Assessment of the Effects of Fertilizer Applications on Gray Leaf Spot and Yield in Maize

Abstract

The effects of the application of 0, 60, and 120 kg N ha-1 and of 0, 25, 50, and 150 kg K ha-1 on final disease severity, standardized area under disease progress curve, and grain yield were investigated at Cedara, South Africa, on a maize (Zea mays) hybrid susceptible to gray leaf spot (GLS), caused by Cercospora zeae-maydis. The trial was a randomized 3 × 4 factor design, split for fungicide treatments, and replicated three times. With increased N and K levels, final percent leaf blighting and the standardized area under disease progress curve were higher. In fungicide-treated maize, grain yields increased with increasing levels of N and K, as expected. In non-fungicide-treated maize, grain yield increased significantly with increased levels of N, despite increased disease severity. This was in contrast to small increases in grain yields from non-fungicide-treated maize with increased K levels, which were not significant. This was probably because grain yield response, which should have occurred at higher K applications, was reduced by increased disease severity. The effect of N, P, and K on GLS wasinvestigated at Ahrens. Maize was grown in a 4 × 4 × 4 N-P-K factorial, in a randomized complete block design. Fertilizer was applied at 0, 60, 120, and 180 kg N ha-1, 0, 30, 60, and 120 kg P ha-1, and 0, 50, 100, and 150 kg K ha-1. No fungicides were applied. A single disease assessment at physiological maturity showed that final disease severity increased with increasing levels of N, P, and K. These results have implications for small-scale farmers who are encouraged to fertilize for increased grain yields but may not have the resources to apply fungicide sprays to control fungal diseases.

Influence of Nitrogen Content on Rice Leaf Sheaths on Sheath Blight Development

“…The excess of N may inhibit the production of host defense compounds in response to pathogens infection (HUBER 1980). Caldwell et al (2002) studying the effect of the different rates of N applied in maize observed increase of gray leaf spot for the biggest N rate. Tomato plants that received N application were more susceptible to Oidium lycopersicum (HOFFLAND; JEGER; BEUSICHEM, 2000).…”

REAÇÃO DE HÍBRIDOS DE MILHO À Curvularia ssp, SOB DOIS NÍVEIS DE ADUBAÇÃO COM NITROGÊNIO, NO SUL DO TOCANTINS

“…Esses valores confirmam que, embora exista variabilidade genética quanto à resistência a mancha de Curvularia em ambos os níveis de adubação de cobertura, em condições de alto nível de nitrogênio, a variância genética é superior a observada em baixo N. Com isso, o sucesso de seleção de cultivares resistentes a mancha de Curvularia é mais favorável em alto N. De acordo com Cruz (2006) quanto maior o valor de variância genética maior o sucesso de seleção. Esse maior valor de variância genética em alto N, principalmente na segunda avaliação da mancha de Curvularia pode ser devido a altas doses de nitrogênio favorecer a infecção e o desenvolvimento de doenças fúngicas (Caldwell et al, 2002). Isso pode ter ocorrido devido à alta concentração de nitrogênio nas plantas reduzir a produção de compostos fenólicos (fungistáticos) e de lignina nas folhas, diminuindo a resistência aos patógenos (Marschner, 1986).…”

Nitrogen and potassium fertilization on the yield and intensity of the maize white spot

“…The lowest severity levels were observed at the lowest dose of N, combined to the highest dose of K, and nitrogen fertilization influenced the K content negatively in the upper canopy. Caldwell et al (2002) also report an increase in the severity of cercosporiosis (Cercospora zeae maydis Tehon & Daniels) of corn with increased doses of N (0, 60 and 120 Kg ha -1 ) and K (0, 25, 50 and 150 Kg ha -1 ) in the soil. However, there is still no information about the influence of N and K have upon the maize white spot.…”