Glyphosate has been associated with control failures for Spermacoce verticillata in some Brazilian States. The objective of this work was to evaluate and determine the possible causes of this and propose alternative herbicides to use. Glyphosate was applied at three plant stages of development (2-4 leaves, 4-6 leaves and full bloom) where foliar absorption and translocation of glyphosate to various plants parts and time were analysed using the 14 C technique. Data were submitted to nonlinear regressions and analysis of variance, where means were compared by a Tukey test at 5% probability. Plant control by the application of different herbicides (19) in the same three stages of development of weed was evaluated. Twenty-one days after herbicide application, control was visually evaluated and data analysed and means were compared.Due to absorption and/or translocation problems, S. verticillata plants were not controlled by glyphosate. Plants with 4-6 leaves showed lower absorption and translocation of the herbicide to the leaf/root regions compared with plants at the beginning of their development. Plants at full bloom showed lower translocation of the herbicide to the root. In addition to the application of glyphosate at early stages of development, the application of paraquat, flumioxazin and mixtures of glyphosate with flumioxazin or cloransulam is recommended. Late applications could result in poor control, principally if glyphosate is used. Therefore, early applications are strongly recommended for control of this species.

Cyhalofop-butyl stands out among the herbicides in the control of imidazolinone-resistant Echinochloa species; but, rice farmers are not always satisfied with the control achieved with this herbicide. The objectives were to evaluate in regional scale the susceptibility of Echinochloa populations to cyhalofop-butyl, and quantify the effect of the weed phenology on its efficacy of control. For this, three trials were carried out under greenhouse conditions with a fully random design, using Echinochloa populations collected in rice fields in the southern region of Brazil. In two trials, the susceptibility level of 156 (2012/13 growth season) and 103 (2013/14 growth season) populations were evaluated with the application of cyhalofop-butyl at 360g ha-1. In other trial, in which treatments were arranged in a bi-factorial design (A = 6 x B = 5), it was evaluated six cyhalofop-butyl rates and five phenological stages of E. crus-galli populations. Echinochloa populations had showed differential susceptibility to cyhalofop-butyl, especially in the 2013/14 growth season, where 20 out of the 103 populations had control lower than 90%. The efficacy of this herbicide was inversely proportional to the phenological stage, and the application timing delay contributed directly to the decrease of susceptibility to the herbicide. Cyhalofop-butyl is an effective alternative to control imidazolinone-resistant Echinochloa populations, as long as the application timing occurs in the early phenological stages (2 to 4 leaves).

The sorghum crop in Brazil has expanded substantially. Among the factors that interfere in sorghum yield is the interference imposed by the presence of weeds. The objective of this study was to assess the potential of different herbicide treatments applied in pre-emergence or post-emergence of sorghum in terms of selectivity and weed control. Two experiments were conducted, one for each application modality: experiment 1: pre-emergence; experiment 2: post-emergence. The experimental design was a randomized block design with four replications, in split plots. For experiment 1, the pre-emergence herbicides applied constituted the plots, and the different sorghum hybrids (50A10, 50A40, 50A50, 1G100, 1G233, SS318) constituted the subplots. For experiment 2, the post-emergence herbicides applied constituted the plots, and the different sorghum hybrids (50A10, 50A40, 50A50, 1G100, 1G233, SS318) constituted the subplots. Based on the results obtained, and on the discussion done, it is possible to conclude that herbicides and their respectively doses that had potential for use in sorghum crop in pre-emergence were: atrazine (1000 and 2000), mesotrione (100), tembotrione (75), atrazine + mesotrione (1000+100 and 2000+100) and atrazine + trifluralin (1000+1000 and 2000+1000). Meanwhile in post-emergence the best options were: atrazine (1000 and 2000), mesotrione (50 and 100), bentazon (720), fluroxypyr (100), mesotrione + atrazine (50+1000) and mesotrione + fluroxypyr (50+100). All of those treatments provided less than 25% of plant injury which means less potential to reduce the sorghum grain yield.

This study aimed to analyze the in vitro growth and acclimatization of two cultivars (cv. 6323 and cv. 6546) of the species under different light quality regimes. To evaluate the influence of light quality on the growth of seedlings of the two cultivars, plants were submitted to five different light treatments: white, blue, yellow, green and red obtained by wrapping vials with colored cellophane sheets. After 60 days of cultivation, the multivariate statistical evaluation of the results was performed. From the biometric data analysis, it could be seen that the in vitro and ex vitro growth of P. amabilis were influenced by different light qualities and the resulting variation occurs due to the influence of the genotype. The blue spectrum exerted a greater influence on the cv. 6323 and the green spectrum on the cv. 6546.

Weed control is an essential practice in crop management. However, the use of herbicides may not be effective in certain situations, such as when problems are encountered in the application technology and when tolerant individuals and resistant biotypes are observed. In the cotton producing areas of the state of Bahia, Brazil, Spermacoce verticillata (shrubby false buttonweed) is not effectively controlled during burndown applications. During different developmental stages, plants can modify their leaves’ anatomical structures, which may influence herbicide control by modifying the retention, absorption, translocation and final effect of the chemical. This study assessed the morphological and histological differences in Spermacoce verticillata leaves at different stages of development. Leaves were collected from plants at different phenological stages (2-4 leaves, 4-6 leaves and flowering) and subjected to histological and scanning electron microscopy analyses. In the histological analysis, four leaves were collected from the upper nodes. The evaluated characteristics were the total leaf blade thickness, palisade and spongy parenchymal thicknesses, cuticle and epidermal cell thicknesses on the abaxial and adaxial surfaces and midrib height and width. Surface analyses were performed by observing the leaves under a scanning electron microscope. As the developmental stages of Spermacoce verticillata advanced, the plants began to show reduced leaf thickness due to the decreased abaxial epidermal thickness, transport vessel size and parenchymal thickness. At more advanced stages of development (4-6 leaves and flowering), the adaxial leaf surfaces showed fewer stomata and more trichomes.