Epidemiological Studies on Leaf Blights of Maize Caused by Exerohilum turcicum (Pass.) Leonard and Suggs and Bipolaris maydis (Nisik. and Miyake)

The Field experiments conducted at Maize Research Station,Vagarai, Tamil Nadu, India during kharif 2019, 2020 & 2021 to study the disease development in relation to weather parameters, viz., temperature, relative humidity, rainfall with the leaf blights of maize. Observations on the spore load and disease grade were taken from 33rd standard week to 44th standard weeks at weekly interval. Increased spore load of 13 to 48 Nos. / Microscopic observations for TLB and 3 to 5 Nos./microscopic observations with the temperature ranges between 22-35◦C, Humidity 48-72% and 19-24° Dew will lead to the TLB & MLB disease incidence with the grade of 1to 4 was observed. Based on the observations, the first appearance of leaf blight diseases were observed between 35th and 45th days after sowing with the grade of 1 (34th meteorological standard week). The disease grade increased from 1 to 4 as the age of the crop increases. There was a sudden increase in disease intensity because of increased scattered showers and increased relative Humidity (44th meteorological standard week). Temperature has not much influenced the disease development, since it was almost uniform throughout the cropping season in these three years. From the dataset, we would like to highlight that 34th and 44th meteorological standard weeks are highly critical for leaf blight disease development. Hence, spraying with mancozeb or zineb @ 2-4 g/l or propiconazole 25% EC @ 1ml/l during 34th and 44th meteorological standard week is recommended to manage the disease during kharif seasons in Tamil Nadu.