Ricardo Trezzi Casa

Doenças do milho causadas por fungos do gênero Stenocarpella

Stemocarpella macrospora and S. maydis may cause seed rot, seedling blight, stem and ear rot and leaf spot in corn. Normally these fungi are the main grain rot causal agent when ears are infected. The damage caused exclusively by Stenocarpella has not yet been determined. The pathogens are found in practically all maize-growing regions of Brazil. The major disease intensity occurs under corn monoculture, mainly in small farms and fields for seed production where corn is continuously cultivated. Corn debris and infected seed are the primary source of inoculum. The inoculum, consisting of conidia produced in plant debris, is disseminated at short distance by wind and rain splash. Long distance dissemination occurs by seeds. Plant infection may occur systemically with inoculum coming from seeds, as mycelium, and/or through direct penetration of leaf sheats, foliar blade, peduncle and ear husks, from spore deposition, germination and penetration. The optimal temperature for mycelial growth and conidial germination is between 23 and 28 oC for both fungi. The main strategies to control these diseases are based on the elimination and/or reduction of primary inoculum, the use of healthy seed, seed treatment with fungicide of the benzimidazoles group and crop rotation. There is little information about disease resistance in commercial hybrids in Brazil. Balance of soil fertility and avoidance of high plant population may also help to reduce the infection.

Danos causados pela infecção de Gibberella zeae em trigo

Damages caused by infection of Gibberella zeae in wheat Fusarium head blight or wheat scab, caused by Gibberella zeae, is a disease of the floral infection, with frequent occurrence in regions where long periods of rain (> 48 h) and average temperatures (> 20 o C) occur after the wheat (Triticum aestivum) begins to flower. The reduction of grain yield, caused by nature infection of wheat scab in the field, has been quantified in different wheat cultivars during the harvests of 2001 and 2002, in the city of Passo Fundo, RS. All the wheat scab spikes, from the grain milk stage through maturation, had been identified and marked in an area of the 1 m 2 , being sampled three repetitions for wheat area. The scab and healthy spikes were harvested, dried, counted and threshed separately. The damages caused by wheat scab were calculated by the difference between the actual yield and the estimated yield potential based on the total numbers of spikes, the number of healthy spikes and the number of scab spikes. The average damage caused by wheat scab in 25 samples of wheat collected in 2001, was 13,4%, varying from 6,4 to 23,1%. In the 2002 harvest, the average damage in 18 samples, was 11,6%, varying from 3,1 to 20,5%. The average reduction in the grain yield for harvests of 2001 and 2002 were 394,4 Kg.ha -1 and 356,8 Kg.ha 1 , respectively. In the two harvests, the average damage caused by wheat scab, in the different cultivars, was 375,3 kg.ha -1 or 6,26 bags of wheat/ha.

Dispersão Vertical e Horizontal de Conídios de Stenocarpella macrospora e Stenocarpella maydis

Vertical and horizontal dispersion of conidia of Stenocarpella macrospora and Stenocarpella maydis Experiments were carried out in the field to quantify airborne dispersal of Stenocarpella maydis and S. macrospora conidia from naturally infected corn (Zea mays) straw. The data indicated that 93% and 88% of the total number of sampled conidia of S. maydis and S. macrospora, respectively, were trapped during the day, differing statistically from the night period. The number of sampled conidia of both fungi, was inversely proportional to the vertical and horizontal distance of spore traps from the inoculum source. Conidia were collected up to a height of 2.0 m and up to 120.0 m from the inoculum source. In both experiments, the frequency and the number of collected spores were the highest at a height of 25.0 cm and at a distance of 20.0 m from the inoculum source. Conidia was dispersed in the air as individual spores and/or grouped in cirri and not essentially associated to rain splashes.

Controle de doenças de plantas pela rotação de culturas

Esta revisao aborda a importância da escolha e da adocao de praticas culturais e seus reflexos na intensidade de doencas de plantas. Sao apresentados conceitos basicos referente ao tema e os de rotacao e monocultura. Discutem-se os principios ou fundamentos e potencialidade do uso da rotacao e do manejo integrado de doencas, as consequencias da nutricao de fitopatogenos, dos eventos biologicos ocorrentes nos restos culturais, as caracteristicas dos fitopatogenos potencialmente controlaveis e dos nao controlaveis pela rotacao.

Efeitos da rotação de cultura, de cultivares e da aplicação de fungicida sobre o rendimento de grãos e doenças foliares em soja

A rotacao de culturas e um metodo eficiente e de baixo custo para o controle de doencas de final de ciclo (DFC) da soja (Glycine max). Em experimentos de campo, nas safras 1998/99 e 2000/01, avaliaram-se os efeitos da rotacao de culturas de verao, com os sistemas soja e milho (Zea mays), de diferentes ciclos e cultivares de soja e da aplicacao de fungicidas, sobre a ocorrencia e intensidade das DFC. Na safra 98/99, detectou-se diferenca significativa no rendimento de graos na comparacao da media dos dois sistemas (soja/soja e soja/milho), devido, principalmente, ao controle da podridao-parda da haste, que causou danos em monocultura. Nao houve diferenca significativa para o uso de fungicida na parte aerea na safra 98/99 para o rendimento. Na safra 00/01 nao houve efeito significativo da rotacao para intensidade de oidio e DFC. A aplicacao de fungicidas proporcionou menor severidade do oidio e das DFC, diferindo significativamente da testemunha em todos as cultivares. Em relacao a severidade do oidio e das DFC houve diferencas significativas para a aplicacao de fungicida. A maior resposta em rendimento de graos foi obtida nas cultivares suscetiveis ao oidio. Os maiores rendimentos de graos foram detectados quando a soja foi cultivada em rotacao com o milho e com a aplicacao de fungicidas, principalmente nas cultivares suscetiveis ao oidio, e na safra 00/01 devido a maior precipitacao pluvial onde houve maior severidade de DFC.

Decomposição dos restos culturais do milho e sobrevivência saprofítica de Stenocarpella macrospora e S. maydis

Em amostras de colmos de milho (Zea mays) coletadas em lavouras comerciais, conduzidas no sistema plantio direto, localizadas na Regiao do Planalto Medio do Rio Grande do Sul, no periodo de 1998 a 2000, determinou-se a sobrevivencia saprofitica dos fungos Stenocarpella macrospora e S. maydis. Constatou-se que a presenca da palha de milho infetada na epoca de semeadura assegura a sobrevivencia destes fungos e garante a presenca do inoculo para a cultura do milho. Nas avaliacoes feitas no ano de 1995, a decomposicao da palha do milho, mantida na superficie do solo, foi de 78,5% aos 29 meses apos a exposicao no campo. Nas avaliacoes procedidas no ano de 1999, aonde foi comparado o efeito da posicao do residuo cultural no solo, estimou-se que a decomposicao de segmentos de colmos infetados por S. maydis e S. macrospora mantidos na superficie do solo foi mais lenta do que quando foram enterrados. Apesar da frequencia dos picnidios de S. maydis e S. macrospora ter diminuido ao longo do tempo, a sua presenca foi detectada ate 320 dias em colmos mantidos na superficie do solo. A viabilidade dos conidios de S. maydis e S. macrospora nos colmos mantidos na superficie do solo foi superior a 90%, apos 320 dias de exposicao dos colmos no campo. Os resultados demonstraram que no sistema plantio direto a presenca da palha de milho infetada assegura a sobrevivencia dos fungos S. maydis e S. macrospora.

Perfilhamento, área foliar e produtividade do milho sob diferentes arranjos espaciais

The objective of this work was to evaluate the effect of plant spatial arrangement on maize tillering, leaf area, and grain productivity. The experiments were carried out in the spring/summer of the 2007/2008 and 2008/2009 growing seasons. Treatments consisted of four plant densities (three, five, seven, and nine plants per square meter) and three row spacings (0.4, 0.7, and 1.0 m). The leaf area index (LAI) and grain yield of hybrid P30F53 were assessed, as well as the tiller contribution to these characters. In 2007/2008, there was no water deficit, LAI values were higher than 7, and tillers contributed with 65% of total LAI at the lowest plant density. In this year, grain yield average (13.7 Mg ha-1) was not affected by treatments, and tillers contributed with 44% of total yield at the density of three plants per square meter. In 2008/2009, there was water deficit before flowering and during grain filling, which decreased tillering and tiller contribution to LAI. Grain yield in this year increased from 9.7 to 11.7 Mg ha-1 with increasing plant densities, but tiller contribution to grain yield was lower. Tillering increases phenotypic stability of grain productivity to variations in plant spatial arrangement.

Modelo de ponto crítico para estimar danos de doenças foliares do trigo em patossistema múltiplo

A critical-point model to estimate damage caused by wheat leaf diseases in a multiple pathosystem Wheat leaf diseases cause damage by reducing photosynthetic activity in leaves. The objective was to obtain damage model equations for a wheat multiple pathosystem, by examining the relation between grain yield and the incidence of leaf diseases at different plant growth stages. The experiments were carried in Lages and Sao Jose do Cerrito, SC, during the 2005/06 and 2006/07 crop seasons with cultivars Onix and BRS Louro. The gradient of disease incidence was obtained by the number of fungicide applications (one, two, and three) and three different fungicide rates: azoxystrobin+cyproconazol (40+16, 60+24 and 80+32 g of a.i. ha -1

Viabilidade de Fusarium graminearum em sementes de trigo durante o armazenamento

A intensidade da giberela em espigas de trigo tem aumentado em funcao da adocao generalizada do plantio direto, com consequente aumento da incidencia do agente causal em sementes. Sementes de trigo da cultivar Fundacep 36, com 29,8% de incidencia natural de Fusarium graminearum, foram armazenadas em sacos de polipropileno trancado, em câmara climatizada, com temperatura entre 18 e 20oC e controle parcial de umidade relativa do ar, durante 12 meses. O objetivo foi quantificar a viabilidade do fungo em funcao do tempo de armazenamento. As analises foram procedidas a intervalo de dois meses, por um periodo de 14 meses. Em cada epoca de avaliacao Telles Neto, F.X.B.; Reis, E.M.; Casa, R.T. Viabilidade de Fusarium graminearum em sementes de trigo durante o armazenamento. Summa Phytopathologica, v.33, n.4, p.414-415, 2007. RESUMO

Época de aplicação e desempenho de fungicidas no controle da giberela em trigo

The chemical control of the wheat scab can be affected by time of application and fungicide. In the 2004 growing season, the fungicides were applied in the plant growth stage of beginning of flowering, half of complete flowering and beginning of soft dough stage. In the 2005 growing season, one only fungicides application was done in the beginning of the flowering with a larger number of fungicides. The applications were done with manual spray, with CO2 gas pressure in an outflow of 200L ha-1. The intensity of wheat scab was quantified by the incidence, severity and index of giberela. Grain yield, weight of a thousand grains and the incidence of Fusarium graminearum in the grains were also evaluated. The high porcentual of wheat scab control occurred when the application was done in the beginning of the flowering. The fungicides metconazol (0.09L i.a. ha-1), tebuconazol (0.15), trifloxystrobin+tebuconazol (0.075+0.15), azoxystrobin+ciproconazol (0.060+0.024) and pyraclostrobin+epoxiconazol (0.099+0.037) reduced significantly the intensity of giberela wheat, obtaining average control of 46% on incidence, 46.6% on severity and 71.2% on index of giberela wheat. These fungicides showed grain yield average of 23.4%, but a low efficiency on F. graminearum infection control in grains.