Cassava is a perennial shrub of the family Euphorbiaceae, cultivated mainly for its starchy roots. It is one of the most important food staples in the tropics, where it is the fourth most important source of energy. On a worldwide basis it is ranked as the sixth most important source of calories in the human diet (FAO, 1999). Given the crop’s tolerance to poor soil and harsh climatic conditions, it is generally cultivated by small farmers as a subsistence crop in a diverse range of agricultural and food systems. Although cassava is a perennial crop, the storage roots can be harvested from 6 to 24 months after planting (MAP), depending on cultivar and the growing conditions (El-Sharkawy, 1993). In the humid lowland tropics the roots can be harvested after 6–7 months. In regions with prolonged periods of drought or cold, the farmers usually harvest after 18–24 months (Cock, 1984). Moreover, the roots can be left in the ground without harvesting for a long period of time, making it a very useful crop as a security against famine (Cardoso and Souza, 1999). Cassava can be propagated from either stem cuttings or sexual seed, but the former is the commonest practice. Propagation from true seed occurs under natural conditions and is widely used in breeding programmes. Plants from true seed take longer to become established, and they are smaller and less vigorous than plants from cuttings. The seedlings are genetically segregated into different types due to their reproduction by cross-pollination. If propagated by cuttings under favourable conditions, sprouting and adventitious rooting occur after 1 week.

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Cassava botany and physiology.

A mandioca (Manihot esculenta) e cultivada em varios paises, sendo de grande importância como fonte de energia para alimentacao humana e animal e na geracao de empregos e renda. No Brasil, apesar de essa cultura apresentar alto potencial produtivo - em alguns estudos alcancando valores superiores a 100 t ha-1 de raizes - , a produtividade nacional e baixa, atribuida em grande parte ao manejo inadequado das plantas daninhas. A interferencia dessas plantas resulta em competicao pelos recursos essenciais, como nutrientes, agua e luz. Alem disso, o controle realizado de maneira incorreta das plantas daninhas nos mandiocais dificulta outros tratos culturais e aumenta os custos de producao. Nesta revisao sao abordados os aspectos relativos ao manejo das plantas daninhas na cultura, descrevendo, de forma detalhada, os principais componentes de interferencia. Discute-se, em varias situacoes, o periodo critico de competicao. Por fim, sao apresentados os principais metodos de controle visando a utilizacao do manejo integrado como forma sustentavel do controle de plantas daninhas nessa cultura.

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Manejo de plantas daninhas na cultura da mandioca

Two experiments were carried out to evaluate the effect of different periods of control or coexistence of Euphorbia heterophylla on soybean (cv BRS-133) grain yield at low seeding rate, at Boa Terra Farm, Quarto Centenario-PR, Brazil, during 1999-2000 growing season The treatments for both experiments consisted of keeping the crop either with or without E heterophylla for 5, 12, 19, 26, 33, 40, 47, 54, 61 and 68 days after emergence (DAE) and during the whole cycle At the first weeding, for those treatments kept for increasing periods with weeds, and at harvest, for those treatments kept for increasing periods free of weed competition, E heterophylla densities and biomass were recorded The presence of weeds caused a yield daily loss of 515 kg ha-1, whereas their absence provided a yield daily gain of 727 kg ha-1 Weed-crop coexistence for up to 17 DAE did not cause any negative effect on crop yield, and the maximum length of time in which weeds had to be controlled to prevent crop yield losses was 44 days after emergence The critical period of interference was, therefore, from 17 to 44 DAE

Critical period of interference of Euphorbia heterophylla in soybean crop under low seeding rate

The choice and correct use of nozzles are essential for the best agrochemical deposition, which is indispensable. The aim of this work was characterize the spray pattern and the droplet diameter offering information to optimize the nozzles spaces in spray boom. Deposition pattern of flat fan nozzles Teejet XR 110015 VS were evaluated, in a patternator, with the nozzle placed 0.50 m above patternator under pressures of 200 and 300 kPa, and the droplet diameter by the laser diffraction method. The maximum distance calculated for an acceptable coefficient of variation (C.V.) was of 0.85 m for the pressures of 200 and 300 kPa, with values of 9.52 and 9.58%, respectively. The optimum distance was around of 0.70 m and to C.V. around 5%. Comparing pressures, it had significant difference for DV0.1 and DV0.5 but not for DV0.9. However the increase on the pressure resulted in a reduction of droplet size there was no significant effect of span due the pressures evaluated. It was concluded that the maximum spacing between nozzles would not be over 0.85 m and the DV0.5 decreased with the increase of pressure from 200 to 300 kPa, but without significance changes of span to droplet sizes.

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Caracterização do perfil de deposição e do diâmetro de gotas e otimização do espaçamento entre bicos na barra de pulverização

A weed infestation survey was performed in 20 second corn crop areas in 1997 and in 40 areas in 1998 and 1999 after soybean planting in the Medio Paranapanema Region, Sao Paulo. The survey was conducted in the counties of Assis, Campos Novos, Cândido Mota, Cruzalia, Florinea, Maracai, Palmital, Pedrinhas Paulista and Platina. When the corn reached the grain filling stage, the crop weeds were evaluated by zigzag walking through the areas starting from different points to represent the whole area. The crops were classified in three types, according to the system applied: no-tillage, conventional system with disc plowing, and second corn crop in the soybean straw only. Infestation level and occurring weed species were evaluated in each crop. The weed control systems adopted were also considered, according to the herbicides applied. The most important weed species occurring in the areas were: Cenchrus echinatus, Bidens pilosa, Euphorbia heterophylla, Raphanus sativus, Digitaria horizontalis, Commelina benghalensis, Amaranthus sp., Achyrocline satureioides, Sinapis arvensis, Sida sp., Glycine max, Avena strigosa, Eleusina indica and Sorghum halepense. The results showed a strong infestation increase of C. echinatus, which turned out to be the most important weed species in the area evaluated. R. sativus was also important and showed an expressive increase from 1997 to 1999. Weed infestations were higher in the conventional system areas, showing that this system is inferior to the others, concerning weed control. The chemical weed control most used was the mixture of (atrazine+oil) plus 2,4-D, followed by (atrazine+oil) and atrazine alone. No weed control was used in 22% of the crops, which were the most infested. The infestation level varied from year to year for the different weed control systems, depending on climate conditions.

http://www.scielo.br/pdf/pd/v25n2/a07v25n2.pdf

Plantas infestantes em lavouras de milho safrinha, sob diferentes manejos, no Médio Paranapanema

O trabalho analisa as possibilidades das estimativas das areas (9) de foliolos do apice, meio e base de folhas de Cassia tora L., atraves das equacoes lineares (Y = A + BX ) e (Y = BX), geometricas ou potenciais (Y= A XB ) e exponenciais (Y = ABX ). O valor de X e tomado das medidas lineares do foliolo, a saber: comprimento da nervura principal (C) , largura maxima perpendicular a nervura principal (L) ou o produto C.L. A analise de 360 foliolos mostra que as areas podem ser estimadas de maneira proporcional ao retângulo C x L. Os coeficientes de correcao foram 0,6711 para os foliolos do apice, 0,7404 para as medianas e 0,7759 para as da base. Houve diferencas estatisticamente significativas entre os coeficientes, nao sendo possivel estabelecer-se um unico coeficiente para os tres foliolos.

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Métodos para estimativa da area foliar de plantas daninhas: 4 , Cassia tora L.

The period for cassava planting is very wide in Sao Paulo State, Brazil, covering the whole dry season (May to October). There are large differences in the plant growth and its interference with the weed community when the planting time is early or late in the dry season. Aiming to study the weed interference on cassava growth and productivity, four field assays were carried out under different planting times (06/28/1989, 06/30/1989, 10/30/1989, and 07/23/1990) in a randomized complete blocks experimental design with three or four replications. The treatments were divided in two groups: in the first one (group 1), the crop was maintained weedy from the planting date to 30, 60, 90, 120, 150, 180, 210, 240, 270 and 360 days. In the second group (group 2), the crop was kept weed free from the planting date to 30, 60, 90, 120, 150, 180, 210, 240, 270, and 360 days. The weed interference reduced drastically the dry matter accumulation by the cassava plants and the root production losses reached up to 90%. The increase in the rate of dry matter accumulation in the cassava roots in the presence of weed could not be analyzed in two assays. In the group 2, all the data were properly analyzed in the four assays. The Boltzman Sigmoidal Equation suited well the data on cassava root dry matter accumulation and provides good prediction models. The best dry matter production was obtained for 360 day old roots.

Acúmulo de matéria seca na presença e na ausência de plantas infestantes no cultivar de mandioca srt 59 - branca de santa catarina

A avaliacao do desempenho de bicos de pulverizacao pode ser feita a partir do seu padrao de distribuicao do liquido. Pelo metodo descrito em Perecin et al. (1994), analisaram-se comparativamente os padroes de deposicao produzidos por bicos TF-VS4, TJ60-11006 e TQ15006 em mesa de prova, bem como as suas propriedades em barra total em termos dos coeficientes de variacao sistematico (CVS), aleatorio (CVA) e combinado (CVG), propondo-se uma formula para estimar o CVG da barra total. Os bicos TF-VS4 apresentaram CVG inferiores a 10%, mesmo com espacamentos entre bicos de ate 50 cm, e altura do alvo ao redor de 20 cm ou mais. Os bicos TQ15006 mostraram variabilidade acentuada na regiao central do padrao, o que proporcionou CVG em barra total superiores a 10%, com espacamentos entre bicos maiores que 25 cm. Os bicos TJ60-11006 comportaram-se de forma intermediaria entre os TF-VS4 e os TQ15006. A formula proposta para estimar o coeficiente de variacao combinado e: CVG=[(CVA) 2 + (CVS) 2 ] 1/2 .

Padrões de distribuição de líquidos obtidos com bicos TF-VS4, TJ60-11006 e TQ15006 em mesa de prova

O presente trabalho foi realizado em 1988, na Estacao Experimental de Agronomia da Alta Paulista, em Adamantina, na safra da seca, para estudar o efeito de diferentes periodos de competicao do mato no amendoim. Os tratamentos foram vinte, a saber: com e sem presenca do mato em todo o ciclo da cultura e, os resultantes da combinacao fatorial entre a presenca e a ausencia de mato no inicio da cultura e as epocas de remocao da flora infestante - 20, 30, 40, 50, 60, 70, 80, 90 e 100 dias apos a semeadura. Cada parcela foi constituida de quatro linhas, com bordadura comum entre as unidades experimentais, perfazendo, com a area util, 6,0 m2. As especies da flora infestante que ocorreram com maior frequencia foram Cyperus lanceolatus Poir., Digitaria horizontallis Willd., Brachiaria decumbens Stapf. e Portulaca oleracea L. A convivencia do mato com o amendoim diminuiu a producao de vagens e de graos e a biomassa seca da planta. Nao se observou efeito do mato sobre o indice de colheita e o rendimento de graos em nenhum dos periodos estudados. Uma capina aplicada oito dias ou aos 73 dias apos a semeadura, respectivamente, para os tratamentos sem e com mato no inicio, foi suficiente para a producao de vagens de amendoim estatisticamente igual a obtida quando a cultura foi mantida sem competicao durante todo o ciclo.

Efeitos dos períodos de competição do mato na cultura do amendoim: i. safra da seca de 1988

Com o objetivo de estudar os efeitos de diferentes periodos de matocompeticao sobre o crescimento e produtividade da cultura do amendoim cultivar Tatu-53, conduziu -se o presente experimento sobre solo Latossol Vermelho escuro fase arenosa na regiao de Jaboticabal, SP Constituiram-se os tratamentos de varios periodos de convivencia da comunidade infestante na cultura do amendoim, considerados a partir da emergencia da cultura ate 14, 28, 42, 56, 70, 84 e 117 dias (colheita) Apos o periodo de convivencia, a cultura foi mantida no limpo atraves de capinas na entre-linha e monda na linha de semeadura, a cada duas semanas Houve ainda, um tratamento em que a cultura foi mantida no limpo durante todo o ciclo O espacamento foi de 0,60 m com densidade de 25 sementes por metro de sulco As principais especies de plantas daninhas que ocorreram na area experimental foram Cenchrus echinatus L, Digitaria sanguinalis (L) Scop, Alternantera ficoidea (L) R Br, Emilia sonchifolia DC e Sida spp O periodo em que a competicao torna-se critica para a produtividade do amendoim inicia-se entre 42 e 56 dias do ciclo da cultura Os parâmetros produtivos afetados pela matocompeticao foram producao de vagens e graos por hectare e por individuos, numero medio de vagens por planta e por parcela e distribuicao de graos de diferentes tamanhos na massa produzida

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Valdemir Antonio Peressin

Papers

Métodos para estimativa da area foliar de plantas daninhas: 4 , Cassia tora L.

Acúmulo de matéria seca na presença e na ausência de plantas infestantes no cultivar de mandioca srt 59 - branca de santa catarina

Padrões de distribuição de líquidos obtidos com bicos TF-VS4, TJ60-11006 e TQ15006 em mesa de prova

Efeitos dos períodos de competição do mato na cultura do amendoim: i. safra da seca de 1988

Efeitos de períodos de convivência das plantas daninhas sobre a produtividade da cultura do amendoim das secas