Critical-point yield model to estimate yield damage caused by Cercospora zea-maydis in corn

Abstract

A model to estimate damage caused by gray leaf spot of corn (Cercospora zea-maydis) was developed from experimental field data gathered during the summer seasons of 2000/01 and during the second crop season [Januaryseedtime] of 2001, in the southwest of Goiás state. Three corn hybrids were grown over two seasons and on two sites, resulting in 12 experimental plots. A disease intensity gradient (lesions per leaf) was generated through application, three times over the season, of five different doses of the fungicide propiconazol. From tasseling onward, disease intensity on the ear leaf (El), and El -1, El -2, El + 1, and El + 2, was evaluated weekly. A manual harvest at the physiological ripening stage was followed by grain drying and cleaning. Finally, grain yield in kg.ha -1 was estimated. Regression analysis, performed between grain yield and all combinations of the number of lesions on each leaf type, generated thirty linear equations representing the damage function. To estimate losses caused by different disease intensities at different corn growth stages, these models should first be validated. Damage coefficients may be used in determining the economic damage threshold.Additional keywords: gray leaf spot, Zea mays, losses. RESUMO Modelo de ponto crítico para estimar os danos causados por Cercospora zea-maydis em milhoDesenvolveu-se um modelo para estimar os danos causados pela cercosporiose (Cercospora zea-maydis) na cultura do milho, com base em dados experimentais de campo, coletados nas safras de verão nos anos 2000/01 e na safrinha de 2001, no sudoeste goiano. Três cultivares de milho híbrido foram semeados em dois locais perfazendo um total de 12 experimentos. O gradiente da intensidade da doença, avaliada em função do número de lesões por folha, foi gerado pela aplicação de cinco doses em três épocas. A intensidade da doença foi avaliada, semanalmente, em cinco folhas, a partir do embonecamento: folha da espiga (Fe), Fe -1, Fe -2, Fe +1 e Fe +2. A colheita foi realizada na maturação fisiológica e o rendimento de grãos expresso em kg.ha -1 . As análises de regressão entre o rendimento de grãos e o número de lesões nas cinco folhas foram realizadas para todas as combinações obtidas e geraram 30 equações lineares da função de dano. Para estimativas de danos causados por diferente intensidade da doença, em diferentes estádios de desenvolvimento fenológico, esses modelos devem, antes de tudo, serem validados. Os valores dos coeficientes de dano podem potencialmente serem utilizados no cálculo do limiar de dano econômico.Palavras-chave adicionais: mancha foliar cinzenta, Zea mays, danos.

Guava fruit loss caused by rust

“…The single-point model has been employed to study the loss due to several diseases (23,24). Reis et al (24) have conducted trials to quantify the loss caused by Cercospora zea-maydis in corn and have reported that the single-point stage is feasible to predict the loss and calculate the economic loss threshold.…”

Critical yield-point model to estimate damage caused by brown spot and powdery mildew in barley

“…This result may be attributed to the more severe levels of powdery mildew in these plant GS, which was favored by the low rainfall during this period. Powdery mildew reduces the active foliar photosynthetic area by reducing of light absorption REIS et al (2008) wheat and oat data, respectively. The authors indicated that early disease onset in winter cereal in Southern Brazil has an impact on the grain yield, due to interference with the grain number per m 2 , which is determined by the tiller development (COOK et al, 1999).…”

“…Each plot had an experimental unit area of 5.0x2.5m. To generate the disease gradients, strobilurin and triazol fungicide rates (one half and full recommended rates) and numbers of fungicides sprays (once, twice, third and fourth) were applied, according to REIS et al, (2000REIS et al, ( , 2002REIS et al, ( , 2008, BOHATCHUK et al (2008) andNERBASS et al (2010). The fungicide applications were performed at the plant GS 22 (Main shoot and 2 tillers), GS 31 (Swelling 1st node detectable), GS 39 (Flag leaf ligule just visible), GS 45 (Full-boot, boot above ligule of 2nd last leaf) and GS 56 (50% of spikes visible), according to the diagrammatic scale of ZADOKS et al (1974).…”

Modelos Integral E De Ponto Crítico Para Estimar Danos No Rendimento E Seus Componentes Pela Mela Na Cultura Do Feijoeiro

“…Para a quantificação de danos existem vários métodos, entre eles os de ponto crítico, múltiplos pontos, modelo integral, superfície de resposta e sinecológico (Bergamin-Filho e Amorim, 1996). Existem vários trabalhos sobre os danos ocasionados por algumas doenças em outras culturas, encontrando em arroz (Marchetti e Bollich, 1991, Araújo et al, 2006, Pereira-Goulart et al, 2007, aveia (Reis et al, 2008;Nerbass et al, 2010), grão de bico (Navas-Cortés et al, 2000), trigo (King, 1976;Reis et al, 2000;Casa et al, 2004;Reis et al, 2006;Bohatchuk et al, 2008) e milho (Nutter e Jenco, 1992;Reis et al, 2007). Já em feijão, existem alguns trabalhos com os patógenos Phaeoisariopsis griseola (Bergamin-Filho et al, 1997;), Macrophomina phaseolina (Mayek-Pérez et al, 2003), Xanthomonas campestris pv.…”