A.A. Silva

Manejo de plantas daninhas no consórcio de milho com capim-braquiária (Brachiaria decumbens)

The objective of this work was to evaluate the effects of nicosulfuron and atrazine mixture on weeds, corn and Brachiaria decumbens intercrops, cultivated under no-tillage and conventional tillage. Six nicosulfuron doses (0, 2, 4, 8, 16 and 24 g ha-1) in mixture with atrazine in the dose of 1.500 g ha-1 were evaluated, plus two controls, represented by both species in monocrop. Seminiferous propagation of the annual weeds was efficiently controlled by applying nicosulfuron in 8 g ha-1 in mixture with atrazine, regardless of the management systems. The perennial species (Artemisia verlotorum and Cyperus rotundus), of vegetative propagation, were not controlled by the herbicide mixture, regardless of the applied dose. Larger infestations of these species were observed under the conventional system. B. decumbens biomass was reduced in the intercrop with corn, when compared to its control in monocrop, presenting a greater reduction when submitted to the largest doses of nicosulfuron, in both planting systems. No difference was observed in the production of grains and corn straw, in function of the treatments studied, under both planting systems.

Avaliação de formulações de glyphosate sobre soja Roundup Ready

This study aimed to evaluate the effects of three glyphosate formulations (Roundup Ready® and R. Transorb® - both with isopropylamine salt and Zapp Qi®, formulated as potassium salt), on transgenic soybean. CD 219RR variety soybean plants displaying the CP4Epsps gene, tolerant to glyphosate, were cultivated. At 25 days after emergence (DAE), when plants showed the second trifolium completely expanded (stadiums V2-V3 ), formulations were applied at 2,000 g ha-1 . Plants intoxication was evaluated 15 days after application as well as the number and dry matter of leaflets, number of radicular nodules and foliar content of N, P, K, S, Ca, Mg, Fe, Cu, Zn, and Mn at flowering and grain yield at the end of the cycle. Soil basal respiration rate, microbial biomass carbon and metabolic quotient were evaluated through soil samples collected during soybean flowering. Isopropylamine salt, present in the Roundup Transorb formulation, was more harmful to the soybean plants, also providing a negative effect on the soil microbiota. Roundup Ready formulation, registered as transgenic soybean, should not be applied on this crop at a higher rate, since it could alter the content of some nutrients, such as N, Ca, Mg, Fe and Cu, besides causing intoxication in the plants.

Efeitos de diferentes formulações comerciais de glyphosate sobre estirpes de Bradyrhizobium

O objetivo deste trabalho foi avaliar efeitos de formulacoes comerciais de glyphosate sobre estirpes de Bradyrhizobium, em condicoes de laboratorio. As formulacoes foram aplicadas na concentracao de 43,2 µg L-1 do equivalente acido. As bacterias foram inoculadas em meio de cultura a base de manitol e extrato de levedura (YM). O efeito do herbicida no crescimento das estirpes de Bradyrhizobium foi avaliado mediante leitura da densidade otica em espectrofotometro. Avaliou-se o crescimento das estirpes de B. japonicum SEMIA 5079 e de B. elkanii SEMIA 5019 e SEMIA 587 sob efeito de nove formulacoes de glyphosate: Zapp Qiâ, Roundupâ, Roundup Multiacaoâ, Roundup Transorbâ, Roundup WGâ, Tropâ, Agrisatoâ, glyphosate tecnico [padrao de N-(phosphonomethyl) glycina] e controle sem adicao de herbicida (testemunha para as estirpes). Foram utilizadas seis repeticoes. Confeccionaram-se curvas de crescimento para cada estirpe. Pelos resultados, pode-se observar que todas as formulacoes de glyphosate causaram efeitos diferenciados sobre as estirpes de Bradyrhizobium SEMIA 5019, SEMIA 5079 e SEMIA 587. Constatou-se que a formulacao Zapp Qi foi a menos toxica as estirpes de Bradyrhizobium avaliadas. A maior toxicidade foi observada para Roundup Transorb, que provocou reducoes no crescimento acima de 94% para todas as estirpes de Bradyrhizobium estudadas. Nao se observou correlacao entre o tipo de sal - isopropilamina, amonio ou potassico, presentes na formulacao herbicida - e o grau de inibicao no crescimento das estirpes. SEMIA 587 foi a estirpe menos tolerante a maioria das formulacoes testadas, porem SEMIA 5019 foi a mais sensivel ao glyphosate padrao, sem adicao de sais ou de outros aditivos.

Sensibilidade de cultivares de cana-de-açúcar à mistura trifloxysulfuron-sodium + ametryn

The objective of this study was to evaluate the sensitivity of 11 cultivars (SP801842, SP79-1011, SP81-3250, SP80-1816, RB855113, RB835486, RB845210, RB867515, RB928064, RB72454 and RB855536) and four clones (RB947643, RB855002, RB957712 and RB957689) of sugarcane to the pre-formulated mixture of the herbicides trifloxysulfuron-sodium (18.5 g kg-1) + ametryn (731.5 g kg-1), termed Krismat®. Cultivars and clones were cultivated in vases under non-protected environment. In both assays, the herbicide mixture was applied at 60 days after sprouting. In assay 1, the herbicide mixture was applied at a single rate of 2.00 kg ha-1 on all the cultivars and clones, while in assay 2 it was applied at rates of 1.00; 2.00; and 6.00 kg ha-1 on cultivars RB855113 and RB867515. After herbicide application and harvest at 45 days after treatment (DAT), weekly evaluations of phytotoxicity (%),and dry matter were conducted as well. The variables plant height, leaf number, leaf area and dry matter of the aerial part and stalk were evaluated only in the second assay. RB855113 cultivar showed the highest sensitivity to the herbicide mixture; the genotypes SP80-1842, SP80-1816, SP79-1011 and RB957689 showed medium sensitivity and the clones presented good tolerance. For the RB855113 cultivar, the highest toxicity index was observed from 20 to 27 DAT. Reduction of plant height, leaf number, foliar area and dry matter of the aerial part and stalk was observed during this period due to the increase of the product doses. Cultivar RB867515 was tolerant at the lowest herbicide doses. However, it was found to be sensitive, at the highest tested dose.

Persistência de sulfentrazone em Argissolo Vermelho-Amarelo cultivado com cana-de-açúcar

The objective of this study was to evaluate sulfentrazone persistence in Typic Hapludalf and its effect on the microbiota of soil cultivated with sugar-cane. The treatments consisted of herbicide application only in 2003, in 2003 with reapplication in 2004 and control without herbicide. Herbicide distribution in the soil profile (0-10 and 10-20 cm of depth) and persistence in 467/24, 517/74, 550/107 and 640/197 days after application (DAA), were studied in the split-plots and split-split-plots, respectively. Indirect quantification of the residues was accomplished by bioassay and C-CO2 evolution together with microbial biomass (CBM) determination were evaluated in soil collected 640/197 DAA. Reduction of dry mass of the aerial part of Sorghum vulgare was verified during the entire evaluated period when the herbicide was applied in 2003 and reapplied in 2004. Most of the residues were detected at the depth of 010 cm, with their leaching potential in the soil being of little significance under environmental conditions. Sulfentrazone influenced the evolution of C-CO2 and CBM of the soil, with the largest accumulated value of C-CO2 being observed for the treatment without herbicide application. Sulfentrazone presented high persistence in PVA, with a negative effect on soil microorganisms, but without posing leaching risks in its profile.

Effects of weed species competition on the growth of young coffee plants

Este trabalho teve como objetivo avaliar os efeitos da competicao de sete especies de plantas daninhas sobre o crescimento de plantas de cafe, cultivadas em casa de vegetacao. Aos 30 dias apos o transplantio das mudas de cafe, em vasos contendo 12 L de substrato e com area de 6,5 dm2 na superficie do solo, fez-se o transplantio e/ou a semeadura das especies daninhas nesses vasos, em seis densidades (0, 1, 2, 3, 4 e 5 plantas por vaso). Os periodos de convivencia, desde o transplantio ou emergencia das plantas daninhas ate a colheita das plantas, quando do florescimento das plantas daninhas, foram de 77 dias - Bidens pilosa, 180 dias - Commelina diffusa, 82 dias - Leonurus sibiricus, 68 dias - Nicandra physaloides, 148 dias - Richardia brasiliensis e 133 dias - Sida rhombifolia. Foram avaliados a altura de plantas, o diâmetro do caule, o numero de folhas e a massa seca da parte aerea das plantas de cafe. Os efeitos da competicao de N. physaloides e S. rhombifolia sobre as plantas de cafe foram os menores comparados aos causados pelas demais especies de plantas daninhas, uma vez que apenas leves decrescimos - em todas as caracteristicas avaliadas - no cafeeiro foram observados. As demais especies de plantas daninhas causaram severa reducao no crescimento do cafeeiro, principalmente com o incremento da densidade delas. O grau de interferencia variou com a especie e com a densidade das plantas daninhas.

Fitorremediação do herbicida trifloxysulfuron sodium

This work aimed to evaluate the efficiency of plant species in the phytoremediation of the herbicide trifloxysulfuron sodium in soils, by using corn crop as a bioindicator. The treatments were composed by the combination of the species (Calopogonium muconoides, Crotalaria juncea, Crotalaria spectabilis, Vicia sativa, Cajanus cajan, Canavalia ensiformis, Helianthus annus, Dolichus lablab, Pennisetum glaucum, Stylosantes guianensis, Mucuna deeringiana, Mucuna cinereum, Mucuna aterrima, Raphanus sativus and Lupinus albus) sowed before the corn, without previous cultivation (control), and three rates of trifloxysulfuron sodium (0.00,3.75 and 15.00 g ha-1). The experiment was arranged in a randomized block design, in a factorial scheme, with three replicates. Eighty days after sowing, the plants were cut and the shoots discarded. After that, corn (cultivar AG-122) was sowed. Forty five days after emergence, corn height and shoot dry biomass were recorded. M. aterrima and C. ensiformis were considered efficient regarding decontamination of the herbicide residues in soil.

Dormência em sementes de plantas daninhas como mecanismo de sobrevivência: breve revisão

The high production of seeds in constantly disturbed environments is one of the main mechanisms of weeds survival. These seeds have usually some dormancy mechanism which constitutes weed species perpetuation in the crops. Seed dormancy can be characterized by temporally absence of the germination capacity, even though the seeds have satisfactorily conditions to germinate, thus allowing species survival under adversities, mainly those that make it difficult or hinder vegetative and reproductive growth. The causes of dormancy stem from two basic mechanisms: the first is related to inner seed events (embryo) and the second to outer characteristics in the seeds (tegument, endosperm or fruit barriers). Conceptually, dormancy can be classified as primary dormancy (when the mechanisms occur in plants-mother) and secondary dormancy (when the mechanisms causing dormancy occur after seed dispersion). These types of dormancy occur normally in weeds. Their alternation or cycling ensures germination flow these species, which depends on the characteristics occurring at the initial stages of seed formation (primary dormancy), and later, on the environmental conditions (secondary dormancy). However, many mechanisms coordinate dormancy, with the differences among them being still controversial. Thus, this study aimed to approach some of the main concepts and mechanisms in weed dormancy, in order to contribute and stimulate research which is still scarce in this area.

Atividade microbiana em solo cultivado com cana-de-açúcar após aplicação de herbicidas

The objective of this work was to evaluate the impact of the herbicides ametryn and trifloxysulfuron-sodium, singly or combined, and 2,4-D, on respiratory rate, microbial biomass, and metabolic quotient on sugar cane-cultivated soil. A completely randomized design was adopted in a split-plot scheme with four replications. The effect of the herbicides was evaluated in the plots and the effect of time after herbicide application in the split-plots. The herbicide doses, in kg ha-1, were: 1.30 (2,4-D), 1.00 (ametryn), 0.0225 (trifloxysulfuron-sodium), and 1.463 + 0.0375 for the mixture ametryn + trifloxysulfuron-sodium,, respectively. At 60 days after shoot emergence, the herbicides were sprayed on the sugarcane plants. At 15, 30, 45, and 60 days after herbicide application, rhizospheric and non-rhizospheric soil samples were collected and analyzed for respiratory rate (RR) microbial biomass (MB), metabolic quotient (qCO2), and total C-CO2 evolved from the soil (TCE). Ametryn applied singly or combined with trifloxysulfuron-sodium led to higher RR, while 2,4-D alone had little influence on this variable. Higher TCEs were verified in the soils of the treatments with trifloxysulfuron-sodium, ametryn, and with the compounds combined. Soil MB was reduced in the presence of ametryn applied singly or combined. These treatments resulted in higher values of qCO2 at 45 and 60 days of application, respectively.

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.