G. Concenço

Potencial competitivo de biótipos de azevém (Lolium multiflorum)

The objective of this work was to evaluate the competitiveness of ryegrass biotypes resistant and susceptible to glyphosate, as well as their interference in wheat growth at different densities. At harvesting, 50 days after emergence, tillering, height, and leaf area of ryegrass plants were evaluated and shoot and roots of ryegrass and wheat were collected and their root, stalk and leaf dry mass was determined. Based on the data, the following variables were evaluated for ryegrass and wheat: crop growth rate (TCC = MSA/Ndays), with MSA being shoot dry mass and Ndays the number of days between emergence and plant harvesting; specific leaf area (SLA = Af /MSf),with Af being the leaf area and MSf leaf dry mass; and leaf area index (IAF = Af/St), St being soil area, indicating leaf area per soil area. Plant height, dry mass and leaf area of the susceptible ryegrass showed smaller reductions and better phenotypic plasticity, in function of the increasing density per soil area, compared to the resistant one. The susceptible biotype showed to be more competitive and its interference in wheat development was more visible at lower densities. It was concluded that the susceptible ryegrass biotype is more competitive than the resistant one.

Detecção da resistência de capim-arroz (Echinochloa sp.) ao herbicida quinclorac em regiões orizícolas do sul do Brasil

The monitoring of Echinochloa sp. plants resistant to quinclorac was conducted in Rio Grande do Sul and Santa Catarina, Brazil to determine the origin of resistance and its dissemination, as well as to detect practices or climatic conditions related to the selection and geographic distribution of the resistant biotype. The seeds were collected, purified and standardized, and trials conducted under growth chamber and greenhouse conditions. In the growth chamber, a standard germination test was conducted with the seeds being submitted to rates of 0x, 1x, 2x, 6x, 16x and 32x and to the recommended rate of quinclorac, followed by germination curve and seedlings survival evaluation 14 days after sowing (DAS); the same herbicide rates were evaluated under greenhouse conditions, applied over the plants 20 days after emergence (DAE). Dry weight and control were evaluated 35 DAE, and biotypes with RI above four were considered resistant. A map of both states was elaborated where distribution of resistance to quinclorac was showed graphically, followed by herbicide profoxydim test as an alternative for the resistant biotype control.

Densidades de plantas daninhas e épocas de controle sobre os componentes de produção da soja

This work aimed to evaluate the effects of different weed densities on the yield components of soybean grain, cv. BRS 243 RR. The experimental design was arranged in completely randomized blocks, and the treatments consisted of increasing periods of control and three weed densities (low, medium and high). The initial periods of control were: 0, 0-5, 0-10, 0-15, 0-21, 0-28, 0-35, 0-42, 0-49 and 0-125 (harvesting). In low infestation areas, the weed community was composed mainly of Brachiaria plantaginea, Ipomoea nil, Euphorbia heterophylla and others. In medium and high infestation areas, the outstanding weeds were Brachiaria plantaginea, Ipomoea nil, Digitaria horizontalis, Cyperus rotundus and others. B. plantaginea was responsible for the highest dry matter accumulation in all levels of infestation. Regarding the crop yield components, number of pods per plant was the most severely affected by competition, reduced at about 58% in the low infestation area, 71% in the medium infestation area and 78% in the high infestation area. Number of seeds per pod and weight of 1000 grains were less influenced by competition; however, these parameters were reduced, indicating a relation between weed control periods and infestation level with soybean yield component.

Período anterior à interferência na cultura da soja-RR em condições de baixa, média e alta infestação

The aim of this study was to evaluate the period before weed interference in soybean culture, cv. BRS 243-RR, under low, medium and high weed density. The experimental design was arranged in complete randomized blocks, and the treatments consisted of increasing periods of weed control (0, 0-5, 0-10, 0-15, 0-21, 0-28, 0-35, 0-42, 0-49 and 0-125 days). In low weed infestation area the main weed species were: Brachiaria plantaginea,Ipomoea nil,Euphorbia heterophylla. In medium and high infestation areas, Brachiaria plantaginea,Ipomoea nil,Digitaria horizontalis and Cyperus rotundus were the most frequent weeds. Considering 5% and 10% of tolerance of soybean grain yield reduction, it was concluded that the period before interference was 17 and 24 days after emergence (DAE) in low infestation, area 11 and 15 DAE in medium infestation area and 11 and 16 DAE in high infestation area. Weed interference during the full crop cycle reduced soybean grain yield in 73%, 82% and 92%, for low, medium and high weed density, respectively.

Glyphosate translocation in hairy fleabane (Conyza bonariensis) biotypes

The objective of this work was to evaluate the translocation of glyphosate in C. bonariensis plants resistant and susceptible to that herbicide. The 14C-glyphosate was mixed with commercial gyhphosate (800 g ha-1) and applied on the center of the adaxial face of a third node leaf, using a micro syringe, and adding 10 µL of a solution with specific activity of 1,400 Bq, 45 days after plant emergence. The concentration of the glyphosate translocated in the plant was evaluated at time intervals of 6, 12, 36 and 72 hours after being applied on the application leaf, stem, roots and leaves. Ten hours after treatment application, the distribution of the product in the application leaf, divided into base, center and apex, was also evaluated by measuring the radiation emitted by 14C-glyphosate in a liquid scintillation spectrometer. Greater glyphosate retention was observed in the resistant biotype leaf, approximately 90% of the total absorbed up to 72 hours. In the susceptible biotype, this value was close to 70% in the same period. Susceptible biotype leaves, stem and roots showed greater concentration of glyphosate, indicating greater translocation efficiency in this biotype. In the resistant biotype, the herbicide accumulated in greater quantity at the apex and center of the application leaf, while in the susceptible biotype greater accumulation was observed at the base and center leaf. Thus, it can be stated that the resistance mechanism is related to the differential translocation of this herbicide in the biotypes.

Interferência de plantas daninhas em diferentes densidades no crescimento da soja

Este trabalho foi realizado com o objetivo de avaliar os efeitos de densidades de plantas daninhas (baixa, media e alta infestacao) sobre as variaveis de crescimento da soja, cv. BRS 243RR. O delineamento experimental foi de blocos ao acaso, sendo os tratamentos constituidos por dez periodos de convivencia das plantas daninhas com a cultura (0, 0-5, 0-10, 0-15, 0-21, 0-28, 0-35, 0-42, 0-49 e 0-125 dias). As variaveis estudadas foram altura de plantas, massa seca dos ramos desprovidos de folha, massa seca das folhas, numero de folhas e area foliar da soja. As avaliacoes foram determinadas no final do periodo de interferencia, juntamente com a avaliacao de densidade e acumulo de fitomassa da comunidade infestante. Na area onde a soja foi cultivada sob baixa infestacao de plantas daninhas, observou-se aumento da densidade das infestantes em funcao do tempo apos a emergencia da soja. Todavia, o contrario foi observado nas areas de media e alta infestacao; nelas verificou-se reducao da densidade das plantas daninhas ao longo do periodo de avaliacao. A altura e area foliar das plantas de soja foram influenciadas pelo nivel de infestacao, o que nao foi observado para massa seca e numero de folhas. Conclui-se que o nivel de infestacao afeta de maneira diferenciada as variaveis que definem o crescimento da soja.

Controle de Capim-Arroz (Echinochloa spp.) em função de métodos de manejo na cultura do arroz irrigado

RESUMO - Objetivou-se com este trabalho avaliar a eficacia do herbicida penoxsulam emfuncao do inicio da irrigacao permanente e da epoca de sua aplicacao e dose no controle decapim-arroz ( Echinochloa crusgalli e E. colona), bem como sua seletividade a cultura do arrozirrigado, cultivar Qualimax-1. O experimento foi conduzido a campo em delineamentoexperimental de blocos ao acaso com quatro repeticoes, no esquema fatorial 2 x 3 x 4,representando epocas de inicio da irrigacao por inundacao (21 e 30 dias apos a emergencia– DAE), epocas de aplicacao (pre-emergencia e pos-emergencia inicial e tardia) e doses doherbicida penoxsulam (0, 18, 36 e 72 g ha

Weed management in raw sugarcane

In the last years, the sugarcane harvesting process has undergone changes imposed by law, environmental awareness or social pressure, leading to the exclusion of the traditional slash and burn before harvesting and inclusion of crude sugarcane harvest. This process is denominated crude harvesting. The adoption of this new harvesting system promoted alterations in the entire sugarcane tillage system, including wider row spacing and the formation of a mulching layer due to the deposition of sugarcane residues on the soil surface. This new crop management system affects directly the weed dynamics in these areas and soil fertility as well. Weed shifting has been observed, producing weed species with higher germination and emergence capacity under a thicker straw layer, compared to those unable to germinate due to the physical or allellopathic action of the straw. In addition, pre-emergence herbicides are usually less efficient under this system due to their retention in the straw, not reaching the soil in sufficient concentrations to promote weed control. In this literature review, the major results involving weed management in crude sugarcane areas are described to provide information to researchers, extension workers, and farmers on how to improve sugarcane integrated weed management, mainly under this new harvesting process. The results show that reduction of herbicide dependence is feasible, leading to improved soil quality in these fields.

Aspectos da resistência de Sagittaria montevidensis ao herbicida pirazosulfuron-ethyl inibidor da ALS

The ALS-inhibiting herbicides are highly effective when applied in low rates, presenting low toxicity to mammalians, wide control spectrum and, some of them, long soil persistence. Usually, the resistance mechanism for ALS inhibitors is due to the lack of enzyme sensitivity to the herbicide, resulting from alterations in the enzyme conformation. However, crop tolerance mechanisms are observed, such as differences in absorption, translocation and degradation before the herbicide reaches the target site. The objective of this research was to evaluate aspects related to the level and main absorption mechanism of pyrazosulfuron-ethyl to determine the resistance mechanism of an ALS-resistant S. montevidensis ecotype. Experiments were carried out under growth chamber, and greenhouse conditions. The treatments were 20x; 22x; 24x; 26x and 28x (X=label rate) of pyrazosulfuron-ethyl (20 g a.i. ha-1), applied individually on the shoots, roots and seeds of a resistant and a susceptible ecotype. The results showed some differences between susceptible and resistant ecotypes in relation to the main site of herbicide absorption.

Water use efficiency in sugarcane genotypes submitted to herbicide application.

The objective of this study was to evaluate the effects of the herbicides ametryn and trifloxysulfuron-sodium, applied alone or in mixture, on the characteristics associated to water use efficiency in sugarcane varieties under field conditions. The trial was installed in a completely randomized block design with split-plots and four replications. Plots were composed by the herbicides ametryn, trifloxysulfuron-sodium or a commercial mixture of ametryn + trifloxysulfuron-sodium, applied 65 days after planting, plus a control mechanically free of weed infestation; split-plots were composed by sugarcane varieties (RB72454, RB835486, RB855113, RB867515, RB947520 and SP80-1816). Fifteen days after herbicide application, stomatal conductance (Gs), temperature gradient between leaf and air (DT) and transpiration rate (E) were evaluated, and water use efficiency (WUE) was obtained as a function of photosynthesis and transpiration rates. Plant shoots were also collected for dry matter determination. Variety RB855113 presented the greatest damage to water use efficiency and transpiration and was thus considered the most sensitive to ametryn and trifloxysulfuron, while varieties SP80-1816 and RB867515 were the most tolerant. In these varieties, herbicides caused only minor changes in water use efficiency and thermal gradient. Stomatal conductance, leaf temperature, transpiration and water use efficiency were effective in identifying herbicide damage to crops, mainly those caused by photosynthesis-inhibiting herbicides; sugarcane genotypes showed a different behavior in relation to herbicide susceptibility and varieties SP80-1816 and RB867515 were the less affected by the herbicide treatments; on the other hand, RB855113 was the most severely affected.