Effect of nitrogen fertilizer and planting dates on stem borer and blast disease and yield in replanted rice cultivars in Amol, Iran

To determine the effects of planting date and nitrogen fertilizer on stem borer, blast disease and rice yield of in replanted rice cultivars of Koohsar, Binam, Tarom Hashemi, and Tarom Mahali, two separate experiments were carried out in split plot based on randomized complete block design during the growing years of 2015-2016 in Amol, Iran. The first experiment was the effect of nitrogen fertilizer with the amounts of 30, 60, and 90 kg/ha on rice cultivars. The second one was the effect of planting dates including 24 July, 3, 11, and 13 August on severity of stem borer, blast disease and rice cultivars yield. The severity of stem borer was about 18 on Koohsar, and 6 ~ 12% on Binam, Tarom Hashemi, and Tarom Mahali cultivars. The increase of nitrogen application rate resulted in significant increase of stem borer severity in vegetative and reproductive stages.The amounts of panicle node blast in Koohsar and Binam cultivars were 21 ~ 43 and 4%, respectively. Increasing nitrogen rate caused significantly higher rice yield, but application of 90 kg/ha N increased the severity of stem borer. There was no significant difference in stem borer severity among the studied cultivars. The stem borer and blast disease severity was in maximum level in the first planting date. Panicle node blast severity in Koohsar was more than local rice cultivars in all three planting dates. To obtain higher rice yield and less damage of stem borer and blast disease in rice replanting system, the second  planting date and 60 kg/ha of N fertilizer is recommended.