Abstract Background Weeds compete with crops, demanding efficient control to avoid yield losses. Highly competitive cultivars are a cultural method that can increase weed suppression and reduce the effects of crop-weed competition. Objective The present study aimed to assess the competitive abilities of barley cultivars (crop) against black oat (weed) and their interference in crop physiology. Methods A preliminary additive experiment was carried out with increasing densities of barley and black oat to determine the minimal density from where there was no drier mass increasing per area. In the second experiment, a replacement series experiment, five plant proportions (100:0; 75:25; 50:50; 25:75, and 0:100) of the crop were used and the competitor was installed. Fifty days after the emergence, morphophysiological and physiological variables, as well as their respective relative competitiveness indexes, relative clustering coefficient, and species aggressiveness, were all assessed. Results The variables associated with the photosynthesis were dependent on the cultivar. BRS Cauê was the cultivar that performed better against black oat, with an increase in the overall photosynthetic rate, due to a smaller leaf area loss, as the competition increased. BRS Brau reduced the photosynthesis into smaller proportions for the competitor. The water use was not impacted to the same extent as photosynthesis. Conclusions BRS Cauê was the most competitive cultivar, suffering the lowest impact of competition with black oat.

A utilização do herbicida glyphosate para o controle químico das espécies de gramas-boiadeiras nas lavouras orizícolas não tem se mostrado eficiente. Nesse contexto, a investigação do controle dessas espécies com o glyphosate torna-se de fundamental importância, uma vez que não estão disponíveis no mercado herbicidas seletivos para o controle dessas em pós-emergência na cultura do arroz irrigado. Em vista do exposto, o objetivo do presente estudo foi avaliar a suscetibilidade das gramas-boiadeiras a diferentes formulações de glyphosate. Foram conduzidos dois experimentos em casa de vegetação em esquema fatorial. No primeiro experimento, o fator A constituiu-se de duas formulações de glyphosate (sal potássico e isopropilamina) e o fator B de nove doses dos herbicidas (zero; 175; 350; 700; 1400; 2800; 5600; 11200; 22400g e.a. ha-1). No segundo experimento, o fator A constituiu-se de duas espécies de gramas-boiadeiras (Leersia hexandra e Luziola peruviana), o fator B de três formulações do glyphosate (sal amônio, potássico e isopropilamina) e o fator C de nove doses dos herbicidas (zero; 87,5; 175; 350; 700; 1400; 2800; 5600; 11200g e.a. ha-1). Com base nos resultados obtidos, foi possível observar que as espécies apresentaram diferença de suscetibilidade ao herbicida glyphosate. Além disso, Leersia hexandra foi mais sensível em comparação a Luziola peruviana. As formulações de glyphosate influenciaram na suscetibilidade das espécies ao controle, sendo que, Roundup Transorb R® e Roundup Ultra® proporcionam melhor controle das espécies de gramas-boiadeiras.

The use of glyphosate to chemical control of Cutgrass and Peruvian Watergrass with the use of non-selective herbicides has not been efficient. In this context, the investigation of chemical control of these species to glyphosate is very important, since there are not available commercially selective herbicides to control these species in post-emergence of irrigated rice. Therefore, the objective of this study was to evaluate the susceptibility of Cutgrass and Peruvian Watergrass to different formulations of glyphosate. Two factorial experiments were conducted in a greenhouse, in the first the A factor were two formulations of glyhposate (potassium and isopropylamine salt) and the B factor were nine doses of the herbicide (zero; 175; 350; 700; 1400; 2800; 5600; 11200; 22400g a.e. ha-1). In the second experiment, the A factor were two species (Leersia hexandra and Luziola peruviana), the B factor were three formulations of glyphosate (amoniun, potassium e isopropylamine salt) and the C factor were nine doses of herbicides (zero; 87,5; 175; 350; 700; 1400; 2800; 5600; 11200g a.e. ha-1). Based on the results obtained, it was observed that these species exhibit differential susceptibility to glyphosate. Moreover, Leersia hexandra was more sensitive when compared to Luziola peruviana. Glyphosate formulation influenced control efficiency, where Transorb Roundup R® and Roundup Ultra® provided the best control of the two species.

A volatilização representa um processo importante no deslocamento de agrotóxicos para o ambiente. As características físico-químicas da molécula do clomazone indicam que este possui potencial de volatilização. Em vista do exposto, para a realização deste estudo, foram conduzidos dois experimentos com o objetivo de avaliar a suscetibilidade das espécies: pepino, melão, milho, sorgo e arroz a diferentes formulações do herbicida clomazone na fase vapor. Para isso, foram utilizadas caixas de vidro hermeticamente fechadas, com a presença de diferentes formulações de clomazone e as espécies vegetais. As formulações utilizadas foram Gamit 360 CS®, Gamit 500 EC® e Gamit Star®. Com os resultados obtidos, foi possível concluir que, dentre as espécies avaliadas, independente da formulação utilizada, a de menor tolerância ao herbicida clomazone na fase vapor foi o sorgo, seguido do milho e do arroz.

Volatilization represents an important transport process of pesticides for the environment. The clomazone physico-chemical properties indicate that molecule has the potential of volatilization. Therefore, for this study two experiments were carried with the objective of evaluating the species susceptibility: cucumber, melon, corn, sorghum and rice to different formulations of the herbicide clomazone in the vapor-phase. Glass boxes were used with the presence of clomazone formulations and plant species. The formulations used were Gamit 360 CS®, Gamit 500 EC® and Gamit Star®. As a main result it was conclude that among the species that were tested, independent of the formulation used, the lowest tolerance to clomazone herbicide in the vapor phase was sorghum, followed by corn and rice.

A temperatura do ar é um dos elementos meteorológicos mais importantes que afetam o desenvolvimento da planta de melancia. Para representar o efeito da temperatura do ar sobre o desenvolvimento das plantas, tem-se usado o método da soma térmica, por ser um método simples e por ser uma melhor medida de tempo biológico que dias do calendário civil ou dias após a semeadura. O objetivo deste trabalho foi determinar a soma térmica de três subperíodos de desenvolvimento da planta de melancia por diferentes métodos de cálculo. Um experimento em campo foi conduzido em Santa Maria, RS, com duas datas de semeadura durante o ano agrícola 2006-2007 (05/09/2006 e 21/09/2006). Usou-se a cultivar "Crimson Sweet" no delineamento experimental de blocos ao acaso com seis repetições. Os subperíodos foram semeadura-emergência (SE-EM), emergência-florescimento (EM-FL) e florescimento-colheita (FL-CO). A soma térmica diária (STd, °C dia) foi calculada por três métodos considerando-se as temperaturas cardinais de 10°C, 33°C e 42°C. A soma térmica acumulada (STa, °C dia) para os três subperíodos foi calculada somando-se os valores de STd. Não se constatou diferença na duração (STa) do ciclo total e dos subperíodos entre os três métodos de soma térmica utilizados. A duração (STa) do subperíodo EM-FL foi similar nas duas datas de semeadura (417°C dia), mas a STa dos subperíodos SE-EM e FL-CO variou de 98 a 130°C e de 770 a 840°C dia, respectivamente.

Air temperature is one of the most important environmental factors that drive development in watermelon. Thermal time is usually used for representing the effect of the air temperature on plant development because it is a simple method and a better time descriptor than calendar days or days after sowing. The objective of this study was to calculate the thermal time of three developmental phases in watermelon using different methods. A field experiment was carried out in Santa Maria, RS, Brazil, with two sowing dates during the 2006-2007 growing seasons (09/05/2006 and 09/21/2006). The cultivar 'Crimson Sweet' was used and the experimental design was a complete randomized block with six replications. Developmental phases were sowing-emergence (SO-EM), emergence-flowering (EM-FL) and flowering-harvest (FL-HA). Daily degree-days (DDD, °C day) were calculated with three methods using the cardinal temperatures of 10°C, 33°C and 42°C. Thermal time (TT, °C day) during the three developmental phases was calculated by accumulating DDD. There was no difference in the duration, in TT, for the total cycle and the developmental phases among the three methods of thermal time used. The duration (in TT) of the EM-FL phase was similar (417°C day) in the two sowing dates, but the TT of the SO-EM and FL-HA phases varied with sowing date from 98 to 130°C day and from 770 to 840°C day, respectively.