Farmers in Punjab and Haryana are burning stubble at night to evade detection by satellite and local officials working overtime to contain farm fires that have poisoned the air in Delhi NCR, it is learnt. According to official data, incidents of farm fires have reduced this year. Between September 15 and November 7 this year, nearly 21,000 farm fires have been reported in Punjab. This is a drop of about 30 per cent when compared to the same period last year.