NITROGEN RATES AND SOWING DATES INFLUENCE THE SEVERITY OF WHITE SPOT DISEASE AND GRAIN YIELD OF MAIZE

The objective of this study was to analyze the effects of nitrogen rates and sowing dates on the severity of white spot disease (WSD) in first season maize hybrids, and their correlation with relative chlorophyll content, thousand grain weight and yield. The experiment was set in a randomized block design with treatments arranged in split-split plots. Two hybrids were tested in the main plots: AG9025 PRO3 (super early) and 30F53 VYH (early). Two sowing dates were evaluated in the split plots: preferential (9/20/2016) and late (12/05/2016). Four nitrogen rates were applied in the split-split plots. Nitrogen rates were top-dressed at the V4, V8 and V12 vegetative stages. The relative chlorophyll content reading was performed at VT stage. The quantification of WSD severity was made at R6, using diagrammatic scale. The AG9025 PRO3 hybrid showed higher average WSD severity (17.7%) than the 30F53 VYH (9.3%). The preferential sowing date showed lower severity (2.2%) compared to the late sowing date (31.4%). There was a significant positive correlation between the disease severity and the relative chlorophyll content, thousand grain weight and grain yield, except for the 30F53 VYH hybrid on the late sowing date. The hybrid AG9025 PRO3 showed increase in WSD severity when the highest nitrogen rates were applied, on both sowing dates. The effect of N rates on WSD was not significant for the 30F53 VYH hybrid. The late sowing time generates greater disease severity. The AG9025 PRO3 hybrid is more susceptible and the severity of its white spot is increased with the increment in N doses. There is a positive correlation between the relative chlorophyll content, disease severity, yield and thousand grain weight.