was carried out in a completely randomized design with four replicates. Proportions were based on a replacement series competition design, always maintaining the total density of four plants per 10 L plastic pots, which corresponded to 60 plants m ². The weed-crop proportions were: 0:4; 1:3; 2:2; 3:1; 4:0; that corresponded to the proportion of 100, 75, 50, 25 and 0% of soybean plants and the opposite for weeds, B. plantaginea or C. benghalensis plants. Leaf area, shoot dry mass of the weeds and soybean and number of soybean trifoliate leaves were evaluated when the soybean reached the phenologic stage of full flowering. B. plantaginea was a better competitor than soybean plants. Otherwise, C. benghalensis revealed a similar competitive ability that of the soybean. In both cases, there were evidences that intraspecific competition was more important.

Effect of crop residues applied isolated or in combination on the germination and seedling growth of horse purslane (Trianthema portulacastrum)

Soil incorporation of crop residues can lead to weed suppression by posing allelopathic and physical effects. Allelopathic potential of the crops sorghum, sunflower, brassica applied as sole or in combination for horse purslane (Trianthema portulacastrum) suppression was evaluated in a pot investigation. Chopped crop residues alone and in combination were incorporated at 6 g kg-1 soil (12 t ha-1), and a weedy check was maintained. Germination traits time to start germination; time to 50% emergence, mean emergence time, emergence index and final germination percentage were negatively influenced by residue incorporation. Crop residues also exerted a pronounced negative influence on the shoot and root length of horse purslane. Significant suppression in leaf and root score and leaf area per plant was also observed. A combination of sorghum and sunflower residues accounted for maximum (71%) seedling mortality. Soil incorporation of allelopathic crop residues can be employed for horse purslane management.

Photosynthetic characteristics of hybrid and conventional rice plants as a function of plant competition

The objective of this work was to evaluate the characteristics related to the photosynthetic ability of hybrid and inbred rice varieties, as a way to assess which of the two presented higher potential to stand out under conditions of competition. The trial was set in a greenhouse in completely randomized block design and 2 x 6 factorial scheme with four replications. Factor A consisted of rice varieties (hybrid or inbred) and factor B by competition levels. Treatments consisted in maintaining one plant of either BRS Pelota (inbred) or Inov (hybrid) variety at the center of the plot, under competition with 0, 1, 2, 3, 4 or 5 plants of the variety BRS Pelota at the periphery of the experimental unit, according to the treatment. Fifty days after emergence (DAE), sub-stomatal CO2 concentration (Ci - mmol mol-1), photosynthetic rate (A - mmol m-2 s-1) and CO2 consumed (DC - mmol mol-1) were quantified, as well as shoot dry mass(SDM).Hybrid plants present higher photosynthesis capacity than inbred plants, when competing with up to 3 times its own density. When under the same competitive intensity, hybrid plants surpass the inbred. However, it should be emphasized that, when in farm condition, the lower competitive capacity with weeds often attributed to the hybrid varieties, probably is due to their lower planting density, but if weed competition is kept at low levels, hybrid rice plants may perform in the same way or usually better than inbred plants.

Weed mapping using a machine vision system

Weed mapping is a useful tool for site-specific herbicide applications. The objectives of this study were (1) to determine the percentage of land area covered by weeds in no-till and conventionally tilled fields of common bean using digital image processing and geostatistics, and (2) to compare two types of cameras. Two digital cameras (color and infrared) and a differential GPS were affixed to a center pivot structure for image acquisition. Sample field images were acquired in a regular grid pattern, and the images were processed to estimate the percentage of weed cover. After calculating the georeferenced weed percentage values, maps were constructed using geostatistical techniques. Based on the results, color images are recommended for mapping the percentage of weed cover in no-till systems, while infrared images are recommended for weed mapping in conventional tillage systems.

Initialism as a mechanism of weed interference: can a crop plant be blinded?

Initialism is a new word proposed to indicate the "shade-avoidance syndrome". Plants detect the presence of neighbor plants very early in the growing season through changes in light quality. They modify the allocation of photosynthesis products privileging shoot growth over the roots. One of the hypotheses of the authors is that, when weed management is timely scheduled, a "blind" crop could be more productive because it would avoid an imbalance on the shoot:root ratio (S:R). Two strategies were developed to test this hypothesis: a) to use the classical Yoda's Law to screen several crops for insensitivity to S:R imbalance; b) to evaluate several growth regulators to control the plant responses to crowding. Experimental results confirm that both strategies can yield insensitive plants. The possibilities of the use of this knowledge are discussed.