RESUMO -A tiririca (Cyperus rotundus) é uma espécie daninha de difícil manejo, causadora da redução do estande e do rendimento em plantios comerciais das mais variadas culturas. Devido à sua agressividade, capacidade de reprodução, alta dispersão e rusticidade, seu controle é difícil e oneroso. Objetivou-se com este trabalho avaliar métodos alternativos de controle da tiririca baseados na alelopatia e na homeopatia. No manejo com alelopatia, testaram-se extratos aquosos de feijão-de-porco (Canavalia ensiformes), mucuna-preta (Stizolobium aterrimum), alecrim-pimenta (Lippia sidoides) e capim-limão (Cymbopogon citratus). Com a homeopatia foi utilizada a escala centesimal hahnemanniana, onde se testaram as dinamizações 3CH, 6CH, 9CH e 12CH. Ambos os experimentos foram conduzidos em caixas gerbox transparentes, contendo areia grossa lavada, grãos de 1 a 3 mm de espessura, e 10 tubérculos sadios de tiririca, distribuídos uniformemente ao longo do recipiente. Após a aplicação dos tratamentos, os recipientes foram dispostos em estufa do tipo BOD a 25 o C, com fotoperíodo de 12 horas, onde permaneceram por 15 dias até a avaliação final. O extrato que apresentou o melhor manejo da tiririca foi o de alecrim-pimenta, que diminuiu o percentual de emergência e o vigor das plântulas; o extrato dessa espécie ocasionou maior efeito na redução do comprimento das plântulas de tiririca do que 2,5 kg ha -1 i.a. atrazina -herbicida utilizado para comparação. A homeopatia não apresentou diferença entre as dinamizações, não tendo assim efeito satisfatório no controle da tiririca. Os extratos de capim-limão, mucunapreta e feijão-de-porco não apresentaram efeitos alelopáticos. No entanto, o extrato de alecrim-pimenta é promissor no manejo alternativo de tiririca, sendo necessários novos estudos para elucidação dos princípios químicos envolvidos e da sua real ação no metabolismo da planta.Palavras-chave: alelopatia, extratos aquosos, controle alternativo.ABSTRACT -The nutsedge (Cyperus rotundus) is a harmful weed of difficult control, causing reduction of stand and yield of a wide variety of commercial crops. Due to its aggressiveness, reproduction capacity, high dispersion and rusticity, its control is difficult and costly. The aim of this work was to evaluate alternative methods of nutsedge control based on allelopathy and homeopathy. In the management with allelopathy, aqueous extracts of jack bean (Canavalia ensiformes), black velvet bean (Stizolobium aterrimum), rosemary pepper (Lippia sidoides) and lemon grass (Cymbopogon citratus) were tested. With homeopathy, the Hahnemannian centesimal scale was used, testing the 3CH, 6CH, 9CH and 12CH dynamizations. Both experiments were conducted in transparent Gerboxes containing washed coarse sand, 1 to 3 mm thick grains, and 10 healthy nutsedge tubers, distributed evenly within the container. After the application of the treatments, the containers were placed in a BOD germination chamber at 25 o C with a 12 hour photoperiod, where they remained for 15 days until the final evaluation. The ex...

The competition between weeds and crops is one of the main factors responsible for productivity losses in agricultural fields. This review aimed at presenting and discussing how the interactions between weeds and microorganisms can affect the competitive capacity of weeds and soil physicochemical properties. We also discuss how changes in the elemental stoichiometry of weeds can reflect their competitive and adaptative capacity. Although weeds are more dependent on associations with soil microorganisms than crops for growth, few studies have assessed the contribution of the soil microbiota to their competitive success in agroecosystems. When in competition, plants can change the elemental stoichiometry of their tissues in environments with varied nutrient availability. Elemental stoichiometry of plants has been particularly well studied using ecological approaches on the dynamics of weed populations in natural ecosystems, being a promising tool for understanding weed capacity to adapt to different agricultural managements. Plants control the biogeochemical cycles of carbon (C) and nitrogen (N) in the rhizosphere through a phenomenon known as the rhizosphere priming effect (RPE). Although this review has found some information in the literature that provides strong indications that the coexistence of weeds and crops may increase soil organic matter mineralization, we are not aware of studies investigating the effects of competition among these plants on RPE.

The 2-Chloroethylphosphonic acid (ethephon) and calcium carbide are used to induce and synchronize the flowering of pineapple crop. Some farmers have used the 2,4-D herbicide in combination with these flowering inducers. This practice is based on the hypothesis that 2,4-D would act as a growth regulator, increasing fruit size and weight. The objectives of this work was to verify if the use of 2,4-D, associated to calcium carbide or ethephon, influences the productivity and quality of the pineapple fruits and, also if the use of this herbicide leaves residues in the fruits. For this, two field experiments were carried out in two different farms. The treatments consisted of the application of ethephon and calcium carbide, alone, and in a mixture with two, four and six drops of 2,4-D in the center of the leaflet of the pineapple cv. “Pérola” at 10 months after planting. The use of 2,4-D mixed with calcium carbide or ethephon, regardless of the dose and culture environment, did not influence the size, weight, total soluble solids content, density and pH of the pineapple fruits. However, depending on the growing environment, ethephon + 2,4-D mixtures did not influence or reduce flowering and crop yield. No 2,4-D residues were found in the fruit pulp of pineapple. It was concluded that the use of 2,4-D as a growth regulator of pineapple under the conditions evaluated does not incorporate qualitative or quantitative benefits to the productive system of this crop. In addition, no 2,4-D residues were found in the fruit pulp of pineapple.

-Weed control is one of the most relevant costs of sugarcane production. If weeds are not controlled at the right time, the productivity and longevity of sugarcane plantations are reduced. In this crop, chemical control is the most used method, since it is efficient and it has a lower cost. Differentiated tolerance of sugarcane cultivars to the herbicide clomazone has been observed in the fields. However, there is no scientific evidence of this effect on the productivity of crops. This study evaluated the effects of clomazone on three sugarcane cultivars (RB966928, RB93579 and RB867515). Herbicide application was performed 40 days after the emergence of sugarcane plants and 7, 14, 21 and 28 days after the application, the toxicity caused by the herbicide in the culture was evaluated through grades ranging from 0 (no toxicity) to 100 (plant death). The harvest was performed 580 days after the herbicide application. On this occasion, the length and diameter of the stem, number of tillers, tons of stems per hectare, total soluble solids of the juice, sucrose of the juice, apparent purity of the juice, sugarcane fiber, reducing sugars and total recoverable sugars were evaluated. The differential tolerance among sugarcane cultivars in response to clomazone application in the early stages of crop development was confirmed. Nevertheless, in all cultivars, the symptoms of intoxication disappeared over time and did not reflect on crop productivity. It was concluded that plant control in the sugarcane crop with clomazone, following the recommendation of the manufacturer, does not interfere negatively in the growth, development and productivity of the crop.Keywords: selectivity, Saccharum spp., herbicide. RESUMO -As plantas daninhas, se não controladas no momento adequado, reduzem a produtividade e longevidade dos canaviais. Nesta cultura, o método químico de controle das plantas daninhas, por ser eficiente e de menor custo, é o mais utilizado. No campo, tem-se observado tolerância diferenciada de cultivares de cana-de-açúcar ao herbicida clomazone. Contudo, não existe comprovação científica desse efeito sobre a produtividade dos cultivares. Neste trabalho foram avaliados os efeitos do clomazone em três cultivares de cana-de-açúcar (RB966928, RB93579 e RB867515). A aplicação do herbicida foi feita aos 40 dias após emergência das plantas de cana, e aos 7, 14, 21 e 28 dias após a aplicação foram avaliadas as intoxicações causadas pelo herbicida na cultura, atribuindo-se notas que variaram de 0 (ausência de intoxicação) até 100 (morte das plantas