Herbicide selectivity in alfalfa crops

This study aimed to determine the selectivity of herbicides applied in pre- and post-emergence for alfalfa crops. Three separate experiments were carried out under greenhouse conditions. The first experiment was arranged in a completely randomized design with three replications in a 4 x 11 + 1 factorial scheme , with eleven herbicides (bentazon, chlorimuron-ethyl, fomesafen, fluazifop-p-butyl, saflufenacil, imazethapyr, clethodim, nicosulfuron, imazaquin, haloxyfop-methyl and MSMA), four doses of each herbicide (0.5 D, 0.75 D, 1.0 D and 1.25 D, where D = recommended dose), plus an untreated control. The products were applied to alfalfa plants at the stage of 4 to 5 leaf pairs. In the second experiment, the effect of pre-emergent herbicides on early alfalfa development was observed through a completely randomized design with five replications in a 3 x 4 x 2 factorial scheme, with three herbicides (hexazinone, atrazine + simazine, S-metolachlor), four doses (0.5 D, 0.75 D, 1.0 D and 1.25 D), and two types of soil texture (loamy and clay soil), plus an untreated control. The third experiment evaluated the action of atrazine, 2,550 g ha-1; clomazone - 600 g ha-1; diclosulam - 25 g ha-1; diuron+hexazinone - 936 + 264 g ha-1 and diuron+hexazinone +sulfometuron - 1,386 + 391 + 33.35 g ha-1 on alfalfa sown at different times after herbicide application. The effects of the treatments on alfalfa were evaluated according to visual phytotoxicity symptoms, plant height, and biomass of roots and shoots. Among the herbicides applied at post-emergence, imazethapyr, clethodim, haloxyfop-p-methyl and MSMA were selective for alfalfa, while among those applied at pre-emergence, none were selective, regardless of soil texture. The results of the third experiment showed that the herbicides diclosulam, hexazinone + diuron and atrazine caused less toxicity in alfalfa plants.

Selectivity of clomazone and S-metolachlor applied after cassava pruning

The objective of this work was to evaluate the selectivity of clomazone in two formulations and S-metolachlor applied on shoots of different sizes after pruning of 'Baianinha' cassava. The experiment was arranged in a randomized block design in a factorial 5 x 2 (5 treatments x 2 sizes of shoots after pruning - 10 and 33 cm) with four replications. The herbicides evaluated were: clomazone (encapsulated suspension - 900 g h-1), clomazone (encapsulated suspension - 1,080 g ha-1), clomazone (emulsifiable concentrate 900 g ha-1), S-metolachlor (1,920 g ha-1) and an untreated control. During the experiment, all plots were kept free of weed interference by hand weeding. It was concluded that both the formulations of clomazone and S-metolachlor were selective when applied on both the shoot sizes evaluated. However, the application of S-metolachlor on 33 cm shoots gave higher selectivity to 'Baianinha' cassava plants.

Effect of selectivity of herbicides and plant growth regulators used in sugarcane crops on immature stages of Trichogramma galloi (Hymenoptera: Trichogrammatidae)

Herbicides and plant growth regulators are often used in sugarcane management. However, the use of non-selective pesticides can cause adverse effects on the efficiency of beneficial insects in integrated pest management. Within this context, this study aimed to evaluate the effect of such products on the immature stages of the parasitoid Trichogramma galloi. Eggs of Diatraea saccharalis containing the parasitoid at the egg-larva stage and at the prepupal and pupal stages were immersed in test solutions of the following pesticides (maximum recommended doses for sugarcane): herbicides clomazone and diuron + hexazinone, and plant growth regulators trinexapac-ethyl and sulfometuron-methyl. The biological properties evaluated were emergence (F1 and F2) and number of eggs parasitized by T. galloi (F1). The products were classified according to percentage of reduction in emergence and parasitism: harmless (<30%), slightly harmful (30-79%), moderately harmful (80-99%) and harmful (>99%). The pesticides evaluated were considered to be harmless or slightly harmful to immature T. galloi and, thus, their use should be preferred for preserving this parasitoid species in sugarcane management programs.

Selectivity of chemical weed control systems in conventional cotton

Cotton is highly susceptible to the interference imposed by weed community, being therefore essential to adopt control measures ensuring the crop yield. Herbicides are the primary method of weed control in large-scale areas of production, and usually more than one herbicide application is necessary due to the extensive crop cycle. This study aimed to evaluate the selectivity of different chemical weed control systems for conventional cotton. The experiment took place in the field in a randomized block design, with twenty nine treatments and four replications in a split plot layout (adjacent double check). Results showed that triple mixtures in pre-emergence increased the chance of observing reductions in the cotton yield. To avoid reductions in crop yield, users should proceed to a maximum mixture of two herbicides in pre-emergence, followed by S-metolachlor over the top, followed by one post-emergence mixture application of pyrithiobac-sodium + trifloxysulfuron-sodium.

Trinexapac-Ethyl and Sulfometuron-Methyl Selectivity to Young Eucalyptus Plants

Trinexapac-ethyl and sulfometuron-methyl are the most widely used ripeners in sugarcane. The application is performed by airborne spraying. Thus, if weather conditions are unfavorable, spray drift to neighboring areas may occur. The objective of this study was to assess the selectivity of the plant growth regulators trinexapac-ethyl and sulfometuron-methyl, used as sugarcane ripeners, to eucalyptus (Eucalyptus urograndis) young plants. The experiment was installed in an eucalyptus commercial yield area, in the municipality of Tambaú, state of São Paulo, Brazil, and arranged in a 2 x 8 factorial design in randomized blocks with four replications. The treatments studied were trinexapac-ethyl and sulfometuron-methyl, sprayed in eight doses, 0; 1.0; 2.5; 5.0; 10; 25; 50 and 100% of the dose used in sugarcane as ripeners (200 g ha-1 of trinexapac-ethyl and 15 g ha-1 of sulfometuron-methyl). Chemical ripeners were applied on eucalyptus plants with 48 cm in height on average; 10.1 branches; 4.5 mm of stem diameter and 44.3 cm of crown diameter, at 46 days after seeding. Trinexapac-ethyl was selective to eucalyptus and stimulated crown diameter growth. At higher doses, sulfometuron-methyl promoted severe noticeable injuries in eucalyptus plants, such as apical bud death. However, during the assessment period the plants recovered and the visual symptoms of phytotoxicity and growth alterations were not observed at 60 days after application. The plant growth regulators trinexapac-ethyl and sulfometuron-methyl were selective to eucalyptus young plants.

Selectivity of Saflufenacil for Sweet Sorghum and Potential use of Na-Bentazon as a Safener

The objective of this study was to assess the selectivity herbicide saflufenacil for two sweet sorghum hybrids, when sprayed in preemergence and postemergence, besides the use of Na-bentazon as a 'safener' for saflufenacil. Three experiments were conducted, in pots, maintained in an ambient condition (second and third experiments) and in a greenhouse (first experiment). In each experiment a completely randomized distribution was used, with four replicates. In the first (2 x 6 factorial) two hybrids of sweet sorghum (CVSW 80007 and CVSW 80147) and six dosages (0; 35; 52.5; 70; 87.5 and 105 g ha-1) of saflufenacil were studied, applied in preemergence of the plants. In the second (2 x 5 factorial) the same hybrids of sweet sorghum sprayed in postemergence with saflufenacil (0; 35; 52.5; 70 and 87.5 g h-1) were assessed. In the third (4 x 5 factorial) the association of Na-bentazon (0; 240; 480 and 720 g ha-1) to saflufenacil (0.35; 52.5; 70 and 87.5 g ha-1) was studied, when sprayed in postemergence on the sweet sorghum plants (CVSW 80007). Hybrid CVSW 80147 was more tolerant to saflufenacil than hybrid CVSW 800007, in preemergence or postemergence applications. The variables that best assessed the sensibility of the sweet sorghum to saflufenacil were number of emerged plants, for preemergence applications, and dry matter of stem for postemergence. Na-bentazon showed promise for use as 'safener' in postemergence applications of saflufenacil in sweet sorghum for dosages up to 70 g ha-1.

SELECTIVITY OF FOMESAFEN TO COTTON

ABSTRACT The aim of this work was to evaluate the selectivity of fomesafen alone or in a tank mixture with other preemergent herbicides, with or without S-metolachlor application in early postemergence in cotton plant, cultivar DP 555 BG RR(r). The design utilized was a randomized complete block, organized in a split-plot arrangement, with four replications. For that, 24 herbicides were evaluated with fomesafen (0.45 and 0.625 kg ha-1), prometryn (1.25 kg ha-1), diuron (1.25 kg ha-1), trifluralin (1.8 kg ha-1), and S-metolachlor (0.77 kg ha-1), applied as preemergent, with or without S-metolachlor (0.77 kg ha-1) applied in early postemergence. The variables evaluated were: phytotoxicity, insertion height of the first reproductive branch, plant height, stand, number of reproductive branches per plant, number of bolls per plant, bolls weight, and productivity of cotton seed. Fomesafen alone or in a tank mixture with preemergent prometryn, diuron, trifluralin and S-metolachlor was selective to cotton plant. Preemergent fomesafen isolated application followed by the application of S-metolachlor in early postemergence was also selective. However, on average, preemergent tank mixtures applied in association with preemergent S-metolachlor early application was not selective to cotton crop.

SULFENTRAZONE SELECTIVITY AND EFFICIENCY IN CASSAVA CROPS IN SANDY AND CLAYEY SOILS

ABSTRACT Weeds have the potential to dramatically interfere in cassava cultivation, reducing its productive potential; however, there are few studies on the selective herbicides in this crop. Therefore, the objective was to evaluate in this work the selectivity and efficiency of sulfentrazone in cassava crops grown in sandy and clayey soils. Two experiments were carried out: The first one was carried out in sandy soil conditions in the conventional system; and the second one was carried out in clayey soil conditions in the no-tillage system. The experimental design was a randomized block with four replications. The treatments consisted in doses of 250, 500, 750 and 1,000 g ha-1 of sulfentrazone, and weeded and non-weeded controls. Sulfentrazone application in cassava crops has linearly reduced the production of roots in a proportion of 0.0153 and 0.0107 t ha-1 at each increment in grams of the active ingredient, respectively. It was concluded that sulfentrazone was not selective for cassava crops grown both in sandy and in clayey soil; however, it was highly effective in weed control in both soils.

Light and storage on the germination of spores of Dicksonia sellowiana (Presl.) Hook., Dicksoniaceae

Spores of Dicksonia sellowiana are positively photoblastic and reach the maximum percentage of germination at 23 ± 2°C in white light after seven days of imbibition. The pre-induction phase for spores induced by white or red light for 24 hours was 72 hours. Gametophytes grown in white light were plane and bidimensional, while those grown under red light were filamentous. The higher the number of hours of light applied per day during 10 days, the higher the percentage of germination. Germination was higher for long white light treatments applied on a daily basis. The effect of different light intensities on germination was also investigated here. The lower percentages of germination were observed for spores kept under 43% and 2% of full sunlight, while those kept under 26, 19 and 4% presented higher percentages. Spores presented circa 82% of germination after 731 days of storage under refrigeration at aproximately 10°C.

Respuestas morfológicas y anatómicas de Tessaria absinthioides (Hook. et Arn.) DC. a la salinidad

T. absinthioides, Inuleae, Compositae, is a weedy species that is spreading in the irrigation area of the Colorado River, Argentina. This species can be found in normal and saline soils. Morphological and anatomical variables were measured with two salts, sodium chloride and sodium sulfate, with three levels of osmotic potential -0.4, -0.8 and -1.5 MPa, in hydroponic culture, using Hoagland solution as the cultivation media. The total diameter of the roots of plants growing in Na2SO4 and NaCl increased when the osmotic potential was -0.4 MPa. In plants growing in NaCl this may have resulted from the increase in the size of the cortical cells and in plants growing in Na2SO4, the diameter increased may be due to an increase in the cambial activity. The number and length of shoot internodes decreased with increasing salinity, even though this was not statistically significant. In comparison to the control, the total diameter of the shoot increased at -0.4 MPa and decreased with the reduction of the osmotic potential. In comparison to the control, the length of the leaves decreased at -0.4 MPa and the leaves width increased at the same concentration. The palisade parenchyma appeared less developed in saline conditions. In comparison to the control, the number of hairs increased at -0.4 MPa. T. absinthioides acts as a semihalophytic species, according to the salt ranks it tolerates. The mechanisms of adaptation to saline conditions are succulence in root and stunted growth if the salt in the media is NaCl, and the production of haloxeromorphic characters if the salt in the media is Na2 SO4

Pollination ecology of Tabebuia aurea (Manso) Benth. & Hook. and T. ochracea (Cham.) Standl. (Bignoniaceae) in Central Brazil cerrado vegetation

The pollination ecology and breeding systems of Tabebuia aurea (Manso) Benth. & Hook., and T. ochracea (Cham.) Standl. were investigated in an area of cerrado vegetation in the Federal District of Brazil. These species occur sympatrically, flower massively and synchronously for a month, during the dry season (July to September). Both have diurnal anthesis, with similar floral structures, a yellow tubular corolla and produce nectar. Fourteen species of bees visited both Tabebuia species, but, only three Centris species and Bombus morio, were considered potential pollinators, because of their high frequency on the flowers and their efficiency in carrying pollen. Tests on the breeding systems of T. aurea and T. ochracea demonstrated that boths species are self-incompatible, with late-acting self-incompatibility. The proportion of fruit set from cross pollination (T. aurea 17.2% and T. ochracea 12.3%) in both species was low considering the great number of flowers displayed. This suggests a lack of maternal resources for fruit-set. The great amount of seeds per fruit (about 92 in T. aurea and 285 in T. ochracea) may represent an investment of maternal resources allocated on higher quality of fertilized ovules.

Biologia reprodutiva e polinização de duas espécies de Polystachya Hook. no Sudeste do Brasil: evidência de pseudocleistogamia em Polystachyeae (Orchidaceae)

A fenologia, a biologia floral e reprodutiva, e o sucesso reprodutivo de Polystachya estrellensis Rchb. f. e P. concreta (Jacq.) Garay & H.R. Sweet foram estudados em matas mesofíticas semidecíduas da Serra do Japi (Jundiaí, SP), e na planície litorânea de Picinguaba (Ubatuba, SP), respectivamente. Ambas as espécies florescem no verão. Elas são principalmente epífitas e produzem inflorescências terminais com até 150 flores não ressupinadas. As flores exalam odor cítrico suave, principalmente nas horas mais quentes do dia. Ambas as espécies foram polinizadas por pequenas abelhas nativas, solitárias e sociais, que coletam pseudopólen do labelo das flores. O polinário é depositado na face frontal da cabeça das abelhas, enquanto elas recolhem pseudopólen. Tanto P. estrellensis como P. concreta são autocompatíveis. A maioria das flores de P. estrellensis (96,7%) é cleistógama, enquanto P. concreta produz apenas flores casmógamas. As flores cleistógamas de P. estrellensis apresentam tamanho e número dos elementos florais igual ao das flores casmógamas, fenômeno conhecido como pseudocleistogamia. Todas as flores de P. concreta, assim como as flores casmógamas de P. estrellensis, necessitam de um polinizador para transferência de pólen. A taxa de frutificação de P. estrellensis em condições naturais é maior que em P. concreta, principalmente por causa do grande número de flores pseudocleistógamas produzidas. Em matas mesofíticas semidecíduas da Serra do Japi, onde a taxa de frutificação de várias espécies de orquídeas é baixa, principalmente devido à escassez de polinizadores, a estratégia apresentada por P. estrellensis é um fator que contribui para o sucesso reprodutivo da espécie, comparado com as Epidendroideae não autógamas que ocorrem na região.

GABA-induced inactivation of Cebus apella V2 neurons: effects on orientation tuning and direction selectivity

We investigated the GABA-induced inactivation of V2 neurons and terminals on the receptive field properties of this area in an anesthetized and paralyzedCebus apella monkey. Extracellular single-unit activity was recorded using tungsten microelectrodes in a monkey before and after pressure-injection of a 0.25 or 0.5 M GABA solution. The visual stimulus consisted of a bar moving in 8 possible directions. In total, 24 V2 neurons were studied before and after blocker injections in 4 experimental sessions following GABA injection into area V2. A group of 10 neurons were studied over a short period. An additional 6 neurons were investigated over a long period after the GABA injection. A third group of 8 neurons were studied over a very long period. Overall, these 24 neurons displayed an early (1-20 min) significant general decrease in excitability with concomitant changes in orientation or direction selectivity. GABA inactivation in area V2 produced robust inhibition in 80% and a significant change in directional selectivity in 60% of the neurons examined. These GABA projections are capable of modulating not only levels of spontaneous and driven activity of V2 neurons but also receptive field properties such as direction selectivity.

Estrutura florestal em projeto de assentamento, comunidade São Mateus, município de Placas, Pará, Brasil

Este estudo teve por objetivo avaliar o potencial e a estrutura florestal de uma Floresta Ombrófila Densa de terra firme, da Comunidade São Mateus, município de Placas, Pará. A avaliação foi realizada em dois tipos de ambiente, sendo, um, em Floresta Manejada (FM) e, outro, em Floresta Não Manejada (FNM). Foram alocadas 20 unidades amostrais, sendo nove em FM e 11 em FNM. Em cada unidade amostral, os indivíduos foram inventariados em três classes de tamanho (CT): CT1 - 10 cm < DAP < 30 cm (subparcelas de 50 m x 25 m); CT2 - 30 cm < DAP < 50 cm (50 m x 50 m); e CT3 - DAP > 50 cm (50 m x 200 m). As formas de utilização de todas as espécies arbóreas registradas foram verificadas por meio de entrevistas com assentados, no comércio, nas feiras livres e no mercado municipal de Santarém. Foram amostrados 472,6 árvores/ha na FM, distribuídas em 134 espécies e, na FNM, 508,0 árvores/ha, distribuídas em 146 espécies. As espécies de maior valor de importância nos dois tipos florestais foram: Licania kunthianamm Hook. f. (Chrysobalanaceae) e Mezilaurus itauba Taubert ex Mez (Lauraceae). As espécies que mais se destacaram com diferentes possibilidades de uso foram: Protium cf. heptaphyllum (Aubl.) Marchand (Burseraceae), Hymenaea courbaril L. (Fabaceae) e Caryocar villosum (Aubl.) Pers (Caryocaraceae). Após quatro anos de colheitas, não ocorreu diferenciação estrutural entre FM e FNM.

Estoque e frações de carbono orgânico e fertilidade de solo sob floresta, agricultura e pecuária

O entendimento dos fenômenos de trocas de carbono entre solo, água e atmosfera é fundamental para o manejo e a conservação de ecossistemas naturais e agrários. Os objetivos deste trabalho foram determinar os estoques de carbono orgânico, as suas frações e a fertilidade do solo sob os manejos florestal (mata remanescente), integrando agricultura e florestas (eucalipto e cutieira) e em monoculturas agrícola (sob pivô central) e pastoril (braquiária), na Bacia do Rio Paraopeba, em Florestal-MG, visando a propor indicadores para a avaliação de manejo e conservação do solo. As amostras de solo foram coletadas em remanescente de mata nativa (Mata), em área agrícola cultivada sob irrigação de pivô central (Pivô) e em áreas de cultivo de Corymbia citriodora (Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson) (Eucalipto), Joannesia princeps Vell. (Cutieira) e Brachiaria decumbens Stapf (Pasto), nas profundidades de 0 a 20 e 20 a 40 cm. Os resultados indicaram que as estimativas dos estoques e de estabilidade do carbono orgânico aumentaram com a fertilidade do solo. Os sistemas florestais, principalmente a Mata, acompanhada pelos sistemas de manejo do solo integrando florestas à pastagem, em comparação com o cultivo contínuo ou a monocultura de pastagem, apresentaram estoques de carbono maiores, mais estáveis e menos solúveis, com formas mais aromáticas e hidrofóbicas (maior relação AH/AF), indicando menor potencial de lixiviação de carbono para o sistema aquático adjacente.