Alexandre Ferreira da Silva

Alterações nas características fisiológicas de cultivares de cana-de-açúcar submetida à aplicação de herbicidas

This work aimed to evaluate the influence of herbicides on the physiological characteristics of three sugarcane cultivars. The experiment was conducted in a randomized block design with three replications in a factorial design 3 x 8. Factor A was constituted of three sugarcane cultivars (RB867515, RB855156, and SP80-1816), and factor B of the herbicides tembotrione, MSMA, diuron + hexazinone, sulfentrazone, trifloxysulfuron-sodium, tebuthiuron, clomazone, and a treatment without herbicide (control). The transpiration rate of cultivar RB867515 plants was negatively affected when sulfentrazone, clomazone, and tebuthiuron were applied,compared to the control. Regarding water use efficiency, no differences were observed between the cultivars and the herbicides. Stomatal conductance of cultivars RB867515 and SP80-1816 was not affected by the herbicides. Only cultivar RB867515 presented lower photosynthetic rate when sulfentrazone was applied. The herbicides tested had distinct effects on the physiological characteristics of the three cultivars evaluated. Cultivar RB867515 showed the least variation in photosynthetic rate in the presence of the products tested, as compared to the control.

Selectivity of pre-emergence herbicides to physic nut (Jatropha curcas)

In recent years, the areas cultivated with physic nut (Jatropha curcas) have expanded in Brazil, aiming at its use in biofuel production. However, one of the problems faced by the producers is the lack of studies on its tolerance to the herbicides registered in Brazil. The objective of this work was to evaluate the tolerance of physic nut genotypes to herbicides applied at pre-emergence. The experiment was arranged in a randomized block design, with four replications, in a factorial design, 3 x 6. Factor A was composed by the genotypes (Filomena, Goncalo and Paraguacu), and factor B by the herbicides (isoxaflutole, oxyfluorfen, sulfentrazone, pendimethalin and tebuthiuron), plus one non-treated control. Intoxication by the herbicides was evaluated at 19, 32, 40, 48, 56 and 64 days after treatments (DAT). Height, leaf area, and plant dry matter were evaluated at 64 DAT. It was verified that the jatropha genotypes have different tolerance to the herbicides studied. Isoxaflutole and tebuthiuron caused severe injuries to all genotypes and negatively affected all the variables evaluated. On the other hand, oxyfluorfen and pendimethalin proved to be selective to the crop and should be evaluated in further studies to be recommended to the crop.

Photosynthetic activity of cassava plants under weed competition

The objective of this work was to evaluate characteristics associated with the photosynthetic activity of cassava plants under weed competition. The trial was carried out under field conditions, and experimental units consisted of 150 dm3 fiberglass boxes containing red yellow Latosol, previously corrected and fertilized. Treatments consisted in the cultivation of cassava plants which were free of weed competition and associated with three weed species: Bidens pilosa, Commelina benghalensis or Brachiaria plantaginea. After manioc sprouting started, 15 days after being planted, weeds that had been sown when manioc was planted were thinned, there were then eight plants left per experimental unit in accordance with specified treatments: cassava free of competition, cassava competing with B. pilosa, cassava competing with C. benghalensis and cassava competing with B. plantaginea. Sixty days after crop emergence leaf internal CO2 concentration (Ci), leaf temperature at the time of evaluation (Tleaf) and photosynthetic rate (A) were evaluated, also the CO2 consumption rate (ΔC) of cassava plants was calculated. A correlation matrix between variables was also obtained. All characteristics associated with photosynthesis in cassava plants were influenced by weed species. Cassava was more affected by B. pilosa and B. plantaginea in which concerns its exposition to solar radiation and water, while C. benghalensis seems to mostly affect the composition of incident light on the culture, allowing cassava to anticipate imposition when competing, even before it reaches harmful levels.

Glyphosate translocation in herbicide tolerant plants

The objective of this study was to evaluate glyphosate translocation in glyphosate-tolerant weed species (I. nil, T. procumbens and S. latifolia) compared to glyphosate-susceptible species (B. pilosa). The evaluations of 14C-glyphosate absorption and translocation were performed at 6, 12, 36 and 72 hours after treatment (HAT) in I. nil and B. pilosa, and only at 72 HAT in the species T. procumbens and S. latifolia. The plants were collected and fractionated into application leaf, other leaves, stems, and roots. In S. latifolia, approximately 88% of the glyphosate remained in the application leaf and a small amount was translocated to roots at 72 HAT. However, 75% of the herbicide applied on T. procumbens remained in the leaf that had received the treatment, with greater glyphosate translocation to the floral bud. It was concluded that the smaller amount of glyphosate observed in S. latifolia and T. procumbens may partly account for their higher tolerance to glyphosate. However, I. nil tolerance to glyphosate may be associated with other factors such as metabolization, root exudation or compartmentalization, because a large amount of the herbicide reached the roots of this species.

Water use efficiency of cassava plants under competition conditions

Objetivou-se com este trabalho avaliar caracteristicas associadas a eficiencia de uso da agua de plantas de mandioca sob competicao ou nao com plantas daninhas. O experimento foi realizado em condicoes de ambiente aberto, sendo as unidades experimentais compostas por vasos de fibra de vidro de 150 dm3preenchidos com Latossolo Vermelho Amarelo, previamente adubado. Os tratamentos consistiram no cultivo de plantas de mandioca isoladas e associadas a tres especies daninhas (Bidens pilosa, Commelina benghalensis e Brachiaria plantaginea). Apos inicio da brotacao das manivas, 15 dias apos o plantio, fez-se o desbaste das plantas daninhas, semeadas no momento do plantio das manivas, deixando-se oito plantas de B. pilosa, quatro de C. benghalensis e quatro de B. plantaginea. Aos 60 dias apos a emergencia (DAE), foram avaliados a condutância estomatica de vapores de agua (Gs), pressao de vapor na câmara subestomatica (Ean), gradiente entre temperatura da folha e do ar (ΔT), taxa de transpiracao (E) e a eficiencia do uso da agua (EUA). A especie B. pilosa demonstrou maior capacidade de afetar o crescimento das plantas de mandioca. B. plantaginea e muito eficiente em utilizar a agua, principalmente por apresentar metabolismo C4 , e se mantem competitiva com a mandioca mesmo sob baixo status hidrico temporario. C. benghalensis, por sua vez, nao e boa competidora por luz e aparentemente nao e causadora primaria do esgotamento da agua no solo. Os efeitos, nesse caso, das plantas daninhas, foram mais associados a competicao. No entanto, eles foram considerados entre moderados a baixos. Isso implica que a competicao estabelecida a nivel experimental foi baixa.

Interferência de plantas daninhas na cultura do sorgo sacarino

This work aimed to carry out a phytosociological study and to determine the critical period of weed interference on sweet sorghum crop. The experimental design adopted was randomized blocks with three replications. Treatments consisted by increasing periods of control or coexistence of weeds in different phenological stages of crop growth: 0-3 (V3), 0-5 (V5), 0-7 (V7), 0-9 (V9), 0-11(V11) fully expanded leaves and 0-R5 (harvest). The weed community was evaluated based on number the number of individuals and their correspondent dry mass accumulation, for each weed population in different periods of coexistence. Sweet sorghum was harvested at 101 days after emergence, when was measured plant height, culm diameter, total soluble solids (°Brix) in function of coexistence periods between crop and weeds, besides the yield of culms. Commelina benghalensis e Panicum maximum were the two species of higher relative importance at the crop harvested. The lack of weed control, during the crop cycle, caused an increase in total soluble solids (°Brix) and reduction of, respectively, 9 and 25% in plant height and culms diameter when compared with the hoed control during all cycle. Accepting losses of 5% in culm yield, was observed that the critical period of weed interference corresponded to the period of time between the phenological growth stage V3 to V11.

Efficiency of Brachiaria brizantha Control and Selectivity of the Herbicides {(Diuron+Hexazinone)+MSMA} Applied on Sugarcane

Chemical control is the main method used for weed management in sugarcane, with herbicides being usually applied in post-emergence. In some cases, serious toxicity is reported following herbicide application. To reduce the problem of injuries caused by herbicides to sugarcane, the doses used may be reduced to below those recommended in the label, with satisfactory control of the weed community still being obtained, when applied under appropriate environmental conditions. This study aimed to evaluate the efficiency and toxicity caused by doses ranging from zero to those recommended in the label of the herbicide mixture {(diuron + hexazinone) + MSMA} applied on the sugarcane variety RB867515, as well as on the weed species Brachiaria brizantha. The experiment was arranged in a completely randomized block design, with four replications. Treatments were allocated in a factorial design (6 x 3), with factor A being the herbicide (0.0, 50.0, 62.5, 75.0, 87.5 and 100.0% of the commercial dose): diuron + hexazinone (1,20 kg ha-1) and MSMA (1,44 kg ha-1), applied in combination; and factor B, the times of application ofthese herbicides, as follows: two to three leaves; four to five leaves and six to seven fully-expanded leaves, corresponding to the two- to four- leaf stages , 6 leaves to one tiller and one to four tillers of the weed species, respectively. At 7, 21, 35, and 49 days after herbicide application, visual analyses of intoxication and control of B. brizantha were carried out, as well as crop yield estimation, 12 months after planting. Considering the situations evaluated, the control of B. brizantha ranged between 50 and 100%, with higher control levels at the higher herbicide doses. The best control of B. brizantha throughout the crop cycle was found to occur when treatments were applied at the two- to- four-leaf stage of the weed species. Toxicity to the crop increased as the doses of {(diuron + hexazinone) + MSMA} increased in all evaluation times, with higher toxicity being observed when the herbicide mixture was applied at the most active growth stages of the crop, leading to lower crop yields.

Volunteer RR® corn management in roundup ready® soybean-corn succession system

The present study evaluated the effects of cover crops (Pennisetum glaucum, Crotalaria spectabilis and Urochloa ruziziensis) associated with the application of herbicides {glyphosate; (glyphosate + haloxyfop-R); (glyphosate + fluazifop-p-butyl); (glyphosate + imazethapyr) and (glyphosate + imazaquin)} in soybean desiccation management for volunteer RR® corn control. The experiment was conducted under field conditions at Sinop-MT, during the 2013/2014 crop season, in a randomized complete blocks design with factorial scheme and four replications. The following parameter were evaluated: dry matter of cover crops and ground coverage rate, control of volunteer RR® corn present at the time of desiccation, dry matter, height and intoxication level on soybean plants caused by herbicides at 7, 14 and 28 days after emergence (DAE), control of volunteer RR® corn derived from emergence fluxes subsequent to desiccation management and soybean yield. The joint application of (glyphosate + haloxyfop-R) provided the best level of volunteer RR® corn control present at the time of desiccation. Satisfactory control (80%) of volunteer corn was obtained with the application of (glyphosate + imazethapyr). This treatment displayed an additional residual effect of imazethapyr, which efficiently controled volunteer RR® corn derived from fluxes subsequent to desiccation management, especially in treatments performed under U. ruziziensis straw. None of the herbicides used in desiccation management caused any significant effect on dry matter, height and phytotoxicity of soybean plants at 7, 14 and 28 DAE nor on grain yield.

Características micromorfológicas de biótipos de capim‑arroz resistente e suscetível ao quinclorac

The objective of this work was to evaluate the effect of quinclorac on anatomical traits of leaves and roots of barnyardgrass (Echinochloa spp.) biotypes, susceptible and resistant to this herbicide, by micromorphometric assessments. Plants were grown in plastic pots with 250 cm 3 capacity. The images of plant sections were obtained with a light microscope equipped with a U-Photo system, coupled to a digital photo camera connected to a microcomputer. For cross-sections of leaf blades and roots, 10X objectives were used, and 20 sections/fields per plant were evaluated, with ten measurements per section and four replicates per treatment. Differences were observed between resistant and susceptible biotypes, both in the absence and in the presence of quinclorac. The resistant biotype shows leaf blades that are less affected by the herbicide; however, there are changes in root tissue constitution with increased aerenchyma formation. The susceptible biotype also shows formation of aerenchyma when treated with quinclorac, but in lower levels than those observed for the resistant biotype.

Interferência da Brachiaria brizantha nas características morfológicas da cana-de-açúcar

Weed interference is one of the main factors limiting sugarcane yield. Currently, there is little data on the density of weed species capable of causing economic damage to sugarcane. This work aimed to analyze the interference of Brachiaria brizantha in the morphological development of the sugarcane varieties RB72454, RB867515 and SP801816. The trial was installed under field conditions, with the treatments consisting of 12 densities of B. brizantha, as follows: 0, 1, 3, 7, 15, 32, 40, 32, 64, 92, 88 and 112; 0, 1, 4, 14, 10, 18, 28, 30, 36, 54, 52 and 72; 0, 1, 3, 6, 14, 20, 24, 26, 26, 32, 46 and 56 plants m-2 for the varieties RB72454; RB867515 and SP801816, respectively. One hundred and twenty days after emergence (DAE) of both the sugarcane plants and the weeds, shoot dry mass (SDM), leaf area (LA), diameter (D) and number of stems (NS), plant height (PH) and number of leaves of the crop were quantified. At harvest (350 DAE), crop yield (CY) was estimated. As B. brizantha density increased, lower values for leaf area, number of stems, dry mass and sugarcane yield were observed. On the other hand, as density increased, there was a correspondent increase in height and diameter of sugarcane stems. Variety RB72454 was the most affected by the iincrease of weed species density.