RESUMOO presente trabalho foi condu zido cor o obje tivo de avaliar os possíveis efeit os da inter ferên cia, part icularmen te a alelo pátic a, da palhada de Brach iari a decu mbens (BRA DC ) ABSTRACT Interference of Brachiaria grass mulch on initial growth of EucalyptusThe aim of this work was to evaluate possible effects of Brachiaria decumbens (BRADC) mulching resulted from either glyphosate application (1440 g.a.e./ha) or hand weeded on E. grandis initial growth. The plots were 50 l containers infested or not by BRADC. The experimental treatments consisted of no control of BRADC up to 230 days after Eucalyptus transplanting (DAT): BRADC control (using glyphosate or hand weeded at 106 DAT): simulation of treatment BRADC control not infested by BRADC, and BRADC mulch, resulted from glyphosate application or hand weeded, transfered from an area infested by BRADC. At the end of the experiment (230 DAT) it was observed a significant reduction on eucalyptus plant high, stem diameter, leaf and branch number, and leaf area, in the treatment where BRADC was not controlled, when compared to the plants growing in containers not infested by BRADC that received BRADC mulch obtained from glyphosate or manual hoeing. Chemical

Bromus catharticus Vahl. has been used as a valuable forage crop, but it has also been noted as a weed of winter crops and an invader in several countries. In Argentina, a putative glyphosate-resistant population of B. catharticus was identified as a consequence of the lack of effective control with glyphosate in the pre-sowing of wheat. Plant survival and shikimate accumulation analysis demonstrated a lower glyphosate-sensitivity of this population in comparison to a susceptible B. catharticus population. The resistant population was 4-fold more resistant to glyphosate than its susceptible counterpart. There was no evidence of target-site mechanisms of glyphosate resistance or an enhanced capacity to metabolize glyphosate in the resistant population. However, the resistant plants showed a lower foliar retention of glyphosate (138.34 μl solution g−1 dry weight vs. 390.79 μl solution g−1 dry weight), a reduced absorption of 14C-glyphosate (54.18 vs. 73.56%) and lower translocation of 14C-glyphosate from the labeled leaf (27.70 vs. 62.36%). As a result, susceptible plants accumulated a 4.1-fold higher concentration of 14C-glyphosate in the roots compared to resistant plants. The current work describes the first worldwide case of glyphosate resistance in B. catharticus. A reduced foliar retention of herbicide, a differential rate of glyphosate entry into leaves and an altered glyphosate translocation pattern would be the most likely mechanisms of glyphosate exclusion.

a b s t r a c tEleusine indica L. Gaertn. and Paspalum distichum L. are annual and perennial grasses, respectively that are widely distributed in turf and perennial cropping systems throughout Spain. Often, glyphosate is used between rows of perennial crops for control of these grasses, but variable responses have been observed. Sensitivity to glyphosate in each species was examined under greenhouse, laboratory and field conditions. In vitro tests on whole plants of both P. distichum and E. indica revealed no differences in sensitivity to glyphosate for areas with long-term use (treated; T) and no history of use (not treated; NT). The NT population of P. distichum (ED 50 73.1 g ae ha À1 ) was 11.6% more sensitive to glyphosate than NT E. indica (ED 50 81.6 g ae ha À1 ). No differences between T and NT populations of both species were observed for foliar retention of glyphosate as well as accumulation of shikimate. However, glyphosate retention and shikimate accumulation were up to 64 and 24.4% greater, respectively in P. distichum compared to E. indica. Within 96 h after treatment (HAT), foliar absorption of 14 C-glyphosate was similar among T and NT populations, but 8.8% higher for P. distichum compared to E. indica. Retention of 14 Cglyphosate in treated leaves of P. distichum was approximately 55% lower compared to E. indica. Translocation from the treated leaf into other shoot tissue (2.8-fold) and roots (8.5-fold) was higher for P. distichum versus E. indica. This would suggest that differences in E. indica versus P. distichum response to glyphosate are based upon differential retention in treated leaves and reduced movement out of treated tissue in other shoot and root tissue. In separate field experiments in citrus orchards, glyphosate and other herbicides were applied to assess control of E. indica and P. distichum over two years. Flazasulfuron and cycloxidim resulted in 90% or greater control of both species by 60 days after treatment (DAT). Only glufosinate, oxyfluorfen, paraquat and iodosulfuron resulted in >85% control of E. indica. These corresponding treatments ranged in effectiveness from 73 to 92% on P. distichum. Integration of effective herbicides with modes of action different than glyphosate should be used for management of E. indica and P. distichum and may delay the selection for resistance to glyphosate.

Experiments were carried out in controlled conditions to analyze the role of metabolism of glyphosate in Digitaria insularis (sourgrass) biotypes with differential response to the herbicide. Contents of glyphosate, aminomethylphosphonic acid (AMPA), glyoxylate, and sarcosine was detected in leaf tissues by using reversed-polarity capillarity electrophoresis. Glyphosate content in the A biotype increased from 19.7 up to 65.5 µg g fresh weight-1 , whereas decreasing from 19.9 down to 5.0 µg g fresh weight-1 in the B biotype, from 48 up to 168 hours after treatment. At 168 hours after treatment, percentage of the sum of AMPA, glyoxylate, and sarcosine was > 56% in the B biotype, whereas a small percentage of metabolites (< 10%) was found in the A biotype. Thus, the faster herbicide degradation in the B biotype is evidence that a differential metabolism of glyphosate can be conferring its lesser susceptibility to the herbicide.

Com o objetivo de obter uma equação que, através de parâmetros lineares dimensionais das folhas, permita a estimativa da área foliar de Brachiaria decumbens Stapf. e Brachiaria brizantha (Hochst.) Stapf., estudaram-se correlações entre a área foliar real (Sf) e parâmetros dimensionais do limbo foliar, como o comprimento ao longo da nervura principal (C) e a largura máxima (L), perpendicular à nervura principal. Todas as equações, exponenciais, geométricas ou lineares simples, permitiram boas estimativas da área foliar. Do ponto de vista prático, sugere-se optar pela equação linear simples envolvendo o produto C x L, considerando o coeficiente linear igual a zero. Desse modo, a estimativa da área foliar de B. decumbens pode ser feita pela fórmula Sf = 0,9810 x (C x L), ou seja, 98,10% do produto entre o comprimento ao longo da nervura principal e a largura máxima, enquanto que, para a B. brizantha a estimativa da área foliar pode ser feita pela fórmula SF = 0,7468 x (C x L), ou seja 74,68% do produto entre o comprimento ao longo da nervura principal e a largura máxima da folha.Palavras-chave: Fisiologia vegetal, gramíneas. ABSTRACT Leaf area estimative in weeds Brachiaria decumbens Stapf and Brachiaria brizantha (Hochst.) StapfIn order to obtain equations which make feasible the leaf area estiomate from linear measures of the leaf blade, correlation studies were done involving the real leaf blade area and main vein leaf lenght (C), maximum leaf width (L) and C*L. All the equations, linear, geometric and exponential, provide good leaf area estimate for both species. In the practical sense, it is suggested the use of the simple linear equation of the regression model using the C*L parameter and taking the linear coefficient equal zero. Then, the Brachiaria decumbens leaf area can be estimate using the equation Sf = 0,9810 (C*L) and the Brachiaria brizantha by using the equation Sf = 0,7468*(C*L).Key words: Weed physiology, grass weeds. INTRODUÇÃO Brachiaria decumbensStapf. e Brachiaria brizantha (Hochst.) Stapf. são espécies introduzidas da África do Sul como excelentes forrageiras perenes apresentando grande produção de massa foliar de boa qualidade e boa resistência ao pastoreio intensivo e ao pisoteio, especialmente em vastas regiões do Brasil Central.