Investigation of crop calendar effect on spraying of autumn wheat fields in Varamin region

Spraying is one of the most important agricultural operations in protection stage. It should be prevented from immoderate application of these pesticides/herbicides, while weeds, pathogens and insects are controlled in this stage. Apparently, establishing an appropriate time for spraying operation, estimating the number of required and approved days for this operation as well as weather observations are quiet necessary to achieve this target. In this study, four limiting factors including rain, wind speed, temperature and relative humidity were considered for spraying operation and the approved ranges were determined accordingly. To data analysis, each month is divided into six Five-day sections. According to weather observations related to 24 years (1994–2018), the numbers of working days were determined within the appointed ranges, considering the limiting factors. T test is then employed to determine probable average ranges. Based on the results, among the limiting factors, temperature was the most effective factor to determine the number of working days for spraying operation. According to this, totally 11.9 days were appropriate for this operation in a crop season. In this regard, the total number of days for chemical control of thin-leaf and broad-leaf weeds, aphids, grasshoppers, bugs and Hadena basilinea were 17.9, 19.4, 21.2, 11.9 and 16.9 days in a crop season, respectively.