INTRODUCTION
The fungal seed born disease popularly known as Karnal bunt is generally expressed as a cool winter/spring weather disease in the North. The weather conditions during the susceptible period are critical factors in bunt development. An average temperature range of 18 °C to 22 °C, coupled with high relative humidity (morning) or the day relative humidity, is considered optimum for infection. In the study of various diseases, it appearance in or over the crops, plants, trees and its economical product parts or grains of the crops i.e. wheat, field crops and other which were influenced by the weather condition along with the crucial parameters. The weather fluctuation and variability and environment condition will be play the very crucial role to create the optimum favourable condition and resulted to cause the infestation. Long term weather parameters were analyzed i.e. temperature, relative humidity, radiation and rainfall from 1st to 12th standard meteorological weeks but 6th to 12 SMWs are favored to development of the grain infestation disease. Workneh et al. (2007) studied the weather variables (temperature and rainfall amount and frequency) were collected and used as predictors in discriminant analysis for classifying bunt positive and -negative fields using incidence data for 1997 and 2000 to 2003 in San Saba County. Due to western disturbance in the North West part of the country were received the periodically rainfall to maintained the high level of relative humidity (Singh et al ., 2018). The higher level of relative humidity that can be maintained the higher humidity within the crop canopy and favored the fungal growth might be due to the increasing leaf or canopy wetting period. The momentum within the crop canopy will be reduced so higher level of humidity will be maintained. The simple linear regression model showed that the maximum temperature and morning relative humidity had maximum influence on the development of leafhopper population. The stepwise linear regression model was explained the coefficient of determination (R²) of leafhopper population with the range 40 to 90 per cent in respective year (Janu et al.,2018). sStansbury and McKirdy (2002) reported that there was a strong correlation (r :0.83) between the Humid Thermal Index (HTI) model, which used long-term, average-monthly data, and the rainfall model, which was based on the per cent chance of at least three Suitable Rain Events (SRE) during the susceptible period (August to October). Results suggest that northern wheat growing areas are too hot and dry (HTI<2.2, chance of SRE 15–27%), southern areas are marginal to too cold and/or wet (HTI > 3, chance of SRE 68–97%), eastern areas are marginal to too hot and dry (HTI around 2.2, chance of SRE 24–50%), and western areas are suitable (HTI between 2.2 and 3.3, chance of SRE 41–78%).